Evaluation of abdominal radiographs begins and ends with a systematic approach. We evaluate the quality of the radiographs first and then proceed with an orderly examination of the anatomy (Tables 2.7 and 2.9). When evaluating anatomy, most of us look at a structure’s position first, followed by its size, shape, and opacity. We initially look for each organ or body part in an expected location. All of the abdominal viscera are soft tissue opacity. The individual organs are distinguished because peritoneal and omental fat provide the opacity interfaces needed to visualize their serosal margins (Figure 4.1). When intra‐abdominal fat is absent or obscured by fluid, serosal margins are less distinct or may not be visible at all. In emaciated animals, there often is insufficient fat to provide an opacity interface. Fluid in the abdominal cavity may result from inflammation or effusion. Because fluid is the same opacity as the soft tissue structures, the serosal margins become less distinct. Visceral crowding also can obscure serosal margins because fat may not visible between the borders of the contiguous soft tissue structures. Figure 4.1 Opacity interfaces. Lateral view of a dog abdomen depicting serosal and mucosal margins. The serosal margins (black arrows) are visible because of adjacent fat. The mucosal margins (white arrows) are visible because of adjacent gas. An opacity interface also is needed to see mucosal margins. Unless the mucosa is outlined by gas or a positive contrast medium it cannot be accurately evaluated. This is because any adjacent fluid or soft tissue material will blend with the mucosa. The thickness of visceral walls seldom can be reliably assessed with survey radiographs. In addition to radiography, other non‐invasive imaging modalities are available to examine the abdominal viscera. Ultrasonography, computed tomography, magnetic resonance imaging, and nuclear medicine imaging are increasingly utilized in veterinary medicine and may provide diagnostic information not available from radiography. This book is specific to radiography, but keep in mind that these other diagnostic tools may be available. At the end of this chapter are extensive lists of differential diagnoses for the numerous radiographic findings being discussed. Patients should be encouraged to urinate and defecate prior to radiography. An empty colon and a small urinary bladder can lessen visceral crowding and reduce summation artifacts. For elective radiographs, the GI tract should be empty. Many abdominal radiographs are rendered non‐diagnostic due to the presence of ingesta. A 12‐hour fast allows the stomach to empty and an 18‐ to 24‐hour fast allows the intestines to empty. Patients should have free access to water during fasting. When practical, drugs that affect GI motility should be discontinued 24–48 hours prior to abdominal radiography, including sedatives and anesthetic agents that slow GI peristalsis (e.g., xylazine). Cleansing enemas may be needed to empty the large intestine. Either a mixture of water and mild soap or a saline solution are acceptable enemas and should be administered 2–4 hours prior to radiography. Enema solutions that are below body temperature may help stimulate the expulsion of gas from the colon. Enemas are contraindicated in patients with acute abdominal pain, active vomiting, or a palpable abnormality in the abdomen. Enemas are not recommended prior to initial radiographs in patients being evaluated for GI disease. This is because an enema can alter the pattern of gas and fluid in the intestinal tract, which may mask or mimic pathology. Phosphate enemas are not recommended because they can be toxic, especially in cats and small dogs. Clean and dry the patient’s hair coat and skin as needed prior to radiography. Move any monitoring equipment, such as ECG leads, out of the field‐of‐view (FOV). Note any cutaneous or subcutaneous growths that may create superimposition artifacts. For accurate technical settings, measure the thickness of the abdomen at its widest part, which typically is over the liver at the level of the xyphoid or 12th rib. Center the x‐ray beam in the middle of the abdomen, midway between the diaphragm and the pelvic inlet. This helps minimize distortion at either end of the abdomen. Landmarks for centering include the level of the umbilicus or just caudal to the last rib. Collimate the FOV to include the entire abdomen from the diaphragm to the pelvic inlet. The landmark for the diaphragm is about the T8 thoracic vertebra and the landmark for the pelvic inlet is the greater trochanters of the femurs. Collimation should include the spine dorsally and the body walls laterally and ventrally (Figures 4.2 and 4.3) Figure 4.2 Normal canine abdomen. Lateral view (A) and VD view (B) of a dog abdomen depicting radiographs that are properly positioned, centered, collimated, and exposed. L = liver, S = stomach, RK = right kidney, LK = left kidney, Sp = spleen, SI = small intestine, C = colon, B = urinary bladder. Figure 4.3 Normal feline abdomen. Lateral view (A) and VD view (B) of a cat depicting a normal abdomen. L = liver, F = falciform fat, S = stomach, RK = right kidney, LK = left kidney, Sp = spleen, SI = small intestine, C = colon, B = urinary bladder. The yellow arrows point to the borders of the hypaxial muscles, which tend to be relatively larger and more visible in cats than in dogs. The pelvic limbs should be moved caudally to eliminate superimposition. Avoid overstretching the patient as this will distort the shape of the abdomen and increase visceral crowding, especially in cats and small dogs. Align the spine and sternum in the same anatomical plane. Use body markers to indicate Right or Left and whether horizontal beam radiography was performed. Make the exposure at the end of expiration to minimize motion artifact as most patients pause breathing momentarily at the end of expiration. Expiration also allows the diaphragm to move cranially, which expands the abdominal cavity and lessens visceral crowding. Orthogonal radiographs are needed for complete evaluation of the abdomen. Standard radiographs for most abdominal studies include either a right or left lateral view (Figure 2.16) and a VD view (Figure 2.17). The DV view is not routinely made because serosal margins are less distinct due to visceral crowding. The right lateral view is useful to move stomach gas into the fundus and to move stomach fluid into the pylorus (Figure 4.4). The radiographic appearance of fluid and gas in the stomach depends on the volume of each. In a right lateral view, the kidneys tend to be further separated than in a left lateral view and the margins of the liver and spleen may be easier to identify. The left lateral view allows stomach gas to rise into the pylorus and stomach fluid to flow into the fundus. This is helpful when differentiating a fluid‐filled pylorus from a cranioventral abdominal mass. Figure 4.4 Right lateral vs. left lateral. Right lateral view (A) and left lateral view (B) of a dog abdomen depicting the differences between the two views. In right lateral recumbency, fluid in the stomach flows into the pylorus (white arrow) and gas rises to the fundus (black arrow). In left lateral recumbency, fluid flows into the fundus and gas rises to the pylorus and duodenum (white arrows). The margins of the liver (L) and spleen (Sp) sometimes are better visualized in a right lateral view than in a left lateral. The right and left kidneys (RK and LK) tend to be further separated in a right lateral view. The VD view is useful to move stomach gas into the body of the stomach and to move stomach fluid into the fundus and pylorus (Figure 4.5). The DV view allows stomach gas to rise into the fundus and pylorus and stomach fluid to flow into the body of the stomach. It usually is easier to position a patient straight for a VD view than a DV view (Figure 2.18), however, some patients will not tolerate being in dorsal recumbency. When neither a VD nor DV view is possible, make both the right lateral and the left lateral views. Making both right and left lateral views can alter the positions of the moveable viscera and change the distribution of fluid and gas in the hollow organs, which may reveal lesions that were not initially evident. Figure 4.5 VD vs. DV. VD view (A) and DV view (B) of the same dog abdomen depicting some of the differences between the two views. In dorsal recumbency, there are three humps to the diaphragm and gastric gas rises into the body of the stomach (yellow arrow). In ventral recumbency, there is one hump to the diaphragm and gastric gas rises to the fundus (black arrow) and pylorus (white arrow). The serosal margins are less distinct in a DV view than a VD due to visceral crowding. Supplemental views sometimes are needed to confirm or further evaluate a suspected lesion. For example, when the stomach or colon is not recognized in initial radiographs, gas may be added to help identify them. To add gas to the stomach, a small volume of carbonated beverage may be given per os or air administered through a gastric tube. To identify the colon, a small volume of room air can be infused per rectum. Flexed VD view (“frog‐legged view”) flexing the pelvic limbs with the patient in dorsal recumbency may be preferred to an extended VD view to eliminate superimposition of the inguinal skin folds and to lessen visceral crowding (Figure 4.6). Figure 4.6 Inguinal skin folds. An extended VD view (A) and a flexed VD view (B) of the same dog abdomen depicting the appearance of skin folds and visceral crowding. With the pelvic limbs extended, the inguinal skin is stretched to create superimposition artifacts (white arrows). Extension also narrows the abdomen, which can crowd the organs and make serosal margins less distinct. The flexion or “frog‐leg” view allows the abdomen to expand and may improve the visualization of serosal margins. Oblique views are used to eliminate superimposition of overlying structures. For example, rotating the patient 10° or 20° from a true VD or lateral view may reduce summation of the spine or intestines on an area of interest (Figure 2.12). The oblique view can be further modified by collimating the field of view to a specific area and centering the x‐ray beam on that area to make a tangential view. Tangential views are used to better visualize a peripheral lesion, such as a mass in an abdominal wall. The patient is rotated or the x‐ray tube is angled so the x‐ray beam strikes the lesion in profile rather than en face (Figure 2.13). The FOV should be collimated to the size of the lesion to lessen scatter radiation and sharpen radiographic detail. Horizontal beam radiography takes advantage of gravity to reposition fluid, gas, and viscera. It may be used to detect small volumes of free fluid or gas in the abdominal cavity or to better visualize an intra‐abdominal mass that was obscured by viscera or fluid in the initial radiographs. Fluid flows to the dependent (down) part of the abdomen and gas rises to the uppermost part. The patient may be standing, held vertically, or positioned in lateral, dorsal or ventral recumbency, depending on the purpose of the view (Figure 2.15). The image receptor is placed alongside the patient, and the x‐ray beam is directed across the table (horizontally) to make a VD or lateral view. The source‐to‐image distance should be the same as for vertical radiography (typically 100 cm or 40 inches) and you should follow the same guidelines for centering the x‐ray beam and collimation. Abdominal compression is a useful technique to displace overlying viscera away from an area of interest (Figure 2.19). For example, the abdomen may be gently compressed using a low opacity paddle (e.g., a plastic or wooden spoon) to push the intestines away from the urinary bladder, the uterus, a kidney, or a mass. The x‐ray exposure is decreased to compensate for the reduced abdominal thickness; typically, the exposure time is reduced by half. Compression radiography is contraindicated in patients with a tense or painful abdomen, peritoneal effusion, or a mass that is at risk for rupture. The urethral view is used to better visualize the urethra in male dogs by moving the pelvic limbs cranially while the patient is in lateral recumbency (Figure 2.20). The patient’s age, body type, body condition, and position at the time of radiography can affect the appearance of the abdominal structures. Some of the more frequently encountered factors are described below. Figure 4.7 Immature abdomen. Lateral view of a 2‐month‐old puppy abdomen depicting indistinct serosal margins. Immature fat is more opaque than adult, which weakens the opacity interface with soft tissues. The patient’s young age is evident from the open growth plates in the vertebrae and pelvis (yellow arrows), the relatively large size of the liver, and the incomplete mineralization of the costal arch. The borders of the abdominal cavity include the diaphragm cranially, the sublumbar muscles dorsally, the pelvic inlet caudally, and muscular walls laterally and ventrally. The sublumbar muscles are also called hypaxial muscles or psoas muscles. Parietal peritoneum lines the diaphragm and muscular walls. Visceral peritoneum covers most of the abdominal organs and forms the mesentery. Between the parietal and visceral peritoneum is the peritoneal space (Figure 4.8). Figure 4.8 Peritoneum. This illustration depicts a cross‐sectional view of the abdomen. The peritoneal space is enlarged and colored yellow for demonstration purposes. It normally contains only a small amount of fluid for lubrication. Parietal peritoneum is shown in red and visceral peritoneum in blue. The kidneys are located in the retroperitoneal space (colored green). Only the ventral borders of the kidneys are covered by peritoneum. Folds of peritoneum form the falciform and gastrosplenic ligaments and the root of the mesentery. SI = small intestine, Du = duodenum, CVC = caudal vena cava, Ao = aorta, Ad = adrenal gland. The peritoneal space is considered a “potential space” because it contains only a small volume of fluid. It is not visible in radiographs. The peritoneal space surrounds the abdominal organs that are covered by the visceral perito neum. The organs that usually are visible in survey radiographs include the liver, spleen, stomach, intestines, and urinary bladder. Peritoneal structures not generally seen include the gall bladder, pancreas, ovaries, uterus, lymph nodes, and blood vessels. The kidneys are located in the retroperitoneal space. The retroperitoneal space is the area dorsal to the peritoneal space and ventral to the sublumbar muscles. It extends from the diaphragm to the pelvis. The retroperitoneal space communicates cranially with the mediastinum (via the aortic hiatus) and caudally with the pelvic canal. In addition to the kidneys, structures in the retroperitoneal space include the adrenal glands, ureters, aorta, caudal vena cava, cisterna chyli, and lymph nodes. The kidneys usually are visible in survey radiographs and the aorta sometimes is identified. The other retroperitoneal structures rarely are distinguished unless enlarged or mineralized. A notable exception are the paired deep circumflex iliac arteries which branch from the caudal aorta at nearly a 90° angle. In a lateral view, one or both of these vessels often is seen end‐on to appear as a focal mineral opacity structure ventral to the caudal lumbar spine, sometimes mistaken for a ureteral calculus (Figure 4.9). This finding is similar to seeing an end‐on pulmonary vessel and mistaking it for a mineralized lung nodule (Figures 3.145 and 3.146). Rarely will more than one of these vessels be visible in radiographs. Figure 4.9 Deep circumflex iliac artery. Lateral view of a dog abdomen depicting end‐on visualization of a deep circumflex iliac artery (arrow), which may be mistaken for a ureteral calculus. There is no direct communication between the peritoneal space and the retroperitoneal space. Disease in one compartment rarely involves the other. Fat, however, is stored in both compartments. Fat deposits tend to be largest in the falciform ligament, omentum, mesentery, and caudal retroperitoneal space. The radiographic appearance of peritoneal and retroperitoneal fat normally is similar in opacity and homogeneity. Large fat deposits may be mistaken for a mass or fluid, particularly in overweight cats (Figure 4.10). However, most masses and all biological fluids are soft tissue opacity and should not be mistaken for fat. Figure 4.10 Falciform fat. Lateral view of a cat abdomen depicting a large amount of fat in the falciform ligament (arrow). Falciform fat may be mistaken for a mass or peritoneal effusion, but this is fat opacity, not soft tissue, and the falciform is a common site for fat deposition. Normal intra‐abdominal lymph nodes are not visible in survey radiographs. The visceral nodes are located in the peritoneal space and the parietal nodes are in the retroperitoneal space. The visceral nodes receive lymphatics from the cranial abdomen and drain into the cisterna chyli. The parietal or sublumbar nodes receive lymphatics from the spine, adrenal glands, kidneys, pelvic canal, and pelvic limbs and also drain into the cisterna chyli. The cranial mesenteric nodes are the largest visceral lymph nodes. They are located near the root of the mesentery. The medial iliac nodes are the largest sublumbar nodes and they are located ventral to the L5–7 vertebrae. There is considerable variation in the number and location of the sublumbar lymph nodes among dogs and cats. Sometimes these nodes are absent. A small or contracted abdomen may be due to loss of body fat or displacement of the abdominal viscera, the latter resulting from a hernia or rupture of the diaphragm or body wall. In emaciated patients, the abdomen may appear “tucked up” with a concave ventral border (Figure 4.11). The serosal margins often are indistinct because there is insufficient intra‐abdominal fat to create a visible opacity interface. Both the peritoneal and retroperitoneal spaces tend to be small. Figure 4.11 Emaciation. Lateral view of a dog abdomen depicting little intra‐abdominal fat. The ventral abdomen is concave and tucked‐up. The serosal margins are indistinct because there is insufficient fat for an opacity interface. Notice the lack of subcutaneous fat. Abdominal distention may involve the peritoneal space, the retroperitoneal space, or both. Disease in one space usually does not involve the other, which means the other space generally appears normal in radiographs. Conditions that can enlarge both spaces include excess fat in overweight animals and hemorrhage, the latter when caused by coagulopathy or severe trauma. Leakage of urine can also enlarge one or both spaces. An abdomen may appear distended due to weakening of the supporting ligaments and muscles. Weakening may be associated with old age or Cushing’s Syndrome (hypercortisolism). The abdomen may appear to sag or to be pendulous, but serosal margins remain distinct, unless there is concurrent intra‐abdominal fluid or inflammation. Thickening (widening) of a body wall may be localized or diffuse. A thickened wall may or may not be accompanied by altered opacity. Localized thickening typically is due to a mass. A thickened abdominal wall that contains gas opacity may result from a penetrating wound, herniation of a gas‐filled structure, or migration of emphysema. Penetrating wounds (e.g., bite wounds, injections, surgery) generally produce a multifocal gas pattern, whereas a herniated bowel segment tends to be localized and confined. Migration of emphysema typically originates in the thorax (e.g., pneumomediastinum) and can become quite diffuse (Figure 3.63). Fat opacity in a diffusely thickened abdominal wall may be due to obesity or a dissecting lipoma. Obesity is bilateral, whereas lipomas tend to be unilateral. Localized fat opacity may represent an isolated lipoma or a hernia containing omental or falciform fat. Fat in the body wall may displace and outline muscle layers, providing an opacity interface with the soft tissue opacity of the muscles. A thickened abdominal wall that is soft tissue opacity may be due to subcutaneous fluid, a mass, or displaced viscera. Soft tissue opacity swelling may obscure fascial planes and muscle layers. Mineral or metal opacity in the abdominal wall usually is readily identified and may represent dystrophic mineralization or a foreign object. Superimposition artifacts can mimic abnormal opacity. A hernia is a protrusion through a natural opening; the peritoneum remains intact. A rupture is an acquired loss of body wall integrity; the peritoneum is damaged. The two rarely are distinguished in radiographs. The term hernia, therefore, commonly is used as a catch‐all phrase to describe the displacement of abdominal viscera outside the abdominal cavity. Displaced viscera create variable degrees of extra‐abdominal swelling. Swelling caused by a hernia may be difficult to distinguish from swelling caused by a tumor, cyst, or other mass. The opacity of the swollen area may provide clues to its contents. Fatty tissues tend to enter a hernia first (e.g., omentum, mesentery, falciform ligament). The most commonly displaced soft tissue structures are the intestines, stomach, liver, spleen, urinary bladder, and uterus. The identity of a displaced organ may be determined by recognizing its shape or its pattern or by noticing that it is absent from its normal location. GI structures often can be identified by their intraluminal gas. Displaced intestines commonly create curvilinear gas opacity tubes that extend beyond the limits of the abdominal cavity. A strangulated or incarcerated GI structure can dilate greatly to produce a very large cyst‐like mass (Figure 3.48). The abdominal cavity may appear “empty” when a significant amount of viscera is displaced. The serosal margins of the remaining organs usually are well‐visualized unless surrounded by fluid or there is insufficient body fat. Abdominal hernias vary in etiology and location (Figure 4.12). Diaphragmatic hernias, including traumatic, hiatal, and peritoneopericardial, are discussed in Chapter 3: Thorax. An umbilical, inguinal, or scrotal hernia may be congenital or acquired and may appear as either a soft tissue, fat, gas, or mixed opacity swelling in its respective area. Perineal hernias result from a weakened or ruptured pelvic floor and most often occur in older, intact males. They typically produce a swelling under the tail and may displace the rectum. Contents in a perineal hernia may include fluid, fat, urinary bladder, prostate gland, uterus, or/and intestine. Intra‐abdominal hernias occur when an organ protrudes through a tear in the mesentery. These may be visible in radiographs as a static bowel segment or dilated bowel if the segment becomes incarcerated (i.e., mesenteric hernia). Figure 4.12 Abdominal hernias. Lateral view of a dog abdomen depicting common sites of abdominal hernias: (1) diaphragm hiatus; (2) dorsal diaphragm; (3) ventral diaphragm; (4) umbilicus; (5) inguinal region; (6) perineal region. Abdominal radiographs that are less opaque than expected may be due to poor radiographic technique, excess intra‐abdominal fat, or free gas in the peritoneal or retroperitoneal space (see differential diagnoses). Excess fat is due to obesity or a large intra‐abdominal lipoma (Figure 4.13). Free gas may result from a penetrating wound, ruptured GI structure, recent laparotomy, or infection with gas‐producing bacteria. Figure 4.13 Intra‐abdominal lipoma. Lateral view (A) and VD view (B) of a dog abdomen depicting a large lipoma in the caudal abdomen. The lipoma displaces the small intestine cranially, the colon dorsally (arrows), and the urinary bladder (B) caudally. The soft tissue opacity left kidney (LK) is visible through the fat opacity lipoma. Abdominal structures or areas that appear more opaque than expected in radiographs may be due to poor radiographic technique, increased intra‐abdominal fluid, or visceral crowding (see differential diagnoses). Increased fluid and visceral crowding both lead to less distinct serosal margins. Fluid may result from inflammation or effusion. The type of fluid cannot be determined from radiographs because all biological fluids are soft tissue opacity. Gas is common in the GI tracts of dogs and cats. The volume of gas can vary greatly between patients and may or may not be clinically significant. Abnormal GI gas usually is accompanied by dilation or a persistently abnormal pattern. Gas within the wall or parenchyma of an organ (pneumatosis) is abnormal. Pneumatosis has been reported in the stomach, intestines, spleen, liver, uterus, gall bladder, and urinary bladder. It most often is caused by a gas‐producing bacterial infection (e.g., E. coli, pseudomonas), particularly in animals with diabetes mellitus. Pneumatosis also can result from damage to the mucosa and leakage of gas into the wall of the organ. Pneumoperitoneum is free gas in the peritoneal space. The etiology of pneumoperitoneum may not be evident from radiographs alone. Patient history and results of physical examination often provide valuable diagnostic information. Penetrating wounds frequently are accompanied by subcutaneous emphysema. Note: superimposition of subcutaneous gas can mask or mimic a pneumoperitoneum. Post‐operative gas generally is resorbed within a week, but gas can persist in the peritoneal space for as long as three to four weeks. In patients with pneumoperitoneum caused by a ruptured stomach or bowel segment, the damaged organ may be abnormally distended. Small volumes of peritoneal gas appear as irregular‐shaped bubbles or pockets of gas. Bubbles usually are unevenly distributed and frequently become trapped among the segments of small intestine. They appear as sharply‐marginated pockets of gas that are more linear or triangular in shape than the normal rounded, flowing intestinal gas pattern (Figure 4.14). Figure 4.14 Pneumoperitoneum. Left lateral view of a dog abdomen depicting free gas in the peritoneal cavity. Pockets of gas accumulate between the diaphragm and liver (black arrows) and form triangular‐shaped bubbles among the segments of small intestine (white arrows). Peritoneal gas rises to the highest part of the abdomen. Larger volumes of gas tend to collect between the diaphragm and the liver (Figure 4.14). Gas adjacent to the diaphragm, liver and stomach enhance their visualization due to the gas:soft tissue opacity interface. As gas continues to fill the peritoneal space, more and more serosal margins may become more distinct. However, pneumoperitoneum often is accompanied by peritoneal inflammation or effusion, which may obscure serosal margins. A large volume of free gas in the peritoneal cavity can cause an overall decrease in abdominal opacity which may be mistaken for an overexposed radiograph. Examine the extra‐abdominal structures to determine whether the exposure was correct. Peritoneal gas tends to be freely moveable. Its distribution is affected by gravity and the position of the patient at the time of radiography. Small volumes of free gas may be easier to detect with horizontal beam views (Figure 2.15). In lateral recumbency, gas rises to the uppermost part of the peritoneal space and tends to collect under the ribs (Figure 4.15). Left lateral recumbency is preferred over right lateral recumbency because the gas that normally is present in the gastric fundus and colon may be mistaken for peritoneal gas. In dorsal recumbency, free gas is likely to collect between the ventral body wall and the liver (Figure 4.16). Keep in mind that it takes some time for peritoneal gas to redistribute, so allow the patient to remain recumbent for about 5–10 minutes prior to making the radiograph. For patients in distress, a standing lateral view may be preferred, in which case free gas rises dorsally to collect in the sublumbar region. Figure 4.15 Horizontal beam view. VD view of a dog abdomen made with the patient in left lateral recumbency and the x‐ray beam directed horizontally (across the table). Free gas rises to the uppermost part of the peritoneal space and is depicted under the ribs (white arrow). A normal gas:fluid line is depicted in the gastric pylorus (black arrow). Figure 4.16 Horizontal beam radiography. Lateral view of a dog abdomen made with the patient in dorsal recumbency and the x‐ray beam directed horizontally (across the table). Free gas rises to the uppermost part of the peritoneal space and is depicted between the ventral body wall and the liver (white arrow). A normal gas:fluid line is depicted in the stomach (black arrow). Pneumoretroperitoneum is free gas in the retroperitoneal space. The margins of the kidneys, aorta, and sublumbar muscles often become more visible due to the gas outlining their margins (Figure 3.63). Causes of a pneumoretroperitoneum include a penetrating wound, migration of gas from a pneumomediastinum, and infection with gas‐producing bacteria. An increase in intra‐abdominal fluid may result from inflammation or effusion. The type of fluid cannot be determined from radiographs. Peritoneal inflammation (peritonitis) creates more fluid due to increased blood flow and capillary leakage. The inflammation may be localized or diffuse. Serosal margins in the inflamed area appear hazy and indistinct due to fluid effacement. Peritonitis can progress to effusion and complete loss of visualization of serosal margins. Effusion may or may not cause abdominal distention. The retroperitoneal space is normal as long as the inflammation is confined to the peritoneal space. Peritonitis can alter peristalsis in the nearby intestines and cause stasis in one or more bowel segments. A static bowel segment is called a sentinel loop. Sentinel loops are segments of intestine that persist relatively unchanged in size, shape, content, and position in serial radiographs. Often it is this static gas pattern that is first detected in patients with peritonitis. Pancreatitis is a common cause of localized peritonitis. It may lead to sentinel loops in the duodenum and transverse colon (Figures 4.17 and 4.48). Figure 4.17 Localized peritonitis. Lateral view of a dog abdomen depicting an area of hazy, indistinct serosal margins in the cranial abdomen (arrows). The margins are not well‐visualized due to regional inflammation caused by pancreatitis. The more caudal peritoneal serosal margins and the retroperitoneal margins remain distinct. Peritoneal effusion (or ascites) is free fluid in the peritoneal space. There are numerous possible etiologies (see differential diagnoses). Small volumes of fluid may be visible as streaks of soft tissue opacity mixed with intra‐abdominal fat. The fat provides the opacity interface to see the free fluid as thin, faint, curvy or “wispy” lines (Figure 4.18). “Fluid‐streaking of fat” tends to be easiest to see at the periphery of the abdominal cavity, where there are fewer superimposed structures. Sometimes a wet hair coat can mimic fluid‐streaking of fat, but wet hair extends beyond the limits of the abdominal cavity. Figure 4.18 Fluid‐streaking of fat. A. Lateral view of a cat abdomen depicting a small volume of peritoneal fluid. The fluid is interspersed with the fat to create wispy, curvilinear, soft tissue opacity streaks (arrow). B. Lateral view of a cat abdomen depicting a wet hair coat. The superimposed wet hair creates a similar pattern to (A), but the wet hair extends beyond the limits of the abdominal cavity (arrow). Peritoneal effusion is confined to peritoneal space. Larger volumes of peritoneal fluid lead to an overall increase in peritoneal opacity and greater effacement of serosal margins (Figure 4.19). The radiograph may appear underexposed. Examine the retroperitoneal space and the skeletal structures to determine whether the exposure was correct. In patients with peritoneal effusion, the small intestine often is suspended in the fluid and evenly distributed (unless displaced by a mass). Gas‐filled bowel loops rise to the top of the fluid and commonly collect in the mid‐abdomen. Severe peritoneal effusion can distend the abdomen and push the diaphragm cranially. In these cases the diaphragm may appear stationary in serial radiographs. Figure 4.19 Peritoneal effusion. Lateral view (A) and VD view (B) of a cat abdomen depicting a distended abdomen due to peritoneal fluid. The fluid completely effaces the borders of the peritoneal structures (liver, spleen, intestines, urinary bladder are not identified), but the borders of the kidneys remain visible because they are retroperitoneal (yellow arrows). A few gas‐filled segments of small intestine are depicted in the mid‐abdomen (black arrows). The retroperitoneal space remains normal as long as fluid is confined to the peritoneal space. The kidneys frequently are visible through the peritoneal effusion because they are surrounded by retroperitoneal fat. Retroperitoneal fluid typically is due to leakage of urine or blood, but can be caused by inflammation (see differential diagnoses). Fluid partially or completely obscures the margins of the kidneys and sublumbar muscles. Large volumes of fluid may distend the retroperitoneal space and displace the colon and small intestine ventrally (Figure 4.20). Peritoneal serosal margins remain distinct as long as the disease is confined to the retroperitoneal space. Figure 4.20 Retroperitoneal effusion. Lateral view of a dog abdomen depicting swelling in the retroperitoneal space due to fluid accumulation. The type of fluid cannot be determined from radiographs. The margins of the kidneys and sublumbar muscles are obscured. The descending colon and small intestine are displaced ventrally (arrows). Mineral opacity material is a frequent finding in the GI tracts of dogs and cats and may or may not be clinically significant. It may be associated with food, bones, or foreign objects. Focal mineral opacity structures outside the GI tract may represent calculi or dystrophic mineralization. These are seen more often in the hepatobiliary and urinary tracts. Some focal areas of mineral opacity appear to be free in the peritoneal cavity. These sometimes are Bates bodies, which appear as discrete, round, or oval‐shaped structures with smooth borders and less opaque centers (Figure 4.21). Bates bodies can vary in size and may be fixed in position or freely moveable, changing location in serial radiographs. They generally are considered incidental findings, possibly representing nodules of fat necrosis from a previous episode of pancreatitis or peritonitis. They are reported most often in older cats. Figure 4.21 Bates bodies (nodular fat necrosis). Lateral view (A) and VD view (B) of a cat abdomen depicting two mineral opacity nodules in the abdomen (arrows). The margins of the nodules are smooth and well‐defined and the centers are less opaque. Vascular mineralization is uncommon in dogs and cats. It typically appears linear and heterogenous (Figure 4.22) and may be associated with atherosclerosis or hypercalcemia. Mineralization usually involves the arteries (e.g., aorta, iliac, celiac, mesenteric). Figure 4.22 Vascular mineralization. Lateral view of a dog abdomen depicting mineral opacity foci in the retroperitoneal space consistent with mineralization in the wall of the abdominal aorta (arrows). May be mistaken for ureteral calculi. Metal opacity in the abdominal cavity may represent a foreign object (e.g., projectile, ingested foreign object), surgical implant (e.g., sutures, vascular band), or contrast medium. A mass in the abdominal cavity must be large enough or sufficiently different in opacity to be distinguished in radiographs. Soft tissue opacity masses generally need to be at least twice the width of the small intestine to be recognized. Larger masses may be identified by the displacement of the nearby structures, which is called a mass effect. A mass effect may be caused by any large, space‐occupying structure, including organomegaly, tumors, abscesses, cysts, granulomas, hematomas, and lipomas. Organomegaly may be physiologic or pathologic. Examples of physiologic organomegaly include a full urinary bladder, postprandial stomach, pregnancy, and compensatory renal hypertrophy (latter occurs when the other kidney is absent or not functional). Pathologic organomegaly is discussed with each specific organ later in this chapter. Clues to the origin of an abdominal mass come from its location and the direction of displacement of the adjacent viscera (Figure 4.23). Figure 4.23 Mass effect. Lateral view (A) and VD view (B) of a dog abdomen depicting the possible sites of origin for an intra‐abdominal mass based on its location and the direction of displacement of the adjacent structures (yellow arrows). Most masses are soft tissue opacity (Figure 4.24), but long‐standing and necrotic masses can mineralize or cavitate, the latter sometimes filling with gas. Some neoplastic masses are bone‐forming. Figure 4.24 Intra‐abdominal mass. Lateral view (A) and VD view (B) of a dog abdomen depicting a soft tissue opacity mass in the mid‐abdomen. The mass displaces the intestines dorsally, caudally, and to the right (black arrows). The transverse colon and stomach are displaced cranially (white arrows). The edges of the mass are well‐defined by intra‐abdominal fat (yellow arrows). Possible origins for this mass include spleen, mesentery, intestine, left kidney. This was a tumor in the left kidney. The margins of a mass may be well‐defined or indistinct, depending on the opacity interface. Indistinct margins may result from visceral crowding or adjacent fluid, the latter due to inflammation, hemorrhage, or effusion. When a large volume of intra‐abdominal fluid is present the radiographs should be repeated after removing as much fluid as possible to better visualize the visceral margins. Lymphadenomegaly may be caused by neoplasia, infection, or inflammation and can produce a visible intra‐abdominal mass. Groups of enlarged visceral lymph nodes sometimes blend together to produce an ill‐defined, soft tissue opacity mass in the peritoneal space (Figure 4.25). Sublumbar lymphadenomegaly most often involves the medial iliac lymph nodes. It typically appears as a retroperitoneal mass ventral to the caudal lumbar spine. Figure 4.25 Abdominal lymph node enlargement. Lateral view (A) and VD view (B) of a dog abdomen depicting organomegaly and lymphadenomegaly due to lymphoma. The liver (L) and spleen (S) are enlarged with rounded margins. The mesenteric lymph nodes (black arrow) and sublumbar lymph nodes (white arrow) are enlarged. B = urinary bladder. Enlargement of the sublumbar lymph nodes may be accompanied by a periosteal response along the caudal lumbar vertebrae. Periosteal new bone sometimes involves the pelvic bones and proximal femurs but most often develops along the middle ventral borders of the L5‐7 vertebral bodies (Figure 4.26). This new bone production differs from spondylosis deformans. Spondylosis tends to be better‐defined and forms at the ends of the vertebral bodies, not in the middle. Figure 4.26 Periosteal response. Lateral view of a dog abdomen depicting medial iliac lymphadenomegaly (white arrow) and a periosteal response along the caudal lumbar vertebrae (black arrows). The liver is located in the cranial abdomen. It is connected by ligaments to the diaphragm, caudal vena cava, stomach, duodenum, and right kidney. The falciform ligament attaches the liver to the ventral body wall and serves as a storage reservoir for fat. The liver consists of six lobes: right lateral, left lateral, right medial, left medial, caudate, and quadrate (Figure 4.27). The gall bladder lies between the quadrate lobe and the right medial lobe. It is not visible in radiographs unless enlarged, emphysematous, mineralized, or filled with contrast medium. The right kidney lies in the renal fossa of the caudate liver lobe. Because the kidney and the liver are the same opacity, the cranial pole of the right kidney may not be visible unless surrounded by fat or gas. Figure 4.27 Liver anatomy. Lateral view (A) and VD view (B) of a dog abdomen illustrating the individual liver lobes, gall bladder (GB), stomach, and right kidney. In the lateral view, the left lateral and right medial liver lobes form the caudoventral edge of the liver. The triangular‐shaped liver is located between the diaphragm and the ventral body wall (Figures 4.2 and 4.3). Its margins normally are even and well‐defined. The cranial border of the liver blends with the caudal border of the diaphragm (Both are soft tissue opacity with no other opacity between them). The dorsal liver border is formed by the caudate lobe, but it is not well visualized because it blends with the adjacent soft tissues. The caudal border of the liver is adjacent to the stomach and also poorly visualized. The ventral liver border usually is visible because it is adjacent to falciform fat. The caudoventral border of the liver forms an acute angle at about the level of the costal arch. The costal arch is the curved line formed by the caudal costal cartilages (Figure 4.28). The caudoventral edge of the liver is a frequently used landmark to evaluate liver size. When the edge extends caudal to the costal arch, the liver commonly is considered to be enlarged. However, this interpretation of liver size is based on palpation of the liver in a clinical setting. It is important to realize that palpable findings do not always correlate with radiographic findings. The costal arch is typically mineral opacity. It is located cranial to the palpable arch because muscle, skin, and subcutaneous tissue are between the true arch and the fingers during palpation. In radiographs, of normal dogs and cats, the caudoventral edge of the liver frequently extends caudal to the visible costal arch. This is usually evident during inspiration and in right lateral recumbency. The liver may also extend further caudal than expected in animals with weak supporting ligaments (e.g., old age, endocrinopathy). Do not rely on the position of the caudoventral edge of the liver to diagnose hepatomegaly. The key radiographic finding with hepatomegaly is rounding of the liver margins. Figure 4.28 Liver size. Lateral view (A) and VD view (B) of a dog cranial abdomen with the liver and stomach highlighted. In the lateral view, the caudoventral edge of the liver (white arrow) extends to about the level of the costal arch (yellow dotted line). The normal gastric axis (black dashed lines) is angled somewhere between perpendicular to the spine and parallel with the ribs. In general, if the pylorus is more cranial than perpendicular to the spine, the liver is considered small. If the pylorus is further caudal than parallel to the ribs, the liver is considered enlarged. In the VD view, the normal gastric axis is about perpendicular to the spine. Liver size is also assessed in a lateral view by evaluating the position of the gastric axis. The gastric axis is an imaginary line drawn between the fundus and pylorus of the stomach (Figure 4.28). In a lateral view, the normal gastric axis is somewhere between perpendicular to the spine and parallel with the ribs, depending on the patient’s body conformation and the size of the stomach. The gastric axis tends to be more perpendicular to the spine in deep‐chested dogs (e.g., Afghan Hound, Collie) and in patients with a full stomach. It often is more parallel with the ribs in shallow‐chested breeds (e.g., Bulldog, Pug) and in patients with an empty stomach. The gall bladder in a lateral view is located in the cranioventral part of the liver. Mineral or gas opacity in this area may be associated with the gall bladder. However, artifacts created by superimposition of the ribs, costal cartilages, and the caudal lung lobes must be differentiated from a hepatobiliary lesion. A large gall bladder can create a convex, soft tissue opacity bulge along the ventral border of the liver, particularly in cats (Figure 4.29). Figure 4.29 Large gall bladder. Lateral view of a cat abdomen depicting a soft tissue opacity bulge along the ventral border of the liver due to a large gall bladder (arrow). The liver occupies the space between the diaphragm and the stomach. In dogs, the liver is relatively symmetrical in shape, occupying at least two intercostal spaces on both the right and left sides. The gastric axis tends to be nearly perpendicular to the spine (Figure 4.28), but it is less reliable for assessing liver size in a VD/DV view than in a lateral view. In cats, there usually is more liver on the right side than on the left. In both dogs and cats, the gall bladder is located right of midline in the cranial part of the liver. The liver normally lies within the costal arch. Its position can vary somewhat depending on the patient’s body conformation and phase of respiration. Again, the liver tends to be positioned further cranially in deep‐chested patients and more caudal in patients with a wide, shallow thorax. Displacement of the liver may be due to a mass effect or loss of abdominal integrity. Cranial displacement of the liver most often results from a hernia or rupture of the diaphragm. This is because the cranial position of the liver is limited by an intact diaphragm. A large intra‐abdominal mass can push both the liver and diaphragm cranially (e.g., distended stomach, advanced pregnancy, severe splenomegaly). Caudal displacement usually is due to an expanded thoracic cavity (e.g., severe pleural effusion, severe pneumothorax). Weakening of the supportive ligaments along the ventral body wall can lead to a pendulous abdomen that allows the liver to move caudally. Ligaments frequently weaken and stretch in older animals and in patients with hypercortisolism. Lateral or ventral displacement of the liver usually is due to loss of body wall integrity, which may result from trauma or a congenital abnormality. Dorsal displacement is caused by a ventral mass effect. In patients with a large amount of falciform fat, the liver may appear to be dorsally displaced (Figure 4.30). Figure 4.30 Falciform fat. Lateral view of a cat abdomen depicting a large amount of fat in the falciform ligament (arrow). The liver appears to be displaced dorsally (or perhaps the body wall is ventrally displaced). As mentioned earlier, liver size is assessed by the shape and position of its caudoventral edge and the position of the gastric axis. Describing a liver as small often is a subjective assessment. Enlargement of the liver is recognized by the rounding of the hepatic margins, caudal extension of the liver edge and caudal displacement of the stomach. Unless the change is severe, the diagnosis of a small liver or a large liver can be difficult from radiographs. The causes and radiographic signs of each are discussed in more detail on the following pages. In general, a liver that occupies fewer than 2 intercostal spaces is considered small (Figure 4.31). In a lateral view, the caudoventral edge of the liver does not extend to the costal arch. The gastric pylorus may be located cranial to the fundus, making the gastric axis slope from caudodorsal‐to‐cranioventral. The most common causes of microhepatia are a portosystemic vascular shunt and hepatic cirrhosis. Figure 4.31 Microhepatia. Lateral view (A) and VD view (B) of a dog abdomen depicting a small liver. There are fewer than two intercostal spaces between the stomach and the diaphragm. The caudoventral edge of the liver (white arrow) does not extend to the costal arch. In the lateral view, the gastric axis slopes from caudodorsal‐to‐cranioventral (black dotted line). A portosystemic vascular shunt is an abnormal communication between the portal vein and the systemic circulation. The shunt may be congenital or acquired, partial or complete, intra‐hepatic or extra‐hepatic. In all of these, blood from the portal system is allowed to bypass the liver. In radiographs, the liver is small, but the hepatic margins usually remain even and well‐defined. The kidneys may be large to compensate for the underperforming liver. Hepatic cirrhosis is scarring and fibrosis of the liver due to chronic inflammation. In radiographs, the liver is small with irregular margins, the latter due to nodular regeneration. Hepatic cirrhosis frequently progresses to liver failure and peritoneal effusion. Radiographic diagnosis of microhepatia is easier when the entire liver is small and less obvious when only a portion of the liver is affected. Venous portography can be used to investigate a suspected portosystemic shunt (Figure 4.32). Hepatic vessels will be poorly opacified if there is severe shunting of blood. The procedure for venous portography, as well as its indications and contraindications, is described in the Contrast Radiography section of Chapter 2. Figure 4.32 Portosystemic vascular shunt. Lateral views of a dog abdomen depicting venous portograms. A. Normal study: contrast medium is infused via a catheter (white arrow) that was surgically placed in a jejunal vein (black arrow). Contrast medium flows through the jejunal vein and into the portal vein (PV), which leads to opacification of multiple intra‐hepatic branches. B. Portosystemic shunt: contrast medium flows from the portal vein directly into the caudal vena cava (CVC). The intra‐hepatic shunt (yellow arrow) allows most of the contrast medium to bypass the intra‐hepatic branches and enter the right ventricle (RV) and main pulmonary artery (MPA). Hepatomegaly may involve part or all of the liver. Partial liver enlargement usually is due to a mass. Generalized enlargement may be due to endocrinopathy, venous congestion, inflammation, or neoplasia (see differential diagnoses). In a lateral radiograph of a patient with generalized hepatomegaly, the caudoventral edge of the liver is rounded and extends a significant distance caudal to the costal arch (Figures 4.33 and 4.34). The stomach is displaced caudally and dorsally, producing a more craniodorsal‐to‐caudoventral slope to the gastric axis. The severity of stomach displacement depends on the degree of liver enlargement. Severe hepatomegaly can also push the proximal duodenum, right kidney, and transverse colon further caudally and may limit movement of the diaphragm. Figure 4.33 Rounding of liver margins. Lateral views of a dog abdomen depicting a normal size liver (A) and an enlarged liver (B). The caudoventral edge of the normal liver forms an acute angle (less than 90°) near the costal arch. Hepatomegaly causes rounding of the caudoventral edge and extends the edge caudal to the costal arch. Figure 4.34 Hepatomegaly. Lateral view (A) and VD view (B) of a dog abdomen depicting generalized liver enlargement. The borders of the liver are rounded (arrows). In the lateral view, the caudal edge of the liver extends significantly caudal to the costal arch. The stomach is displaced caudally and dorsally. The gastric pylorus is caudal to the fundus, altering the slope of the gastric axis (black dotted line). Generalized hepatomegaly often is accompanied by a distended abdomen, either due to the large size of the liver, a weak body wall, enlargement of other viscera, or peritoneal effusion. Venous congestion and infiltrative diseases such as lymphoma frequently lead to enlargement of multiple organs and varying amounts of peritoneal effusion. Masses growing in or on the liver generally lead to asymmetric hepatomegaly and an abnormal liver shape. The adjacent viscera may be unevenly displaced, depending on the size and location of the mass (Figure 4.35). A left liver mass can displace the gastric fundus caudally and medially, sometimes pushing the fundus caudal to the pylorus. The head of the spleen and the intestines may be pushed caudally. Right liver enlargement can displace the gastric pylorus, proximal duodenum, and right kidney caudally and medially. Figure 4.35 Liver mass. Two VD views of a dog abdomen depicting asymmetric liver enlargement. Where the liver is enlarged, its margin is rounded. A. A mass in the right side of the liver displaces the gastric pylorus and duodenum caudally and to the left (black dotted arrows). The duodenum is highlighted for demonstration purposes. The right kidney is displaced caudally (white dotted arrow). B. Left liver enlargement displaces the gastric fundus to the right and caudally (black dotted arrow) and pushes the spleen and left kidney caudally (white arrows). A centrally located liver mass may displace the gastric pylorus caudally and dorsally (Figure 4.36). A central hepatic mass can extend caudal to the stomach, particularly if it is pedunculated, and may appear separate from the liver. In these cases, the liver mass may be misdiagnosed as part of the spleen or other nearby structure. Figure 4.36 Central liver mass. Lateral view of a dog abdomen depicting a soft tissue opacity mass in the cranioventral abdomen (black arrows). The mass displaces the gastric pylorus caudally and dorsally (white dotted arrow) and pushes the intestines caudally. A mass in this area may be associated with the liver, stomach, spleen, or pancreas. In addition to mistaking a hepatic mass for part of the spleen, the spleen may be mistaken for part of the liver. In a lateral view the tail of the spleen sometimes blends with the caudoventral edge of the liver, mimicking a large liver. In these cases the opposite lateral view often allows the liver and spleen to be distinguished as separate structures. A large gall bladder may produce an intra‐hepatic mass effect. As mentioned earlier, gall bladder distention may produce a swelling or bulge along the ventral liver border in a lateral view (Figure 4.29). The normal liver is uniform soft tissue opacity. Mineral or gas opacity in the liver is abnormal and frequently involves the biliary system. Occasionally, dystrophic mineralization or a gas‐producing bacterial infection occurs in a long‐standing hepatic tumor or abscess, or in an area of liver necrosis (e.g., liver lobe torsion). Gas also can enter the liver parenchyma from the GI tract via the portal system, which may occur due to a necrotic stomach (e.g., gastric dilatation and volvulus). Abnormal opacity in the liver parenchyma typically appears as an irregular or mottled pattern localized in part of the liver. Abnormal opacity in the gall bladder is seen in the right cranioventral part of the liver. An emphysematous gall bladder most often is associated with diabetes mellitus. Gas initially forms in the bladder wall and eventually fills the lumen to produce multiple tiny bubbles that conform to the shape of the gall bladder (Figure 4.37). Emphysema can extend into the bile ducts to create a tree‐like pattern of gas opacity, similar in appearance to air bronchograms in consolidated lungs. Figure 4.37 Emphysematous gall bladder. Lateral view (A) and VD view (B) of a dog abdomen depicting localized gas opacity in the right cranioventral part of the liver (arrow). The gas is in the shape and location of the gall bladder. Mineral opacity in the gall bladder or bile ducts may represent cholelithiasis or dystrophic mineralization. Choleliths (gallstones) can vary greatly in size, number, and opacity (Figure 4.38). They may or may not be clinically significant. Not all gallstones are mineral opacity. When in the common bile duct, mineral opacity calculi are called choledocoliths and may be visible between the gall bladder and the duodenum (Figure 4.38). Mineralization of the gall bladder wall typically appears as a thin, well‐defined, shell‐like structure (Figure 4.39). Mineralization in the bile ducts appears as a linear or branching pattern in either an isolated part of the liver or scattered throughout the liver (Figure 4.40). Figure 4.38 Cholelithiasis. Lateral view (A) and VD view (B) of a dog abdomen depicting multiple, small, mineral opacity structures in the shape and location of the gall bladder (white arrow). There also is a focal mineral opacity located between the gall bladder and the duodenum, consistent with a choledocolith (black arrow). Figure 4.39 Mineralization of the gall bladder wall. Lateral view (A) and VD view (B) of a dog abdomen depicting a thin, shell‐like, mineral opacity structure in the area of the gall bladder (arrow); sometimes called a “porcelain” gall bladder. Figure 4.40 Bile duct mineralization. Lateral view (A) and VD view (B) of a dog abdomen depicting a branching pattern of heterogeneous mineral opacity structures in the liver (arrows), typical of biliary mineralization. The spleen is a relatively flat and elongated organ with even, well‐defined margins. The edges of the spleen form acute angles (less than 90°). Because it is thin, the spleen often is difficult to identify in radiographs except where it overlaps or “folds” on itself. In these areas the spleen is essentially doubled in thickness and opacity. The two layers of spleen summate to create a triangular or wedge‐shaped appearance (Figure 4.41). Seeing a splenic triangle in a radiograph does not mean you have identified the entire spleen; rather, you have found the starting point to begin examining the spleen. Figure 4.41 Normal spleen. Right lateral view (A), left lateral view (B), and VD views (C and D) of a dog abdomen illustrating some of the normal positions of the spleen. Overlap of the head and body of the spleen produces a wedge‐shaped soft tissue opacity structure in the left craniodorsal abdomen (black arrow). Overlap of the body and tail can create a similar wedge shape in the ventral abdomen (white arrow). For descriptive purposes, the spleen is divided into three parts; head, body, and tail. The head is the proximal part of the spleen that is anchored to the fundus of the stomach by the gastrosplenic ligament. The body of the spleen is the middle part. The tail of the spleen is the distal part. Both the body and tail of the spleen are freely moveable. In dogs, the body and tail can vary considerably in size and position. In cats, they are more constant and proportionately smaller than in dogs. The head of the spleen is located in the craniodorsal abdomen. Overlap of the head and body of the spleen creates a soft tissue opacity triangle between the fundus of the stomach and the kidneys (Figure 4.41). This triangle commonly is called the “head of the spleen,” but it represents only a portion of the proximal spleen. The triangle sometimes is difficult to identify in a lateral view because it blends with the adjacent soft tissues. In cats and overweight dogs the triangle may be more distinct because it is surrounded by fat. The body and tail of the spleen can extend anywhere from the liver to the urinary bladder. Overlap of body and tail often creates a soft tissue opacity triangle in the ventral abdomen, particularly in a right lateral view. The distal spleen is easiest to see when it is positioned near the ventral body wall, which is common in dogs but rare in cats. In many cats, the normal spleen is not identified in a lateral view. The head of the spleen is located in the left cranial abdomen. Again, overlap with the body of the spleen produces the familiar soft tissue opacity triangle near the left body wall, located just caudal to the gastric fundus and cranial to the left kidney (Figure 4.41). As we discussed with the lateral view, this triangular‐shaped overlap is not the “head of the spleen”; rather, it is a starting point from which to begin evaluating the spleen. The distal spleen can extend either caudally along the left body wall or toward the mid‐abdomen. Its margin tends to be difficult to trace in a VD/DV view because the other viscera are superimposed. With careful inspection, however, the entire spleen often can be identified. Non‐visualization of the spleen may be due its absence (e.g., prior splenectomy) or because it is obscured. The spleen may be obscured because it is small and blends with other soft tissue structures or because there is no opacity interface (e.g., visceral crowding, loss of body fat, adjacent fluid accumulation). Displacement of the spleen can occur in a variety of directions. The body and tail of the spleen are quite mobile and readily displaced by nearby structures or loss of body wall integrity. The position of the head of the spleen is largely determined by the size and orientation of the stomach because the two are connected by the gastrosplenic ligament. In a deep‐chested dog with an empty stomach, the proximal spleen may lie near the diaphragm. Gastric dilatation with volvulus or a splenic torsion can displace the proximal spleen so that it is absent from its expected position in the craniodorsal abdomen. Unless it is very large, describing the size of the spleen tends to be a subjective assessment. Splenomegaly frequently is over‐diagnosed, especially when a long portion of the spleen is visible or the tail of the spleen extends further caudally than expected. The normal spleen is relatively large in certain dog breeds (e.g., German Shepherd, Greyhound). The key radiographic finding with splenomegaly, as with hepatomegaly, is rounding of the margins (Figure 4.42). Splenic enlargement may be generalized or localized. There are numerous causes of generalized splenomegaly (see differential diagnoses). A large spleen may displace the intestines dorsally, caudally, and either to the right or left side. Irregular or uneven splenic borders suggest multiple nodules or masses in the spleen. Figure 4.42 Splenomegaly. Lateral view (A) and VD view (B) of a cat abdomen depicting generalized enlargement of the spleen (arrows). The margins of the spleen are rounded. The small intestine is displaced caudally and to the right. Localized splenomegaly is due to a splenic mass. A mass in the proximal spleen typically produces increased opacity in the left craniodorsal abdomen and causes rounding of the splenic triangle. Larger masses can deform or medially displace the gastric fundus and push the left kidney caudally. Masses in the body and tail of the spleen are much more variable in position. They are seen most often in the ventral mid‐abdomen (Figure 4.43). Figure 4.43 Splenic mass. Lateral view (A) and VD view (B) of a dog abdomen depicting a rounded, soft tissue opacity mass in the ventral mid‐abdomen (arrows). The adjacent bowel is displaced caudally, dorsally, and to the right. The mass may originate from spleen, mesentery, lymph node, or intestine. Peritoneal effusion is a frequent finding with both benign and malignant causes of splenic enlargement. The type of fluid cannot be determined from radiographs, but often it is non‐clotting blood. Depending on the volume of fluid, peritoneal serosal margins may be obscured. Repeating the radiographs after removing as much fluid as possible may yield additional diagnostic information. It often is difficult to determine from radiographs whether a mass in the area of the spleen actually involves the spleen. Masses in the left craniodorsal abdomen, for example, may originate in the left kidney or adrenal gland. Masses in the mid‐abdomen may originate from the mesentery, lymph node, or intestine. A smaller than expected spleen may be due to hypovolemia or atrophy, the latter reported most often in aged animals. The feline spleen tends to be proportionately smaller than the canine spleen, but not always. It has been suggested that a feline spleen that is visible in a lateral radiograph must be enlarged; however, just because it is visible does not necessarily mean that the spleen is abnormally large. Rotation of the spleen around its mesenteric axis often is associated with gastric dilatation and volvulus, but may occur independently. Splenic torsion is a rare but potentially life‐threatening condition, most often reported in large, deep‐chested dogs. Rotation restricts splenic blood flow leading to venous congestion, ischemia, and moderate to severe splenomegaly. The classic radiographic finding is a caudally and medially displaced spleen with a reverse C‐shaped appearance (Figure 4.44). This finding, however, may not be apparent unless the spleen is significantly enlarged. In most cases of splenic torsion, the proximal spleen is absent from its expected position in the left craniodorsal abdomen. Pockets of gas sometimes are visible in a rotated spleen due to secondary infection with gas‐producing bacteria (Figure 4.45). Figures 4.44 Splenic torsion. Lateral view (A) and VD view (B) of a dog abdomen depicting an enlarged spleen that is displaced medially and caudally (yellow arrows). The shape of the spleen resembles a reverse capital letter C. The splenic triangle is absent from its normal location in the left craniodorsal abdomen (white arrow). Figure 4.45 Splenic emphysema. Lateral view of a dog abdomen depicting a soft tissue opacity mass in the cranioventral abdomen (black arrow) with multiple foci of gas opacity (white arrow). Gas most likely is due to gas‐producing bacteria. The mass may represent a splenic torsion or an abscess associated with the spleen, liver, pancreas, intestine, or mesentery. The normal spleen is homogenous soft tissue opacity. Gas or mineral opacity in the spleen is abnormal and may be focal or multifocal. Gas in the spleen (splenic emphysema) is rare, most often associated with splenic torsion and a secondary gas‐producing bacterial infection (Figure 4.45). Splenic emphysema typically appears as a patchy, mottled, or “foamy” gas pattern. Gas in a splenic blood vessel may produce an “air vasculogram,” similar in appearance to an air bronchogram in consolidated lungs. Mineralization in the spleen usually is dystrophic and may result from chronic inflammation or infection. Neoplastic mineralization can occur (e.g., extra‐skeletal osteosarcoma). The pancreas is divided into three parts; right limb, left limb, and body. The body is the part between the two limbs and it is located in the right cranial abdomen near the gastroduodenal angle (Figure 4.46). The gastroduodenal angle refers to the junction between the stomach and the duodenum. Figure 4.46 Pancreas. Lateral view (A) and VD view (B) of a dog abdomen with the area of the pancreas highlighted. The body of the pancreas lies in the gastroduodenal angle (black dotted arrow). The right pancreatic limb (R) lies adjacent to the descending duodenum (yellow arrowheads). The left pancreatic limb (L) lies adjacent to the greater curvature of the stomach (black arrowheads). The right limb of the pancreas extends caudally from the body of the pancreas to about the level of the L3‐4 vertebrae. It is positioned between the descending duodenum and the ascending colon. The left pancreatic limb extends transversely from the body, across midline, and toward the left kidney. It is positioned between the greater curvature of the stomach and the transverse colon. The normal pancreas seldom is seen in radiographs due to its small size and similar opacity to the adjacent tissues. When surrounded by fat, the left pancreatic limb may be visible in a VD/DV view, particularly in cats (Figure 4.47). In these cases it appears as a thin, linear, soft tissue opacity structure within a triangle formed by the stomach, spleen, and left kidney. Figure 4.47 Normal pancreas. VD view of a cat abdomen depicting the left limb of the pancreas (arrow). The left limb is visible within the triangle formed by the stomach, spleen, and left kidney because it is surrounded by fat. Diseases of the pancreas may or may not be evident in radiographs. Characteristic findings of pancreatic disease include increased opacity, indistinct serosal margins, and a mass effect in the area of the pancreas (Figure 4.48). These findings may be present near the gastroduodenal angle or along the descending duodenum or caudal to the stomach. Note: when examining these areas, use caution when interpreting subtle increases in opacity and mildly indistinct margins. In a VD view of many patients there is less fat and more visceral crowding in the right cranial abdomen than in the left cranial abdomen. Figure 4.48 Pancreatic disease. Lateral view (A) and VD view (B) of a dog abdomen depicting increased opacity and indistinct serosal margins in the area of the pancreas. The gastroduodenal angle is widened (black double‐headed arrow); there is soft tissue swelling between the greater curvature of the stomach and the transverse colon (white arrow), and there are static gas patterns (sentinel loops) in the descending duodenum and transverse colon (yellow arrows). A mass effect in the area of the pancreas may be caused by pancreatic swelling or a pancreatic mass (e.g., tumor, cyst, abscess). Both pancreatitis and pancreatic neoplasia produce similar radiographic signs and cannot reliably be differentiated. In a VD view, a pancreatic mass effect may displace the duodenum to the right and widen the gastroduodenal angle. The transverse colon may be displaced caudally, resulting in increased distance from the stomach. In a lateral view, the duodenum may be displaced either ventrally or dorsally. Pancreatic diseases can cause a regional peritonitis that diminishes peristalsis in the nearby intestines. Regional inflammation near the descending duodenum or transverse colon may lead to a localized functional ileus known as a sentinel loop. A sentinel loop is a static segment of bowel, often recognized in radiographs by its static gas pattern that remains relatively unchanged in serial radiographs. The segment appears similar in size, shape, and content between images. Sentinel loops do not only occur with pancreatitis; any site of peritoneal inflammation can lead to a functional ileus. Pancreatic disease can progress to a more diffuse peritonitis and peritoneal effusion, further obscuring serosal margins. Pancreatic adenocarcinoma can metastasize throughout the peritoneal space to produce a diffuse, mottled, hazy pattern (i.e., carcinomatosis). Severe pancreatic disease may cause a gastric outflow problem and persistent distention of the stomach. It can also lead to hepatitis and hepatic lipidosis. Pancreatic mineralization is rare but may result from chronic inflammation or fat necrosis. Normal radiographs do not rule out pancreatic disease. Follow‐up radiographs or other imaging modalities may be needed in patients that do not respond to appropriate therapy. Signs of pancreatic disease sometimes are evident in an Upper GI study. Radiographic signs may include a duodenal sentinel loop, delayed gastric emptying, delayed transit through the intestines, or thickening of the duodenal or gastric wall. The GI tract includes the stomach, small intestine, and large intestine. The esophagus is part of the alimentary tract and is discussed in Chapter 3: Thorax. Normal GI structures are continuously in motion. A radiograph depicts their appearance only at a single instant in time. Multiple views, serial radiographs, and contrast radiography may be needed to detect or confirm lesions. Many GI diseases present with similar signs and any particular disorder can vary significantly in its radiographic appearance. Most GI findings are not pathognomonic for any specific condition. Some diseases of the GI tract rarely produce detectable radiographic abnormalities (e.g., parasitic diseases, dietary problems, GI inflammation). Radiography generally is a readily available diagnostic imaging modality and can provide information about the GI tract relatively rapidly. Other modalities, however, may be needed for a more definitive diagnosis, including endoscopy, ultrasonography, and computed tomography. The stomach is located caudal to the diaphragm and liver. Its caudal border is convex and called the greater curvature. Its cranial border is concave and called the lesser curvature (Figure 4.49). For descriptive purposes, the stomach is divided into four parts: cardia, fundus, body, and pylorus. Figure 4.49 Anatomy of the stomach. VD view of a dog abdomen illustrating the parts of the stomach and the rugal folds. The cardia is the small area of the stomach that joins the esophagus. It is not radiographically distinct from the fundus. The fundus is the dome‐shaped pouch that comprises the dorsal and left lateral portions of the stomach. It stores undigested food and gas. The body of the stomach is the large distensible part located between the fundus and the pylorus. The pylorus forms the distal third of the stomach. It consists of the pyloric antrum (the area before the gastric outlet), the pyloric canal (the passage that connects the stomach to the duodenum), and the pyloric sphincter (a thick muscular ring that helps regulate outflow from the stomach). In most adult dogs, the pylorus is positioned ventral to the fundus and to the right of midline. In cats, puppies, and barrel‐chested dogs, the pylorus tends to be closer to midline. The closer the pylorus is to midline, the more U‐shaped or J‐shaped the stomach appears in a VD/DV view (Figure 4.50). Figure 4.50 Normal stomach. VD views of a dog abdomen (A) and a cat abdomen (B) with the stomach highlighted to show the relative positions of the esophagus (E), cardia (C), fundus (F), body (B), pyloric antrum (PA), pyloric canal (PC), and duodenum (D). The size, shape, position, and opacity of the stomach can vary significantly depending on its contents. An empty stomach generally lies within the costal arch, rarely extending caudal to the last pair of ribs. As the stomach fills, the fundus and body expand and the greater curvature becomes more convex. Filling increases the length and diameter of the pylorus and moves it further to the right. In a lateral view, a full stomach may touch the ventral body wall and extend caudally to the level of the umbilicus. The stomach is able to expand because the gastric mucosa is formed into folds called rugae. The rugal folds generally are larger and more numerous in dogs than in cats and often more visible in the fundic region (Figure 4.49). Rugal folds can vary significantly in appearance and their radiographic interpretation requires experience and excellent visualization of the gastric mucosa. In general, each fold should be similar in height and width (thickness) to the width of the spaces between folds. The mucosal margin of the stomach rarely is identified with certainty in survey radiographs, because fluid and most ingesta are the same opacity as the mucosa, contrast radiography is usually needed. Prior to performing gastrography, however, always make four view survey radiographs of the stomach: right lateral, left lateral, VD, and DV. In many cases, these four views will redistribute gas and fluid in the stomach lumen and will help clarify questionable findings. Four views are also important during gastrography to allow different parts of the stomach to fill with contrast medium. This is particularly useful when searching for mural lesions and identifying the different parts of the stomach. In some animals, especially overweight cats, a submucosal layer of fat may be visible in the stomach wall. Submucosal fat appears as a thin line of fat opacity that follows the curvature of the stomach (Figure 4.51). The fat layer may be mistaken for gas in the stomach wall. Figure 4.51 Gastric submucosal fat. VD view of a cat abdomen depicting a thin line of submucosal gastric fat (arrow). In most patients, the stomach contains some gas or food, making its identification relatively simple. The distribution of material in the stomach varies with its volume and the position of the patient at the time of radiography. Gas generally rises to the highest parts of the stomach and fluid flows with gravity into the dependent parts. Deliberately changing the position of the patient is useful to redistribute gas, fluid, and contrast media in the stomach. In situations where there is only a small volume of material in the stomach, the patient should be rotated a full 180° for a few seconds and then back to the position desired to ensure the gas or fluid moves to a different part of the stomach. Figures 4.52–4.55 illustrate the distribution of fluid and gas in the stomach based on the position of the patient. Each figure includes both a radiograph and a cross‐sectional CT image to help describe the appearance of the stomach in right lateral, left lateral, dorsal and ventral recumbencies. Table 4.1 summarizes the distribution of gas and fluid in different parts of the stomach. Figure 4.52 Stomach in right lateral view. CT image (A) and lateral radiograph (B) depicting a dog in right lateral recumbency. S = spine. Fluid flows into the dependent pylorus and gas rises into the fundus. In the radiograph, a fluid‐filled pylorus may appear as a discrete, round, soft tissue opacity mass in a right lateral view (arrows), which may be mistaken for pathology. As shown in Figure 4.53, the left lateral view allows gas to enter the pylorus, confirming its identity. Figure 4.53 Stomach in left lateral view. CT image (A) and lateral radiograph (B) depicting a dog in left lateral recumbency. S = spine. Fluid flows into the dependent fundus and gas rises into the pylorus. Gas is more likely to enter the duodenum while in left lateral recumbency (black arrows) The body of the stomach may contain fluid or gas, depending on the volume of each. Figure 4.54 Stomach in VD view. CT image (A) and lateral radiograph (B) depicting a dog in dorsal recumbency. S = spine. Fluid flows into the dependent fundus and gas rises into the body. The pylorus may contain fluid or gas, depending on the volume of each. Figure 4.55 Stomach in DV view. CT image (A) and lateral radiograph (B) depicting a dog in ventral recumbency. S = spine. Fluid flows into the dependent body of the stomach and may fill the pylorus, depending on volume. Gas rises into the fundus and may partially fill the pylorus. Table 4.1 Typical distribution of gas and fluid in the stomach The normal position of the stomach is influenced by the volume of its contents as well as the patient’s body conformation and the phase of respiration. For example, in deep‐chested dogs the stomach tends to be more cranial in position than in barrel‐chested dogs. The stomach naturally moves caudally during inspiration and cranially during expiration. Abnormal position of the stomach may be due to a nearby mass effect or a hernia (see differential diagnoses). The cardia is the least mobile part of the stomach because it is relatively fixed in position by its attachment to the esophagus. A largely distended stomach may be physiologic or pathologic. Follow‐up radiographs sometimes are needed to distinguish the two. Recent ingestion of a large amount of food or water can lead to marked gastric distention (Figure 4.56). Ingestion of a large amount of foreign material can produce a similar appearance (Figure 4.57). Because normal and abnormal gastric contents can appear similar in radiographs, a follow up study often is useful. A stomach that can empty normally will naturally be smaller in follow‐up radiographs, provided the patient does not eat, drink, or vomit between studies. Figure 4.56 Gastric distention due to overeating. Lateral view (A) and VD view (B) of a dog abdomen depicting a stomach greatly distended with heterogeneous material (arrows). In this case, the material is ingested food, which was confirmed by seeing a smaller stomach and feces in the colon in follow‐up radiographs. Figure 4.57 Gastric distention due to foreign material. Lateral view (A) and VD view (B) of a dog abdomen depicting a stomach greatly distended with heterogenous material (arrows). In this case, the material ingested is polyurethane, which is an adhesive agent that expands and hardens when in water (e.g., “Gorilla glue”). Follow‐up radiographs documented a lack of emptying. Disorders that prevent normal gastric emptying may be physical or functional, congenital or acquired, acute or chronic, partial or complete. Physical obstructions can result from foreign material, thickening of the stomach wall, or gastric malpositioning. Functional outflow problems usually are due to pyloric disease. The degree of gastric distention depends on the severity and duration of the disorder and the patient’s ability to vomit. A stomach that is largely distended has been described as both dilated and dilatated. The terms often are used interchangeably. Specifically, dilation refers to the passive act of enlarging whereas dilatation describes the state of abnormal enlargement. Dilatation is dilation beyond normal dimensions. Gastric dilatation sometimes is called gastric bloat. A largely distended stomach creates a mass effect in the cranial abdomen. The intestines, spleen, and sometimes the kidneys often are displaced caudally. An extremely distended, mostly fluid‐filled stomach may be difficult to recognize in radiographs because it is homogenous in opacity and its margins extend much further caudally than expected (Figure 4.58). A gas pocket floating on top of the gastric fluid may be mistaken for the actual size of the stomach if the fluid‐filled portion is not identified. Figure 4.58 Chronic gastric outflow obstruction. Lateral view (A) and VD view (B) of a dog abdomen depicting a greatly distended, mostly fluid‐filled stomach. A gas bubble in the fundus (white arrow) may be mistaken for the entire size of the stomach if the fluid‐filled caudal part is not identified (black arrows). In the lateral view, the gravel sign is visible in the pyloric region (yellow arrow). In patients with a chronic gastric outflow problem, multiple, tiny, mineral opacity objects may be visible in the dependent portion of the stomach (Figure 4.58). This finding is called the gravel sign. The gravel sign can occur anywhere in the GI tract. It results from the sand‐like sedimentation of heavier particles in an area of chronic obstruction. In the stomach, the gravel sign often is easiest to see in a lateral view and typically in the pylorus. GDV can occur when the stomach rotates around its axis. It is more common in large, deep‐chested dogs, but can occur in any breed of dog and at any age. It is rare in cats but has been reported in a cat with a diaphragmatic hernia. Patients with GDV frequently present as an emergency, in a life‐threatening situation. Patients in severe distress must be stabilized prior to imaging. During gastric volvulus, the pylorus rotates from its normal position in the ventral, right side of the abdomen to the dorsal, left side (Figures 4.59 and 4.60). Volvulus also twists the esophagus at the cardia of the stomach. The duodenum follows the pylorus and moves dorsally and to the left, often wrapping around the esophagus. GDV results in an inability to eructate and an obstructed pyloric outflow. Figure 4.59 Gastric volvulus and dilatation (GDV). DV views of a dog cranial abdomen illustrating the stages of stomach rotation in a patient with GDV. A. The pylorus (P) moves to the left, pulling the duodenum (D) with it. B. As the pylorus and duodenum move to the left, the fundus moves to the right, pulling the spleen (S) with it. Rotation of the stomach causes a twist in the distal esophagus (E) at the cardia of the stomach. C. Continued rotation causes a more severe twisting at the distal esophagus, preventing eructation. The stomach dilates. The displaced spleen enlarges due to venous congestion. D. The pylorus ends up in the left cranial abdomen with the duodenum wrapped around the esophagus. The stomach is largely distended. The spleen is absent from its normal location in the left cranial abdomen. Figure 4.60 Gastric dilatation and volvulus (GDV). A. Cross‐sectional CT image of a dog abdomen depicting the normal appearance of the gastric fundus (F), the pylorus (P), the spleen (S), and the liver (L). The dashed white arrow indicates the movement of the pylorus during gastric volvulus. B. CT image depicting the same area in a dog with GDV. The pylorus is displaced dorsally and to the left and the fundus is displaced to the right. Both are dilated with mostly gas. The radiographic appearance of GDV is summarized in Table 4.2. Note: radiographic findings depend on the stomach contents, the degree of gastric distention, and the extent of rotation. The key to diagnosis of GDV is to locate the pylorus (Figures 4.60–4.63). Locating the pylorus is essential to differentiate GDV from gastric dilatation only. A displaced pylorus is easiest to identify when it contains gas. Because the pylorus typically rotates dorsally and to the left, the right lateral and DV views tend to be the most diagnostic. Remember, the dependent (down) parts of the stomach fill with fluid (and ingesta) while the non‐dependent (up) parts fill with gas. In right lateral and ventral recumbencies, a pylorus that is displaced to the left and dorsally will be “up” and more likely to fill with gas. Table 4.2 Radiographic findings with GDV The classic appearance of GDV in the right lateral view is commonly called compartmentalization of the stomach (Figures 4.60 and 4.61). Compartmentalization appears as a gas‐filled pylorus positioned craniodorsal to a gas‐and‐fluid‐filled fundus, and with a band of soft tissue opacity between them. Compartmentalization is considered by many to be pathognomonic for GDV but, like most radiographic signs, it is not 100% diagnostic. Figure 4.61 Gastric dilatation and volvulus (GDV). The classic appearance of GDV is depicted in these right lateral (A), left lateral (B), VD (C), and DV (D) views of a dog abdomen. The stomach is greatly distended with gas and fluid. In the right lateral view (A), the pylorus (P) is displaced dorsally and it is cranial to the fundus (F). There is a soft tissue opacity fold between them (white arrow). This finding is commonly called “compartmentalization of the stomach”, but it is not as evident in the other views. The spleen is displaced caudally and to the right (black arrows). It is mildly enlarged with rounded margins. The cardiac silhouette appears small (as seen at the periphery of the left lateral view, B) and the caudal esophagus is dilated with gas (yellow arrows). The pylorus is not readily identified in either the left lateral or the VD view because it is not filled with gas. In the DV view, gas is visible in the pylorus and duodenum (D), which aids in their identification. Figure 4.62 GDV with ingesta. Lateral view of a dog abdomen depicting a compartmentalized stomach that is greatly distended with gas and heterogeneous soft tissue opacity material. The gas‐filled pylorus (P) is craniodorsal to the food‐filled fundus. Figure 4.63 Gastric dilatation without volvulus. Three views of a dog abdomen depicting a stomach greatly distended with mostly gas but normal in orientation. A. In the right lateral view, fluid flows into the pylorus (white arrow) and duodenum (black arrow). The body and fundus of the stomach are largely distended with gas. B. In the left lateral view, gas rises to fill the pylorus (white arrow) and duodenum (black arrow), making them easier to identify. The body and fundus remain largely distended. C. In the VD view, gas rises to fill the pylorus (white arrows) and duodenum (black arrows), visible in their normal positions. Figure 4.64 Gastric foreign objects. A. Lateral view of a dog abdomen depicting mineral opacity foreign objects in the stomach. The ovoid objects in the body of the stomach (black arrow) are pieces of Pepto‐Bismol tablets. The object in the pylorus (white arrow) is an upside down rubber ducky toy (as shown in the inset photo B). Figure 4.65 Gastric foreign material. Lateral view (A) and VD view (B) of a cat abdomen. Multiple, curvilinear, mineral opacity objects are visible in the stomach and caudal esophagus (white arrows). These are ingested hair ties, examples of which are shown in the inset photo (C). Figure 4.66 Gastric foreign object. VD views of a dog abdomen depicting a round, soft tissue opacity object in the pyloric antrum (arrow). A. Survey radiograph: the object is not well seen because it is surrounded by fluid, which is the same opacity as the object. B. Negative contrast gastrogram: adding gas to the stomach provides an opacity interface to reveal the outline of the object. C. Postitive contrast gastrogram: adding barium to the stomach also provides an opacity interface to identify the object. Figure 4.67 Fluid in stomach. Lateral view (A) and VD view (B) of a dog abdomen depicting a stomach moderately distended with fluid and gas. The mucosal margin cannot be identified with certainty in these images. Fluid blending with the gastric mucosa may be mistaken for a thickened stomach wall (black arrows). Figure 4.68 Gastric rugae. Lateral view (A) and VD view (B) of a dog abdomen depicting a positive contrast gastrogram. The rugal folds create curvilinear filling defects (darker areas in the contrast medium); easier to see in the fundic region (black arrows). Figure 4.69 Thickened stomach wall. Lateral view (A) and VD view (B) of a dog abdomen depicting a positive contrast gastrogram. Most of the contrast medium has exited the stomach. A small volume fills the spaces between the rugal folds and outlines the mucosal margin. The gastric wall is thickened (white arrows), and the rugal folds are widened (black arrows). Figure 4.70 Filling defects. Two VD views of a dog abdomen depicting a gastrogram. The two radiographs were made a short time apart. In radiograph A, there are multiple filling defects along the outline of the stomach, some caused by peristalsis (white arrows) and others caused by gastric wall thickening (black arrows). In radiograph B, the indentations caused by peristalsis (white arrows) do not repeat, whereas those caused by wall thickening (black arrows) persist relatively unchanged. The thickened wall appears stiff and fixed in position. Figure 4.71 Gastric ulcers. Lateral view of a dog abdomen depicting a gastrogram with mucosal ulcers along the greater curvature (white arrows). The ulcers appear as focal, contrast‐filled outpouchings that persist in serial radiographs. Figure 4.72 Pyloric contraction. Two VD views of the same dog abdomen depicting a gastrogram. A. The pyloric canal is narrowed (white arrow) which may be due to normal peristalsis or pathology. B. In this second radiograph, made a short time later, the narrowing is not evident because it was caused by a peristaltic contraction. Figure 4.73 Stomach mural lesions. VD view of a dog abdomen depicting a gastrogram with multiple irregular‐shaped filling defects in the distal body and pyloric regions (black arrows). The lesions are visible along both the lesser and greater curvatures due to an annular neoplasm invading the stomach wall. Figure 4.74 Pyloric outflow obstruction. VD view of a dog abdomen depicting a gastrogram with marked narrowing of the pyloric canal (black arrow). Peristalsis pushing against the narrowing causes the stomach wall to bulge outward (white arrow) creating a pointed or “beak‐like” appearance near the pyloric canal. Figure 4.75 Normal small intestine. Lateral view (A) and VD view (B) of a dog abdomen depicting gas in the stomach, duodenum (D) and jejunum (J). The cranial duodenal flexure is part of the gastroduodenal angle (yellow arrow). Peyer’s patches are visible along the descending duodenum (white arrows), appearing as square‐shaped out‐pouches that extend away from the lumen. At the caudal duodenal flexure (black arrow), the duodenum curves to the left and then cranially. Figure 4.76 Normal distribution of the small intestine. A. Lateral view of a cat abdomen depicting even distribution of the small intestine (arrow). B. Lateral view of an overweight cat abdomen depicting crowding of the small intestine due to excess intra‐abdominal fat (arrows). C. VD view of the same cat as in B; the small bowel is confined to the right abdomen by the excess fat (arrow). Figure 4.77 Normal size of the small intestine. A. Lateral view of a dog abdomen depicting normal small intestine (arrow). The width of a bowel segment should not exceed twice the height of the body of the L5 lumbar vertebra (in cats, use the L3 or L4 vertebra). B. The height of the body of L5 is measured from its ventral border to the floor of the spinal canal (double headed arrow). C. The width of each bowel segment is measured from serosal margin to serosal margin (double headed arrows). Figure 4.78 Bowel wall thickness. A. Same lateral view as in Figure 4.77. The bowel wall thickness appears to differ between segments of small intestine (arrows). This is an artifact caused by fluid in the bowel lumen. B. Illustration depicting cross‐sectional and longitudinal views of a small bowel segment containing different volumes of fluid and gas. Fluid blends with the mucosal margin to create the appearance of a thickened bowel wall. (Special thanks to Dr. Tim O’Brien for the illustration.) Figure 4.79 Obstructive ileus. A. Lateral view of a dog abdomen depicting abnormally dilated small intestine. Bowel segments are both gas‐filled (black arrow) and fluid‐filled (white arrow). B. Lateral view depicting stacking or layering of both gas‐filled bowel segments (black arrow) and fluid‐filled segments (white arrow). The fluid‐filled bowel segments are less obvious. Figure 4.80 Horizontal beam radiograph. VD view of a dog abdomen made with the patient held erect and the x‐ray beam directed horizontally. Gas‐capped fluid levels are depicted in several abnormally distended segments of small intestine (white arrows). A normal gas:fluid level is depicted in the stomach (black arrow). Figure 4.81 Functional ileus. Lateral view of a dog abdomen depicting uniform dilation of the small intestine. The gas‐distended bowel segments are evenly distributed and similar in size. Figure 4.82 Intestinal ischemia. VD view of a dog abdomen depicting a dilated segment of small intestine with irregular margins that appear corrugated (white arrow). Figure 4.83 Intestinal pneumatosis. A. Lateral view of a cat abdomen depicting a functional ileus with gas in the small bowel wall (arrow). B. Cropped and enlarged part of radiograph A. Gas in the bowel wall (arrows) is due to mucosal damage caused by severe enteritis. due to severe enteritis and damage to the mucosa. Figure 4.84 Foreign objects in the small intestine. Lateral view of a dog abdomen depicting various ingested foreign objects, including a pacifier nipple (black arrow), diamond ring (yellow arrow), and a large piece of corn cob (white arrow). Figure 4.85 Fabric foreign material. A. Lateral view of a dog abdomen depicting dilation of the small intestine due to obstructive ileus (arrows). B. Cropped and enlarged section of the radiograph depicting the striated pattern of gas and soft tissue opacities that is characteristic of ingested cloth material (arrows). Figure 4.86 Fabric foreign material. A. VD view of a dog abdomen depicting the characteristic striated pattern of ingested cloth material in the descending duodenum (black arrow). The stomach is moderately distended with mostly gas. B. Cropped and enlarged section of the radiograph depicting a more detailed image of the striated pattern (arrows). In A, there is a gas‐filled, hyperperistaltic segment of small intestine in the left caudal abdomen (white arrow). Follow‐up radiographs would be helpful to differentiate normal peristalsis from pathology in this segment. Figure 4.87 Small bowel foreign material. Lateral view of a dog abdomen depicting a soft tissue opacity object in the descending duodenum (arrow points to a sock). It is unusual to see soft tissue opacity materials this well outlined by intestinal gas. Figure 4.88 Normal upper GI study. Lateral and VD views of a dog abdomen depicting the passage of barium through a normal GI tract. Radiographs A and B were made immediately after dosing (Time 0) and radiographs C and D were made 30 minutes later (Time 30), as indicated by the labels in each radiograph. Time 0: barium is visible in the stomach and duodenum. Pseudoulcers along the descending duodenum produce barium filled out pouches (arrows). Time 30: barium is visible throughout most of the jejunum and there is less barium in the stomach. Time 1 hour: the stomach is mostly empty of barium. The majority of the small bowel is opacified, but barium has not yet reached the colon. Time 2.5 hours: barium is visible in the colon. The stomach is virtually empty and a small amount of barium remains in the small intestine. Figure 4.89 Fimbria. Lateral view of a dog abdomen depicting a normal upper GI study. Intestinal villi project into the bowel lumen to create tiny, spiculated filling defects along the mucosal margin (black arrows). Figure 4.90 String of pearls. VD view of a cat abdomen depicting a normal upper GI study. The circular pattern of segmental peristalsis along the descending duodenum (arrows) is common in cats and known as the string of pearls sign. Figure 4.91 Corrugated bowel. Lateral view of a dog abdomen depicting an abnormal upper GI study. The mucosal border along a segment of jejunum is markedly irregular with numerous indentations that resemble “thumb imprints” (black arrows). This finding is typical of an annular, infiltrative disease (e.g., neoplasia, mycosis). Figure 4.92 Flocculation. Lateral view of a dog abdomen depicting a barium upper GI study. There is a mottled or speckled pattern in the jejunum (black arrow) caused by flocculation of the barium mixture. Figure 4.93 Complete vs. partial intestinal obstruction. A. VD view of a dog upper GI study depicting a complete blockage in the descending duodenum. The blockage prevents barium from passing into the more distal small intestine. The rounded proximal edge of the obstructing object is outlined by barium (may be a rubber ball, fruit pit, etc.). B. VD view of an upper GI study depicting an incomplete blockage in the proximal duodenum (black arrow). Some of the barium is able to pass into the jejunum (white arrow). The transit time, however, most likely is delayed. Figure 4.94 Linear foreign material. Lateral view of a cat abdomen depicting plication of the small intesine (arrow). The bowel is “scrunched” together, resembling a “scrunchie” hair tie (inset photo). Notice the tiny, crescent‐shaped gas bubbles in the plicated bowel. The bubbles do not resemble a normal intestinal gas pattern. Figure 4.95 Linear Foreign material. Lateral view (A) and VD view (B) of cat abdomen depicting an upper GI study. The descending duodenum is tortuous with multiple back‐and‐forth tight turns, i.e., plication (arrow). Figure 4.96 Linear foreign material. A. Survey radiograph VD view of a dog abdomen depicting an irregular intestinal gas pattern (arrows). B. Upper GI VD view of the same dog depicting tight, tortuous turns and bunching in the duodenum and jejunum (arrows). Figure 4.97 Linear foreign material. A. Survey lateral view of a dog abdomen depicting indistinct intestinal serosal margins and an atypical crescent‐shaped pocket of gas (arrow). B. Lateral view of the same dog during an upper GI study. The crescent gas pocket is again visible (white arrow) along with bunching of the small intestine. Some curvilinear material is present in the stomach (black arrow). The material is carpet fibers that are anchored in the stomach and extend into the small intestine. The carpet fibers were masked when the stomach was filled with barium, but are now visible because most of the barium has exited the stomach (some barium remains adhered to the fibers). Figure 4.98 Intussusception. Lateral view of a dog abdomen depicting a segment of jejunum (black arrow) sliding into the lumen of a distal jejunal segment (yellow arrow). The bowel walls are highlighted for illustration purposes. The proximal segment is distended with ingesta due to narrowing and obstruction at the intussusception. Figure 4.99 Normal canine large intestine. VD view of a dog abdomen depicting a barium enema. C = cecum (black arrow), I = ileum, A = ascending colon, T = transverse colon, D = descending colon, R = rectum. The yellow arrows point to the cecocolic and ileocolic junctions. Figure 4.100 Normal feline large intestine. VD view of a cat abdomen depicting a barium enema. C = cecum, I = ileum, A = ascending colon, T = transverse colon, D = descending colon, R = rectum. Figure 4.101 Redundant colon. Lateral view (A
4
Abdomen
Introduction to abdominal radiography
Procedure for making abdominal radiographs
Standard views of the abdomen
Supplemental views of the abdomen
Patient factors
Immature animals
Aged animals
Obese animals
Emaciated animals
Effects of positioning
Abdominal cavity
Normal radiographic anatomy
Abnormal size of the abdomen
Abnormal abdominal wall
Abdominal hernia or rupture
Abnormal opacity in the abdominal cavity
Gas in the abdominal cavity
Fluid in the abdominal cavity
Mineral opacity in the abdominal cavity
Intra‐abdominal mass
Liver
Normal radiographic anatomy
Liver in the lateral view
Liver in the VD/DV view
Abnormal liver position
Abnormal liver size
Small liver (microhepatia)
Large liver (hepatomegaly)
Liver mass
Abnormal liver opacity
Spleen
Normal radiographic anatomy
Spleen in a lateral view
Spleen in a VD/DV view
Abnormal spleen position
Abnormal spleen size and shape
Splenic torsion
Abnormal spleen opacity
Pancreas
Normal radiographic anatomy
Pancreatic disease
Gastrointestinal tract
Stomach
Normal radiographic anatomy
Gas and fluid in the stomach
Patient position
Fundus
Body
Pylorus
Right lateral
Gas
Gas
Fluid
Left lateral
Fluid
Fluid
Gas
Dorsal (VD view)
Fluid
Gas
Gas/Fluid
Ventral (DV view)
Gas
Fluid
Gas
Abnormal stomach position
Abnormal stomach size
Gastric dilatation and volvulus (GDV)
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