The Abdomen

CHAPTER two The Abdomen



THE ABDOMINAL CAVITY


The abdominal cavity is lined by the parietal peritoneum, which is continuous with the visceral peritoneum, which covers the viscera. The peritoneum is covered by a thin layer of fluid. The space between the parietal and the visceral peritoneum is normally a potential space. The mesenteries and the omenta are parts of the peritoneum. The retroperitoneal space is that area dorsal to the peritoneum and ventral to the sublumbar muscles. The kidneys lie in the retroperitoneal space.


Visualization of the abdominal organs depends on the following factors, taken singly or in combination:


1. Differences in opacity between one organ and another.

2. The amount of fat—retroperitoneal, mesenteric, and omental—present within the abdomen. Emaciated or very young animals with little abdominal fat show poor contrast.

3. The contents of the abdominal organs vary in density and consequently in opacity. Such contents may help outline the organs, such as air or gas in the stomach, or feces may outline the colon.

All the intraabdominal organs have a soft tissue or fluid opacity. One organ does not contrast well with another. Intraabdominal and perirenal fat provide some contrast. Apart from developmental anomalies, changes within the abdomen are caused by physiologic or pathologic processes. These processes are reflected as changes in opacity, size, shape, or position of intraabdominal structures. A normal structure may be displaced by an abnormal one or by a normal one that has increased in size as a result of physiologic changes. Functional disturbances can rarely be appreciated on plain radiographs. To demonstrate detail within the abdomen, special contrast procedures and ultrasonography are frequently necessary.



Radiography


The standard views used to study the abdomen are the left-right lateral recumbent, the right-left lateral recumbent, and the ventrodorsal. The dorsoventral view is not commonly used because when the patient is in sternal recumbency, the viscera are compressed and often irregularly displaced. A standing lateral view may sometimes be used, especially if an accumulation of peritoneal fluid is suspected. It should be remembered, however, that no fluid line will be seen unless there is a concomitant pneumoperitoneum (gas in the peritoneal cavity). Oblique views are useful in certain circumstances when it is necessary to examine the esophagus, stomach, colon, or bladder in more detail than is possible on standard views.


For lateral projections, the sternum should be supported by radiolucent foam pads to maintain it on the same horizontal level as the spine. The hindlimbs should be drawn caudally sufficiently far to prevent thigh muscles from overlying the caudal abdomen. The x-ray beam should be collimated to include the diaphragm and the pelvic inlet. On ventrodorsal views, on which the inguinal skinfolds may cast marked shadows, the “frog leg” position with the hind legs flexed may be preferred to having the hindlimbs drawn out caudally. Chemical restraint may be required with uncooperative animals where local radiation regulations preclude manual restraint.


Because the degree of contrast between the various abdominal organs is small, it is essential that good-quality radiographs be produced so that the maximum amount of information can be obtained. Adequate patient preparation and good radiographic technique are both important. Exposure factors using a lower kilovoltage increases the contrast within the radiograph.


In elective cases, the patient should be fasted for at least 12 hours before investigation. Water is allowed. The use of a mild cathartic administered the day before the examination is helpful. If the area of interest is the gastrointestinal tract, it is probably best not to give an enema initially because it may cause significant changes in the radiologic picture. An enema may be given after the initial survey studies have been made. Isotonic saline enemas are recommended. The temperature of the enema fluid should be lower than body temperature. This lower temperature helps cause expulsion of much of the gas that would remain in the colon if a warm enema were given.



Evaluation of the Abdominal Radiograph



1. A good abdominal radiograph should show the structures in the cranial and caudal abdomen and the abdominal wall.

2. There should be good range of contrast so that the various abdominal structures can be clearly distinguished from one another.

3. Falciform and retroperitoneal fat should be identifiable.

4. The bodies of the vertebrae should be clearly outlined and the bone density clearly identifiable.

5. The film should be neither overexposed nor underexposed.

To determine the thickness of the abdomen when a technique chart is used, the measurement should be made at the point of greatest depth, usually over the caudal rib cage. The actual exposure should be made during the expiratory pause. A grid should be used for animals when the abdomen has a thickness of 10 cm or more. In deep-chested animals on the ventrodorsal view, visualization of the abdominal organs is often poor because of the wide variation between the area of the caudal rib cage and the area of the pelvic inlet.



Normal Appearance


On survey radiographs of the abdomen, the diaphragm, abdominal wall, stomach, small intestine, large intestine, liver, and bladder can usually be recognized. On the ventrodorsal and left-right lateral recumbent views, the spleen is also usually seen. The kidneys may or may not be seen depending on the amount of perirenal fat present. The left kidney is seen in most dogs, whereas only the caudal pole of the right may be visible. The complete outline of both kidneys is usually visible in cats. The os penis is seen in the male dog. The prepuce of the male dog is usually seen because of the air that surrounds it, and the teats are often seen in the female for the same reason. The prostate gland may be seen if there is sufficient intrapelvic fat to outline it. The position and appearance of the normal viscera vary somewhat with the posture of the animal, its conformation, respiratory movements, and the amount of food material present in the alimentary tract (Figure 2-1).


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Figure 2-1 A and B, Ventrodorsal views of a normal abdomen. C and D, Lateral views of a normal abdomen (B and D: 1, Stomach; 2, liver; 3, spleen; 4, kidneys; 5, bladder; 6, colon; 7, cecum; 8, small intestine).E, Normal puppy abdomen. Contrast is poor in this 3-month-old puppy. F, Normal teat shadows. G and H, Normal male dog abdomen. G, Right lateral and H, ventrodorsal radiographs of a normal abdomen of a male dog. A moderate amount of food is present in the stomach, which indicates the caudal margin of the liver. The cecum is a C-shaped gas-filled segment of bowel seen in the midabdomen on the lateral radiograph and in the right midabdomen on the ventrodorsal radiograph. In G, the left kidney is outlined by fat. The right kidney is not seen because it is obscured by superimposition of the colon. The tail of the spleen appears as a thin, elongated, fusiform soft tissue structure in the ventral midabdomen.I to L, A series of CT images demonstrating the normal anatomic relations of the abdominal structures. The right side of the abdomen is on the left side of the image. I, A transverse CT image of the cranial abdomen of a normal dog is displayed in a soft tissue window. The liver has relatively uniform attenuation, but the gallbladder and contents are hypoattenuating compared with the liver. The hepatic veins are slightly hypoattenuating compared with the liver tissue. Note also the falciform fat (arrow) ventral to the liver and gallbladder (asterisk). A small volume of fluid is present in the caudal thoracic esophagus just ventral to the vertebral body, and an air-fluid interface is seen. This is not an uncommon finding. The patient was scanned in dorsal recumbency. J, A transverse CT image of the abdomen of a normal dog at the level of the left renal pelvis. The kidney tissue has uniform attenuation. Fat is seen at the renal hilus (arrows) surrounding the renal pelvis and renal vessels. Part of the spleen is visible ventral and to the left of the left kidney. There is a defect in the left side of the vertebra, a result of previous spinal surgery. K, A transverse CT image of the abdomen at the level of the splenic hilus. The cranial pole of the right kidney (asterisk) is seen partially surrounded by the renal fossa of the caudate lobe of the liver (arrows). The head of the spleen is folded medially in the left abdomen. L, A transverse CT image of the abdomen of a normal dog at the level of the iliac wings. The colon contains mixed attenuation material and multiple small gas bubbles in the center of the image. It lies dorsal to the urinary bladder and indents the dorsal border of the bladder. The urine within the bladder (UB) is slightly hypoattenuating compared with the urinary bladder wall. Note also the external iliac arteries and veins (arrows) dorsal and lateral to the colon and ventral to the iliopsoas muscles.M, Normal female dog abdomen. Right lateral abdominal radiograph. The tail of the spleen (arrows) lies in the ventral central abdomen. Fat is interposed between the stomach and liver. N and O, Normal thin dog. Abdominal contrast and serosal detail are reduced in this dog because of the absence of fat. Fat provides contrast within the abdomen. The liver and spleen are not clearly visible. R, Right side.



Ultrasonography


Abdominal ultrasound is usually performed as a complementary technique to radiography. The combination of both imaging modalities results in more information as to size, shape, and position of organs. In addition, ultrasound provides accurate information on the outline and architecture of tissues.


Ultrasonography can be performed anywhere on the abdominal wall, the only impediment being bone and gas-filled structures, which should be avoided. If a general examination is to be performed, then a systematic approach is required. Unless a high-frequency transducer is used, the abdominal wall will not be clearly discernible.


Chemical restraint is rarely required except when severe abdominal pain is present. Lateral or dorsal recumbency are options, but dorsal recumbency is the usual position. Left lateral recumbent positioning avoids gas rising into the fundus of the stomach. When using lateral recumbency, the patient must be turned to allow the entire abdomen to be examined. Lateral examination from the dependent side, using a cutout table or platform, is used for some examinations because imaging from the dependent side helps avoid gastrointestinal gas. Large dogs may be examined with the animal in the standing position. The hair is clipped close, and an acoustic coupling gel is applied to the skin. Cleaning the skin with alcohol is advocated to improve image quality. However, the use of alcohol on recently clipped skin may cause discomfort. Abdominal ultrasonography may be required to examine a specific organ or for a general examination. The area of skin preparation will vary depending on the purpose of the study.


For small to medium dogs, a 5- to 10-MHz transducer will be adequate. Large and giant breeds will require a 3.5- to 5-MHz transducer. Examination of structures in the cranial abdomen may require an intercostal approach, and a small transducer footprint will be necessary to avoid the ribs.


The usual planes of section are transverse, a cross-section through the body, and a sagittal section or longitudinal section parallel to the vertebral column. Because many organs are somewhat mobile, orientation planes will relate to the organ under examination. Organs such as the kidney often need a third plane of section termed dorsal. This plane requires the transducer orientated in a craniocaudal direction but aligned along the right or left wall of the abdomen. The convention is to display the cranial aspect of the animal on the left side of the image.



Abnormalities



Abdominal Masses


Masses within the abdominal cavity are from enlargements of one or more of the intraabdominal structures. Enlargement of an organ may be attributable to physiologic or pathologic processes. Distention of the stomach after eating, enlargement of the uterus during pregnancy, and enlargement of the spleen during barbiturate anesthesia are examples of physiologic enlargements. Pathologic enlargement may be the result of inflammatory processes; abscess or cyst formation; hematoma, torsion, obstruction; or neoplasia. Hypertrophy may cause enlargement of an organ.


A mass can usually be identified on a plain radiograph. Abdominal masses are sometimes masked by intraabdominal fluid. If there is accompanying fluid, it should be removed and another radiograph made so that the mass may be more accurately identified. Alternatively, ultrasonography may be used. Some estimation of the origin of a mass may be gained from its position and from the manner and degree of displacement of other organs. Organs amenable to displacement are the stomach, the small and large intestines, the spleen, the uterus, the bladder, and to a lesser extent the kidneys. Movable organs will be displaced in a direction away from the mass. Such displacements often permit the examiner to suggest which structure is enlarged. For example, an enlarged liver displaces the stomach caudally and dorsally.


Sublumbar masses can be seen on lateral views. They may be caused by enlarged medial iliac (sublumbar) lymph nodes, enlarged renal silhouettes, ureteral rupture with accumulation of urine, hemorrhage, abscess formation, adrenomegaly, infection, or neoplasia of vertebrae or sublumbar structures. They displace the adjacent abdominal organs ventrally. Enlarged lymph nodes may present as intraabdominal masses in other locations (Figure 2-2, A to E).


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Figure 2-2 A and B, An 11-year-old Collie crossbred dog with abdominal swelling. The intestines are displaced dorsally, caudally, and laterally by a mass involving the midbody of the spleen. C, A large mass arising in the spleen. D, Masses (arrows) associated with enlarged sublumbar lymph nodes. E, Abdominal mass. This 12-year-old crossbred dog presented with a swollen abdomen. The tentative clinical diagnosis was ascites. The abdominal organs are displaced cranially and dorsally by a large mass. The mass has a fat opacity. The mass was a lipoma.F, This 15-year-old Terrier presented with lethargy and depression. A well-marginated mass lies within the body of the spleen (arrows). Focal anechoic areas (a) with septa are seen. Hypoechoic neoplastic tissue (h) lies caudally. Diagnosis: hemangiosarcoma. G, A close-up image of an enlarged lymph node (arrowheads) located medial to the spleen (arrow). It is rounded and plump. Several others were found within the abdomen. Diagnosis: lymphosarcoma.



Ultrasonography


Ultrasonography is useful in confirming the clinical or radiologic diagnosis of an abdominal mass. It also permits identification and localization of the organ of origin and assists in evaluation of other organs for concomitant disease. It should be done before abdominocentesis. Ultrasound-guided fine-needle aspiration or biopsy aids in a definitive diagnosis of such masses (Figure 2-2, F and G).



Intraperitoneal Fluid


Intraperitoneal fluid may be exudative or transudative in origin, or it may be blood, chyle, urine, or bile. Ascites is defined as an effusion and accumulation of serous fluid in the peritoneal cavity. Common causes of ascites are congestive heart failure, liver abnormalities, renal disease, hypoproteinemia, peritonitis, and abdominal neoplasia. The term ascites is used colloquially to describe the presence of any fluid in the abdominal cavity.



Radiologic Signs



1. The abdomen appears more radiopaque than normal. Its overall hazy appearance makes the radiograph appear as if it were underexposed. Clear visualization of the vertebral column indicates the exposure to be adequate.

2. The increased opacity is widely distributed throughout the abdomen, causing loss of the detail normally seen. Serosal surfaces are obscured to some degree depending on the amount of fluid and fat present.

3. Gas within the bowel may be seen through the fluid, but details of the serosal surfaces are lost.

4. There is an increased distance between individual loops of intestine that are separated by the fluid.

5. With large volumes of fluid, the intestines tend to occupy a central position in the abdomen unless displaced by an abdominal mass.

6. The abdomen is distended because of the fluid within it.

7. Standing lateral films show an increased opacity in the ventral abdomen where the fluid accumulates and a more natural appearance dorsally. Loops of intestine that contain gas tend to rise to the dorsal abdomen and “float” on the fluid. A gas-fluid interface (fluid level) will not be seen unless there is free gas within the peritoneal cavity (pneumoperitoneum). Fluid levels may be seen within the intestinal tract.

8. Occasionally the faint outline of an intraabdominal mass is identified through the fluid.

9. Smaller amounts of fluid may give the abdomen a hazy or mottled appearance (Figure 2-3, A and B).

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Figure 2-3 A and B, Ascites in a cat. The abdomen is grossly distended, and there is loss of intraabdominal detail. There is rotation of the abdomen on both views. The distention made accurate positioning difficult. C, This neutered male 15-year-old cat has a grossly distended bladder. The cranial and dorsal displacement of the intestines distinguishes it from ascites. D, Intraabdominal fluid (F) surrounds an enlarged liver (L) with rounded, nodular margins (M and arrows). Cr, cranial. E, This German Shepherd presented depressed and with palpable abdominal fluid. The abdominal sonogram was obtained with the dog in the standing position. It shows the free fluid (F) to be highly echogenic because of a high cellular content. The colon (C) lies to the left. Diagnosis: splenic adenocarcinoma. F, This dog was examined in dorsal recumbency. Intraabdominal fluid (F) outlines the kidney (K) lying in the retroperitoneal space. Cr, cranial.


Other conditions may give a somewhat similar appearance to that of ascites. Intraabdominal hemorrhage may be caused by trauma or anticoagulant poisoning. Effusion of fluid may be associated with peritonitis with loss of detail within the abdomen, either localized or generalized, but the abdomen is not distended. Metastatic seeding of neoplasms may cause loss of intraabdominal detail and be associated with effusion. Emaciation causes loss of intraabdominal detail because of fat depletion. Young animals lack intraabdominal fat and thus show poor intraabdominal detail. Care should be taken not to mistake a fluid-filled viscus for ascites. A grossly distended bladder can extend very far cranially into the abdomen. Perinephrotic pseudocysts may be quite extensive and simulate ascites. An enlarged viscus will displace adjacent organs (Figure 2-3, C). Small amounts of fluid can be difficult to demonstrate radiographically.



Ultrasonography


The presence of intraabdominal fluid, which is a hindrance in radiologic evaluation of the abdominal cavity, assists ultrasonographic examination. Ultrasonography is more sensitive than radiography in detecting small volumes of free fluid. Transudates tend to be anechoic. Anechoic fluid dissecting between organs permits their margins to be examined because the fluid profiles organ edges. Fluid surrounding the bladder or gallbladder throws their walls into relief so that their internal and external aspects can be identified. Abdominal organs appear more echogenic than usual when surrounded by intraabdominal fluid. The relative echogenicity of the fluid can be compared with the normal anechoic urine or bile. Free blood in the abdomen has a more echogenic specular texture than a transudate or modified transudate. Peritoneal masses are also seen, provided they are profiled by fluid. Gross abdominal distention resulting from fluid can make examination difficult because the animal may resent transducer pressure. Abdominocentesis relieves the pressure and makes the procedure less stressful, but care must be taken not to introduce air into the abdomen (Figure 2-3, D to F).



Peritonitis


Peritonitis is inflammation of the peritoneum. It may result from infection, rupture of an abdominal organ, trauma, or a penetrating wound of the abdominal wall. It may be secondary to pancreatitis or pancreatic neoplasia. Peritonitis causes loss of the sharp outline of the abdominal organs so that the abdomen in the affected area appears hazy or blurred. Serosal surfaces are not clearly seen. An associated outpouring of fluid enhances the effect. Large amounts of fluid produce a homogeneous opacity. Small irregular areas of increased opacity (mottling) are often evident as a result of an irregular distribution of small amounts of fluid. There may be associated adhesions.


Peritonitis may be localized or generalized. If it is localized, only those structures in the affected area will lose their radiographic sharpness. If it is generalized, there is a widespread haziness of the abdomen. Abdominal carcinomatosis or metastatic neoplasia produces a picture similar to peritonitis. A nodular or granular pattern may be seen (Figure 2-4, A to G).


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Figure 2-4 A, Loss of intraabdominal detail in the midabdomen as a result of peritonitis. A 6-year-old Labrador presented with severe vomiting and abdominal pain. There is poor serosal detail and indistinct organ margins. The abdomen has a granular appearance distinct from the homogeneous appearance of ascites. B, A 10-year-old Labrador presented off form, dull, and with abdominal swelling. On the lateral radiograph there is an ill-defined soft tissue opacity in the caudal ventral abdomen. Serosal detail is poor. A vaguely granular texture is evident in the ventral abdomen. At necropsy, a mass was found involving the mesenteric fat with mesenteric seeding scattered throughout the abdomen. The mass was a liposarcoma. C, A 10-year-old German Shepherd presented in a state of shock and dehydration. There is a focal lack of serosal detail in the midventral abdomen. There are patchy striations in the area. The metallic opacities are foreign bodies. This was a focal peritonitis after perforation of the bowel wall.D and E, An 11-month-old female German Shepherd had an ovariohysterectomy 4 weeks previously. It was anorexic and pyretic. D, This lateral view shows a soft tissue mass with a foamy radiolucent center displacing the small intestine ventrally and the large intestine craniodorsally. E, On the ventrodorsal view the mass is seen to lie to the right of L5-L7 (arrow). This was a surgical sponge/swab in an intraabdominal abscess. F, This is a close-up view of the midventral abdomen of a dog. There is poor serosal detail because of peritonitis. In the center of the image a foamy radiolucent structure is visible displacing the small intestine dorsally. This was a surgical swab or sponge.G and H, Peritonitis. A 6 1/2-year-old Border Collie had pyrexia of unknown origin. G, A lateral abdominal radiograph shows poor serosal detail in the midabdomen caudal to the stomach. The small intestine is displaced ventrally and caudally. H, An ultrasonogram shows a 6-cm encapsulated hypoechoic mass (H) caudal to the stomach and medial to the duodenum (D). At surgery this mass was found to have been caused by necrotizing pancreatitis. I, This dog presented with abdominal pain and vomiting. Radiography suggested peritonitis. A midline sagittal sonogram shows hyperechoic mesenteric fat (M). This was peritoneal inflammation as a result of severe pancreatitis. I, intestine. J, Peritonitis. This dog had surgery 4 days earlier for removal of an intestinal foreign body. Abdominal pain and depression were noted, and an abdominal sonogram was requested. Ventrally, echogenic fluid (P) was seen surrounding hyperechoic mesenteric fat (M). A laparotomy confirmed intestinal dehiscence, ileus, and purulent peritoneal fluid. Cr, Cranial; I, intestine.


In cats, steatitis may cause peritonitis with loss of detail in areas with accumulations of fat—the falciform ligament, the perirenal areas, and the inguinal and sublumbar regions.



Ultrasonography


The presence of echogenic particles oscillating in the abdominal fluid with or without strands of hyperechoic tags of fibrin is suggestive of peritonitis. The serosal surfaces of the abdominal organs may show an irregular outline. All abdominal organs should be carefully examined for a potential source of regional peritonitis (Figure 2-4, H to J).



Free Gas in the Abdomen


Free gas (air) may be seen in the abdomen for up to 4 weeks after laparotomy. Intraabdominal gas may also be the result of a penetrating wound through the abdominal wall or rupture of a viscus.



Radiologic Signs



1. The gas usually has an irregular distribution and does not conform to the shape of normal gastrointestinal gas.

2. Small bubbles trapped between bowel segments may be seen as arrow-like shapes or as triangles.

3. The position of free gas changes according to changes in posture of the animal. A small amount of gas may easily be missed, especially if it is superimposed on part of the intestinal tract.

4. Free gas may outline the liver and be seen between the diaphragm and the liver. It may outline the stomach and the ventral border of the kidneys.

5. Free gas in the abdomen may be demonstrated on a ventrodorsal view with the animal placed in left lateral recumbency and using a horizontal beam (decubitus position). This is the study of choice, because on decubitus ventrodorsal views made in right lateral recumbency, there may be difficulty in distinguishing free gas from gas within the gastric fundus or colon. Several minutes should be allowed to elapse from when the animal is positioned until the radiograph is made. This interval will allow the gas to reach the highest point within the abdomen. The gas will be seen in the uppermost part of the abdomen under the caudal ribs.

6. Free gas may also be demonstrated on a standing lateral view when it will be seen to collect in the sublumbar area.

7. If gas is present in considerable amounts, the various abdominal organs will be outlined by it, and the film may appear to be overexposed (Figure 2-5).

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Figure 2-5 Free air within the abdomen after a laparotomy. A, A left lateral recumbent view with a horizontal beam shows air (arrows) under the ribs. B, The animal was supported by the forelegs in a vertical position (erect), and a horizontal beam was used to obtain a ventrodorsal view. Air can be seen caudal to the diaphragm (arrows). C, The kidneys are outlined by pneumoperitoneum with a horizontal beam.D, A lateral abdominal radiograph with a horizontal beam, with the patient in dorsal recumbency. There is gas within the pyloric antrum and body of the stomach (asterisk). Two horizontal lines, representing gas fluid interfaces (arrows), are present within the stomach. No gas is present within the peritoneal cavity. With the patient in this position, free peritoneal gas will rise and accumulate just caudal to the xiphoid and ventral to the liver. E, Free intraperitoneal gas in a dog. This is a lateral radiograph obtained with a horizontal beam and the patient in dorsal recumbency. Free gas rises to the cranioventral aspect of the abdomen. Gas outlines the caudal surface of the diaphragm (long arrows) and ventral border of the liver and stomach (arrowheads). A large pocket of gas (asterisk) is visible within the pyloric antrum and body of the stomach. This should not be confused with free peritoneal air. Because the patient is in dorsal recumbency, the heart is displaced slightly from the sternum, which should not be mistaken for a pneumothorax. The horizontal line that crosses the image is the edge of the foam positioning device. F, This is a midline abdominal sonogram of a dog with pneumoperitoneum after a laparotomy. Gas within the small intestine is causing reverberation artifacts (long arrow). Free intraabdominal air (short arrow) is seen lying immediately adjacent to the abdominal wall (arrowhead) and also generating reverberation artifacts.



Ultrasonography


Ultrasound may be more sensitive for detecting small volumes of free gas. The patient should be placed in lateral or dorsal recumbency and a few minutes allowed to elapse before scanning to allow bubbles to rise to the upper abdominal wall. A high-frequency linear probe is recommended. Free gas appears as a hyperechoic structure with comet-tail artifacts immediately adjacent to the inner margin of the abdominal wall. Free gas has a similar sonographic appearance to intestinal gas but is distinguished by the absence of a surrounding bowel wall (Figure 2-5, F).



THE ABDOMINAL WALL


Cranially the abdomen is bounded by the diaphragm. Laterally and ventrally it is bounded by the ribs and the abdominal musculature. Its dorsal boundary is formed by the sublumbar muscles. It is lined by the peritoneum, which forms the caudal limit of the abdomen. With the exception of the peritoneum all these structures can be identified on plain radiographs.



Abnormalities


A disruption in the continuity of the diaphragm or the abdominal musculature results in a rupture. There may be mineralization within the muscles in Cushing’s disease (see Figure 6-1, F). Gas may track along fascial planes in pneumomediastinum or after trauma. Tumors of the abdominal wall are rare and the outline may be obscured by intraabdominal fluid.



Hernias


A distinction may be made between protrusions that have a peritoneal lining and those that have an associated abdominal wall rupture. A hernia is a protrusion of abdominal organs through a natural or physiologic opening so that they come to lie beneath the skin. The peritoneum remains intact. A rupture is a protrusion of abdominal organs through a breach in continuity of the abdominal wall. The terms are often incorrectly used interchangeably.


Radiography is sometimes of value in the diagnosis of a hernia. If a hernia becomes strangulated or incarcerated, dilated loops of bowel are seen proximal to the herniated portion of intestine, and the herniated intestine may be dilated.


Ultrasonography can be used to identify the contents of a hernia. Fat will be identified as relatively hyperechoic material within the sac. Intestinal loops may be seen as linear structures containing hyperechoic gas, anechoic fluid, or a mixture of both. Peristalsis may be appreciated if present. If the bladder is herniated and if it contains urine, it is easily identified because the anechoic urine readily confirms the diagnosis. Figure 2-6 shows examples of hernias and ruptures.


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Figure 2-6 A and B, Diaphragmatic rupture (hernia). Small intestine gas shadows can be seen within the thorax (arrows). The abdomen appears empty except for the large intestine. The diaphragm lines are obscured. C, A large inguinal hernia. Small intestine gas shadows are seen within the hernial swelling on this lateral view.D, A perineal hernia containing the bladder. The bladder is outlined by positive contrast medium (arrows). E, Peritoneopericardial hernia. The cardiac shadow is enlarged and distorted. Small and large intestinal gas shadows can be seen within the cardiac outline (see Chapter 3, p. 257). F, A 4-year-old Labrador had surgery for a long-standing diaphragmatic hernia some 4 weeks before presentation. A portion of stomach can be seen in the caudodorsal thorax. This proved to be a hiatal hernia. G, Inguinal hernia. A 5-year-old female domestic short-haired cat had been off form for several months. The left kidney is grossly enlarged. The bladder lies ventral to the abdominal floor in an inguinal hernia and is seen just cranial to the femurs. Ultrasonography showed the left kidney to be hydronephrotic. The cause was obstruction of the ureter caused by the abnormal bladder location.H, Paracostal hernia. A 10-year-old crossbred Terrier was lame and had a subcutaneous swelling over the ribs. The ventrodorsal radiograph shows a large soft tissue mass with a gas shadow cranially in the left paracostal region. The adjacent ribs are spread by the mass. This was a herniated stomach. I, Inguinal abscess. This 7-year-old Cocker Spaniel had an inguinal hernia repair 4 days before presentation. There was vomiting, polydipsia, and polyuria. The hernial mass was fluctuant. A lateral radiograph shows a soft tissue swelling lying ventral to the abdominal wall and containing gas and fat opacities. J, This 12-year-old Pointer has a large fluid-filled structure within an inguinal mass (arrowheads). A large, predominantly anechoic, fluid-filled mass lies within the inguinal area. The lumen contains some echogenic material. Several stellate hypoechoic fibrin strands or septa are scattered throughout the mass. Diagnosis: postoperative seroma. K, A fluid-filled loop of intestine (i) is seen in cross-section within a small inguinal hernia. L, This dog was involved in a road traffic accident 2 weeks earlier. On clinical examination there was a nonreducible mass in the inguinal region. A gas-filled loop of intestine (arrow) lies within an inguinal hernia. An acoustic shadow is seen distally (short arrows).M, Hiatal hernia. A 9-month-old Wolfhound puppy had a history of acute vomiting for 4 weeks. A lateral radiograph shows the food-filled fundus of the stomach herniated through the esophageal hiatus and lying in the caudodorsal thorax. There is air in the esophagus dorsal to the trachea. N, Retroperitoneal hemorrhage. This Greyhound had a history of poor performance and recurrent abdominal distention after work. The lateral radiograph shows a retroperitoneal soft tissue opacity displacing the abdominal organs ventrally. O and P, Sagittal (O) and transverse (P) images of the caudal abdomen at the level of the terminal aorta. O, Rounded, plump medial iliac lymph nodes (arrowheads) lie adjacent to the terminal aorta (asterisk). P, The transverse image shows an enlarged lymph node (asterisk) lying laterally to the caudal vena cava (arrowhead) and aorta (arrow). This was a lymphosarcoma.



Inguinal Hernia


Radiography can be helpful in determining the contents of an inguinal hernia. Gas shadows within the hernial outline indicate the presence of a portion of intestine. The uterus casts a homogeneous, fluid type of opacity, as does the bladder. Fetal skeletons may be seen if the animal is in late pregnancy. A barium study can be used to determine the position of the intestine. Ultrasonography will determine the contents (Figure 2-6, C, G, K, and L).



Ventral Hernia


There may occasionally be doubt as to the nature of a swelling on the abdominal wall. In the case of a ventral hernia, radiographs may show loops of intestine containing gas outside the abdomen and under the skin. The point of herniation may be seen as a discontinuity in the shadow of the abdominal wall. If necessary, intraperitoneal or subcutaneous injection of water-soluble contrast material will coat the abdominal contents and show their position.


Fat and intestines may be identified on ultrasonography. Close examination of the abdominal wall may identify the site of herniation.



Perineal Hernia


Radiographs can be helpful in determining the contents of a perineal hernia. Contrast cystography (see p. 148) will show whether the bladder is in the hernia. If there is retroflexion of the bladder, introducing contrast medium may be difficult.


Fat, a displaced rectum, or the anechoic urine-filled bladder may be identified in the perineal swelling on ultrasound examination (Figure 2-6, D).



Hiatal Hernia


In this hernia there is a protrusion of the stomach, or part of it, through the esophageal hiatus of the diaphragm, displacing the terminal esophagus cranially. The cardiac area of the stomach is most likely to be involved. The term hiatal hernia implies a herniation of part of the stomach through the esophageal hiatus into the thorax. With the sliding type of hernia, the displacement is intermittent and usually affects the gastroesophageal junction, together with the cardia of the stomach. A barium study will show the position of the stomach. These hernias are common in brachycephalic dogs. To demonstrate this hernia, it may be necessary to have the animal tilted with the head down because the stomach may slide into and out of the thorax. Fluoroscopy, while feeding the animal barium mixed with food, may show a sliding hernia.


In a paraesophageal hernia a portion of the stomach passes through the esophageal hiatus to lie alongside the esophagus. This type usually does not affect the gastroesophageal junction and is rare in dogs and cats. Clinical signs are primarily dysphagia, regurgitation, and discomfort after eating (Figure 2-6, F and M). Gastroesophageal intussusception is a rare form of hiatal hernia in which all or part of the stomach invaginates into the esophagus (see p. 75). The hernia appears as an elongated fusiform soft tissue mass in the dorsal thorax, displacing the trachea ventrally and distorting the heart. The absence of a normal stomach shadow in the abdomen is an important radiographic clue.



Diaphragmatic Hernia


Diaphragmatic hernia (rupture) is described in Chapter 3. Celiography or peritoneography, that is, introduction of contrast medium into the peritoneal cavity, has been described as an aid in the diagnosis of these hernias. Abdominal organs may be seen within the pericardium in peritoneal pericardial hernia (see Chapter 3, p. 257; and Figure 2-6, E).



Umbilical and Scrotal Hernias


Umbilical and scrotal hernias are usually diagnosed on a clinical examination. Displaced loops of intestine may be seen on radiographs that include the area of the hernial sac. Ultrasonography will identify the contents of the hernia (see Figure 2-56, N).



Abscess


On radiographs an abscess presents as an intraabdominal mass. It may be homogeneous in nature or contain focal lucencies. There may be local lack of serosal detail because of peritonitis. Regional ileus and bunching of the intestines may be observed. Abscess formation may be caused by perforation of the gastrointestinal tract, pancreatitis, foreign body such as a surgical swab or sponge, or trauma (see Figure 2-4, D to F, and Figure 2-6, I).



Ultrasonography


On ultrasonography, intraabdominal abscesses, or abscesses within hernias, produce hypoechoic, poorly marginated masses containing variable quantities of fluid. They usually have a mixed echogenic appearance and are surrounded by a capsule and may be attached to the serosal surface of abdominal organs or to the abdominal wall. Adjacent inflammation may be indicated by hyperechoic fat, pockets of anechoic/hypoechoic fluid, and regional intestinal ileus (see Figure 2-4, H). The presence of echogenic particles oscillating in the abdominal fluid with or without strands of hyperechoic tags of fibrin is suggestive of peritonitis. Serosal surfaces of adjacent organs may show an irregular outline (see Figure 2-4, I and J).



THE RETROPERITONEAL SPACE


The retroperitoneal space is the area that lies between the sublumbar muscles and the peritoneum. It contains the medial iliac (sublumbar) lymph nodes, the kidneys, the prostate gland, the adrenal glands, the aorta, and the caudal vena cava. Part of each ureter lies within it. It normally contains an amount of fat, which provides contrast. The kidneys and the prostate protrude from the retroperitoneal space into the abdomen and thus are partially covered by peritoneum.



Abnormalities


The retroperitoneal space may be the seat of sublumbar masses caused by abscessation; enlarged lymph nodes, kidneys, or adrenal glands; or neoplasia of sublumbar muscles, connective tissue, or vertebrae. Retroperitoneal fluid may be caused by hemorrhage or leakage of urine from the kidneys or ureters (Figure 2-6, N). Gas or air from a pneumomediastinum is occasionally seen outlining structures in this region.



Ultrasonography


Ultrasonographic examination permits examination of the sublumbar region. Lymph nodes, vessels, and kidneys are clearly visible. Masses in the region are readily accessible for fine-needle aspiration or biopsy provided that major blood vessels are avoided (Figure 2-6, O and P).



Abdominal Blood Vessels


Every sonographic examination of the abdomen should include an examination of the intraabdominal blood vessels. Congenital anomalies, with or without related organ changes, neoplasia, infiltration, or thrombosis, are among the conditions that may be encountered. In the evaluation of vessels, familiarity with their anatomic features is essential. High-frequency transducers are usually used, though larger animals may require lower frequencies. The animal should be fasted for 8 to 12 hours before examination. The method of choice is imaging through the paralumbar region in the dorsal and transverse planes. Studies are more easily performed with the animal in right and left lateral recumbency as the transducer is placed dorsally in the sublumbar fossa and gastrointestinal gas is avoided.


From the left side, the aorta is seen in the near field, that is, nearest to the transducer. The vena cava is seen on the far side of the aorta (far field). The aorta is identified by its pulsation, which may affect the adjacent vena cava.


As one moves from the cranial to the caudal abdomen, the major branches of the aorta can be identified, namely, the celiac, the cranial mesenteric, paired phrenico-abdominals, paired renal, testicular or ovarian, paired lumbar, caudal mesenteric, paired deep circumflex iliac, and external iliac arteries.


Similarly, the main branches of the vena cava are the common iliac veins, paired deep circumflex iliac, right testicular or ovarian, paired renal and phrenicoabdominals, and multiple hepatic veins.


The portal vein is located in the midventral abdomen and is the vessel closest to the transducer when imaging from the right side with the animal in left lateral recumbency (Figure 2-7, H and I).


image image

Figure 2-7 A, Positions of the normal liver and spleen. B, A ventrodorsal view of the abdomen with the outline of the head of the spleen (arrows). C, Midline sagittal sonogram of the cranial abdomen. The relative echotextures of the liver (L) and spleen (S) can be seen. The spleen is hyperechoic compared with the liver. The structure in the far right field is the fluid-filled stomach. D, Normal sharp edge to the caudal liver margin (arrows). E, Midline sagittal sonogram of the liver (L) of a fat dog showing a large quantity of fat (F) in the ventral abdomen outlining the liver margin (arrows).F1, Normal portal vessels (arrows) in the liver. The portal vessels have bright hyperechoic walls. F2, This midline sonogram of the liver shows normal portal vessels (short arrow) and hepatic veins (long arrow). G, Hepatic veins (arrowheads) draining into the caudal vena cava (CVC). GB, gallbladder. H, Color flow Doppler sonogram showing the caudal vena cava (long arrow coded blue) traveling toward the diaphragm. The aorta is seen in the far field (short arrow, coded red) (see Color Plate 2-7, H). I, This sagittal plane sonogram shows the terminal aorta bifurcation (long arrow) and caudal vena cava (medium arrow) bifurcation and the external iliac vessels (small arrows). J, Bones in the stomach of this 11-year-old Labrador were an incidental finding and were fully digested 24 hours later.



THE LIVER



Anatomy


The liver lies within the intrathoracic portion of the abdomen. It is made up of six lobes, the left medial, left lateral, right medial, right lateral, quadrate, and caudate lobes. Cranially the liver is convex in outline and lies, for the most part, in contact with the diaphragm. Caudally it is in contact with the right kidney at the renal fossa, the cranial flexure of the duodenum, and the stomach. The depth of the abdomen is greatest in this area. Its right border is formed by the right medial lobe cranially and the right lateral lobe and the caudate process of the caudate lobe caudally. Its left border is formed by the left medial lobe cranially and the left lateral lobe caudally. The quadrate lobe is centrally placed cranially. To the right and to the left the liver is adjacent to the abdominal wall. The gallbladder is situated in the right cranioventral abdomen.



Radiography


Because the liver lies in the deepest part of the abdomen at expiration, sufficient kilovoltage should be used to ensure adequate penetration. An impression of liver size can usually be gained from a study of plain radiographs of the abdomen. The location of the stomach often helps in evaluating liver size and position. A barium swallow may be required.



Normal Appearance


The exact outline of the liver is not discernible on plain radiographs of the abdomen. On a lateral radiograph, the liver occupies a triangular area between the diaphragm and the ventral body wall, the falciform ligament, and the stomach. Its caudal border, represented by the left lateral lobe, is sharp in outline and may project a short distance caudal to the ventral portion of the costal arch. Sometimes the liver shadow that contacts the stomach merges with that of the spleen, particularly on radiographs made in right lateral recumbency. This merging of shadows obscures the caudal limit of the liver. The liver lies somewhat more caudally in older dogs and may project beyond the costal arch.


On the ventrodorsal view, the liver appears as a homogeneous soft tissue opacity caudal to the diaphragm. Its outline is not well marked. Its caudal border on the right side may be determined from the position of the cranial duodenal flexure and the cranial pole of the right kidney in obese animals. Centrally the lesser curvature of the stomach marks its caudal limit. On the left it is covered by the fundus of the stomach. The caudal lobes of the lungs are superimposed on the liver to some extent on both lateral and ventrodorsal views, and pulmonary vessels are frequently seen superimposed on the liver shadow.


The exact position of the liver varies with respiration, being most caudally placed at full inspiration. Its position may also vary with the posture of the animal and with conformation. Right lateral recumbency allows the left hepatic lobes to move caudally, causing them to cast a larger shadow than in left lateral recumbency. Oblique views may produce an apparent rounding of the caudoventral edge. The liver appears larger in young dogs than in old ones.


The area of the falciform ligament appears larger on expiration than on inspiration. In the cat a distended gallbladder may protrude, simulating hepatomegaly. In obese cats, fat in the falciform ligament may displace the liver dorsally (Figure 2-7, A and B).



Ultrasonography


The animal is placed in dorsal recumbency for ultrasonography. If the patient is placed in lateral recumbency, both left and right recumbencies are used. For large dogs, the standing position may be used. Hepatic ultrasonography requires the cranial abdomen and occasionally the intercostal region to be clipped and prepared. The transducer is placed on the midline at the xiphoid cartilage, and a longitudinal or sagittal image is obtained by aligning the transducer plane parallel to the long axis of the animal and tilting the transducer in a cranial direction. Angling the transducer plane to the right or left sweeps the beam through the liver. Turning the transducer 90 degrees permits a transverse section. The entire liver is examined by angling the transducer steeply from a craniodorsal direction to a cranioventral one. Gas in the stomach may interfere with the examination. In large dogs with a deep-chested conformation, the liver lies more cranially. Interposition of the lung and stomach may give the impression of reduced liver size in such dogs. Small dogs or dogs with gas in the stomach may require an intercostal approach. This latter approach is also useful when specific areas of the liver are being examined and for fine-needle aspiration or biopsy. Moving the animal to displace the gas may be helpful, particularly if an intercostal approach is uninformative.


The hepatic tissue is loosely granular, with an even echotexture and echogenicity. The portal vessels are identified by their bright hyperechoic walls. Hepatic vessels are seen as anechoic linear and circular areas scattered throughout the liver. The hepatic arteries and bile ducts are not usually identified. The cranial border of the liver is identified as a hyperechoic curving border that represents the interface between the lungs and the diaphragm. Liver margins should be sharp and well defined. The relative echogenicity of the liver to adjacent and presumably normal organs should be compared to establish whether any marked abnormalities are present. The liver is hypoechoic compared with the spleen and equal to, or more echoic than, the kidney cortex. However, more than one organ may be abnormal, so comparative observations should be made with caution. The gallbladder is seen as a large pear-shaped anechoic structure on the right side of the liver. Sometimes granular sediment is present, particularly in fasting animals. Various artifacts may be associated with the gallbladder: acoustic enhancement, side-lobe artifact, and edge shadowing (see Chapter 1, pp. 17 and 19).


The caudal vena cava is identified in the midhepatic region traversing the diaphragm (Figure 2-7, G and H). The stomach is seen lying caudal to the liver. Gastric gas is identified as a hyperechoic region undergoing peristalsis within the stomach. The pylorus may be identified as a vaguely circular structure in the right ventral abdomen. The falciform fat that lies ventral to the liver may interfere with the liver examination. It has a variable echogenicity and a linear woven texture. In obese animals, image quality may be less than ideal. Ultrasonographic criteria for hepatic size are not reliable in inexperienced hands (Figure 2-7, C to G).



Abnormalities



Enlargement (Hepatomegaly)


Enlargement of the liver may be the result of cardiac incompetence (passive congestion), Cushing’s syndrome (hyperadrenocorticism), diabetes mellitus, primary or secondary neoplasia, inflammation, abscess or cyst formation, hyperplasia, infiltrative diseases such as lipidosis or amyloidosis, or engorgement with bile.



Radiologic Signs



1. Generalized enlargement is associated with rounding of the caudoventral edge, particularly that of the left lateral lobe on the lateral view.

2. There is a visible increase in size. The caudal liver edge projects farther beyond the costal arch than usual.

3. Displacement of structures related to the liver is seen.

4. The stomach is displaced caudally and dorsally on the lateral view and caudally and more often to the left on the ventrodorsal view. The cranial duodenal flexure, right kidney, stomach, and transverse colon are displaced caudally. The diaphragm may be displaced cranially and may show reduced excursion on fluoroscopy (Figure 2-8, A to F).

image image image image

Figure 2-8 A, Enlargement of the liver. The liver (arrowheads and arrow) is seen to extend well beyond the costal arch. B and C, Hepatomegaly. An 11-year-old domestic short-haired cat was suspected to have lymphosarcoma. The gastric silhouette is displaced caudally on both views by an enlarged liver. D, and E, Displacement of the stomach and duodenum by an enlarged liver. The full extent of the displacement is not obvious on the lateral view. This is a good example of the value of two views. A carcinoma of the bile duct was found at autopsy. The kidneys are displaced caudally.F, This 11-year-old Glen of Imaal Terrier presented with a history of seizures over the previous 24 hours. The animal was anemic and had an elevated alanine aminotransferase (ALT) level. The lateral radiograph shows a vaguely circular, large, soft tissue opacity caudal to the costal arch and pylorus. At surgery this proved to be a pedunculated tumor involving a single hepatic lobe. It was a hepatocellular carcinoma. G and H, This 9-year-old Springer Spaniel was in the late stages of heart failure. G, The hepatic veins (h) are markedly enlarged and extend deeply into the liver tissue (l). H, The liver margin (L) is enlarged and rounded (arrows) and is outlined by anechoic fluid (F) in the peritoneal cavity. The fluid was a transudate.I to O, Metastatic lesions in the liver have variable sonographic presentations, and not all parenchymal changes in the liver are pathologic. Fine-needle aspirates or biopsy is required to make a definitive diagnosis. I, Intraabdominal fluid (F) surrounds a bulbous protrusion (arrows) of a liver lobe (L). The hepatic margins are rounded. Poor skin contact has caused a reverberation artifact on the right corner of the image. J, A 6-year-old Retriever with ascites. Intraabdominal fluid (f) outlines a neoplastic hypoechoic nodule (arrows) at the tip of the liver lobe (l). s, Spleen; g, gallbladder. K, This is a paracostal view from the right side of the abdomen of a 10-year-old German Shepherd with ascites. A discrete circular mass (arrows) occupies the tip of the liver margin. This was a metastasis from a splenic hemangiosarcoma. The gallbladder (g) lies adjacent to the neoplasm. m, Mass; i, intestine; l, liver; f, fluid. L, A midline sagittal sonogram of the cranial abdomen in this dog shows multiple masses. Some are hypoechoic and hyperechoic (medium arrows). Others have a central hyperechoic region (short arrow) typical of a so-called target sign within the liver. These are multiple metastases. M, Hypoechoic metastatic masses of various sizes (arrows) are seen scattered throughout the liver. N, This lacy, hypoechoic pattern (arrows) is sometimes associated with metastatic disease. In this case it was caused by lymphoma.O and P, In some cases metastases may contain loculated anechoic areas. These are sagittal and transverse sonograms of a caudal liver lobe margin containing an anechoic fluid-filled septated mass (arrows). Diagnosis: hemangiosarcoma. Q, This 13-year-old Shetland Sheepdog presented with ascites. This lateral radiograph shows diffuse nodular mineralization throughout the hepatic parenchyma. Some isolated, focal, round, mineralized foci seen in the midventral abdomen are probably in the spleen. Serosal detail is poor in the cranioventral abdomen. The small intestine is displaced caudally. This is the same case as Figure 2-11, M. Diagnosis: diffuse hepatic disease. R, Hyperechoic circular nodules (white arrows) are seen throughout the liver of this cat. They were incidental findings and of no clinical significance and may be a result of parasitic infestation. Histopathologic confirmation was refused by the client.


Localized masses within the liver, depending on their size and location, can cause a variety of displacements of adjacent organs. In general, masses in the right side of the liver tend to displace the stomach and duodenum to the left and dorsally, and left-sided masses tend to displace the stomach and spleen to the right and dorsally. A mass originating in the right side of the liver can displace the tail of the spleen caudally. A mass originating in the caudate lobe of the liver can displace the right kidney caudally. Hepatic cysts may be mistaken for hepatic neoplasia because they may cause severe, focal hepatic enlargement (Figures 2-9 and 2-10, O). Liver masses can displace the small intestine caudally.


Discrete or diffuse mineral opacities are occasionally seen in the liver. They may be associated with neoplasia, granulomatous diseases, or parasites. Dystrophic calcification may be of no clinical significance (see Figure 6-1, E).



Ultrasonography


On ultrasonography the liver will appear enlarged with smooth margins. In patients with generalized hepatomegaly, the ventral aspect of the liver extends further caudally than is normal and makes the sonographic window for evaluation of the liver much larger. The liver may extend caudally as far as the umbilicus, so that if the probe is placed on the skin midway between the xiphoid and the umbilicus, the field of view is filled with liver. Hepatic enlargement can also be assessed by examining the caudate lobe of the liver and the right kidney. If the liver size is normal, the cranial pole of the right kidney sits in the renal fossa of the caudate lobe, and the depth of the caudate lobe and kidney are approximately the same. With severe generalized hepatic enlargement, the caudate lobe appears to partially surround the right kidney.


There may be a diffuse increased echogenicity and consequently poor definition of the portal vessels. Changes in echotexture and echogenicity fall broadly into the categories of diffuse or focal changes, with hyperechoic or hypoechoic features. The liver margins should be examined for changes in contour. Rounded edges are seen with hepatomegaly, and nodules may cause bulges on the margin. The presence of intraabdominal fluid outlines the liver edges, permitting small lesions to be seen. However, attribution of a histopathologic diagnosis to “typical” ultrasonographic features is not possible. Accurate diagnosis or confirmation of suspect changes or equivocal observations requires fine-needle aspirates or biopsies.


Diffuse changes can be the result of poor gain settings. A diffuse increase in echogenicity can occur as a result of generalized fatty infiltration, cirrhosis, lymphosarcoma, or steroid hepatopathy. Comparison with the echogenicity of the falciform fat may be helpful. A generalized reduction in echogenicity is associated with hepatic congestion or neoplasia (lymphoma). Diffuse parenchymal disease may be difficult to appreciate, and the appearance is not specific; fine-needle aspiration or biopsy is necessary for diagnosis.


Focal changes in the liver may be solitary or multiple. The echogenicity may vary from anechoic to hypoechoic to hyperechoic or may be mixed or complex and may have distinct or indistinct margins. Focal lesions contrast with the adjacent hepatic parenchyma. Focal lesions that can have variable echogenicity include benign nodular hyperplasia, hemorrhage, abscess, and neoplasia. Nodular hyperplasia is a benign lesion of decreased or increased echogenicity and is a common incidental finding. Focal changes may be seen with either metastatic or primary neoplastic infiltration, and they cannot be differentiated with certainty from benign lesions (Figure 2-8, I to P). Differential diagnosis should include hepatitis and cirrhosis. The so-called target sign, usually a hypoechoic rim surrounding a hyperechoic center, is produced by variations in tissue texture. It is the most consistent, but not a definitive, sign of neoplasia. The diagnosis of benign versus malignant neoplastic disease, or their differentiation from other focal lesions, requires fine-needle aspirate for cytologic evaluation or tissue core biopsy for histopathologic analysis. Fine-needle aspiration by ultrasonography permits the specific sampling of liver tissue and sequential examination of lesions for evaluation of treatment regimens (Figure 2-8, Q and R).


Hepatic cysts are usually anechoic, often congenital, and generally an incidental finding. Some cats with polycystic kidney disease may also have hepatic cysts. These may be single or multiple and are variable in size. The contents are usually anechoic, and the capsule is thin and cannot be distinguished from the liver parenchyma. Single large cysts can result in moderate or severe focal hepatic enlargement. Distal acoustic enhancement is a feature (see Figure 2-10, O).


Hepatic abscessation is an uncommon finding, and the lesion will vary in echogenicity depending on its stage of development. If gas is present, hyperechoic floccules may be seen oscillating in the lesion. Posterior distal acoustic enhancement is not usually a feature. The thickened abscess wall is usually ill defined and irregular. Occasionally it has a target appearance.


Distention of the hepatic veins may be seen with hepatic venous congestion such as occurs in right-sided cardiac failure. The distended anechoic vessels are seen extending peripherally into the hepatic tissues (Figure 2-8, G and H). The main vessels are seen to drain into the caudal vena cava in the craniodorsal hilar region. This junction often looks like a rabbit’s ears. Focal hemorrhage in the liver parenchyma, when fresh, is usually echogenic and gradually changes to a hypoechoic area as the lesion regresses.


Abdominal arteriovenous fistulas have been described in dogs. There may be associated ascites. The fistulas are seen as large, anechoic, tortuous vessels. Doppler ultrasound is required to differentiate these from portosystemic shunts.



Reduced Liver Size

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May 27, 2016 | Posted by in ANIMAL RADIOLOGY | Comments Off on The Abdomen

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