Elodie E. Huguet1, Clifford R. Berry2, and Robson Giglio3 1 Department of Small Animal Clinical Sciences, College of Veterinary Medicine, University of Florida, Gainesville, FL, USA 2 Department of Molecular Biomedical Sciences, College of Veterinary Medicine, North Carolina State University, Raleigh, NC, USA 3 College of Veterinary Medicine, University of Georgia, Athens, GA, USA A wide range of normal variants are encountered when imaging the abdomen, and an understanding of the normal anatomy is important to recognize these variations. Various inherent and technical factors may influence interpretation of the normal anatomy, such as patient conformation, breed, and positioning. Some variations may mimic disease and should be interpreted with caution. To help guide image interpretation of the abdomen, an overview of the abdominal anatomy and commonly encountered variations are presented in this chapter (see also Appendix III). The abdomen is bordered cranially by the diaphragm and caudally by the pelvic canal. The abdominal surface of the diaphragm is mostly border effaced by the liver on radiographs but increased intraperitoneal fat (falciform ligament in cats) or decreased size of the liver can improve delineation of the dorsal or ventral diaphragmatic margins (Figure 20.1). The normal margins of the diaphragm are smooth and continuous, with a convex contour extending cranially into the thoracic cavity (Figure 20.2). The diaphragmatic crura attach on the ventral aspects of the L3–L4 vertebral bodies; these margins will be ill defined compared to L2 and L5 (Figure 20.3). Between left and right lateral radiographs of the abdomen, variations in the position of the diaphragmatic crura are observed that will vary with species, patient breed and size, and x‐ray beam centering. Due to gravitational displacement of the abdominal structures on lateral radiographs, increased intraabdominal pressure results in cranial displacement of the dependent diaphragmatic crus in relation to the contralateral nondependent diaphragmatic crus. On the right lateral projection, the diaphragmatic crura are parallel to each other, whereas on the left lateral projection, they are often tangentially oriented, diverging away from a central position, creating a V‐ or Y‐shaped appearance (Figure 20.4). A similar variation should be taken into consideration when imaging patients in lateral recumbency with other imaging modalities (Figure 20.5). FIGURE 20.1 Increased delineation of the diaphragm on a left lateral radiograph associated with the presence of increased intraabdominal fat. FIGURE 20.2 Computed tomographic image of the diaphragm in a dorsal plane. FIGURE 20.3 Radiograph of the diaphragmatic crura attachment on the ventral aspects of the L3–L4 vertebral bodies (note ill‐defined ventral margin). FIGURE 20.4 Displacement of the diaphragmatic crura on right (A) and left lateral (B) radiographs, respectively. FIGURE 20.5 Computed tomographic images of the diaphragmatic crura in a dorsal plane, showing similar cranial extension of the diaphragmatic crura in right lateral recumbency (A ‐ RLAT) where gas is present in the fundic portion (Label F) of the stomach. In (B LLAT) there is gas noted in the pylorus (P) and the left diaphragmatic crus is displaced cranially relative to the right. The fundus (F) of the stomach is filled with fluid. On ultrasound, the diaphragm cannot be isolated from the highly reflective hyperechoic interface of the lungs in the absence of pleural disease (Figure 20.6). The reflective interface of the lung–diaphragm usually causes a mirror image artifact, resulting in an image of abdominal structures (e.g. liver and gall bladder) noted on the thoracic side of the diaphragm (Figure 20.7). The abdomen and pelvic cavities, as well as the scrotum in male patients, form a continuous peritoneal cavity. The wall of the peritoneal cavity is composed of the peritoneum, which has three parts (Figure 20.8). FIGURE 20.6 Indistinction of the diaphragm from the lung interface on ultrasound. The retroperitoneal space is a potential space between the dorsal parietal peritoneum and the hypaxial musculature. It extends from the diaphragm and extends into the pelvic cavity. Cranially, the retroperitoneal space and mediastinum communicate through the aortic hiatus, meaning that a pneumomediastinum can lead to a pneumoretroperitoneum. Contained within the retroperitoneal space are the kidneys, adrenal glands, ureters, cisterna chyli, major abdominal blood vessels, and parietal lymph nodes. In female dogs, the retroperitoneum includes part of the urinary bladder neck, unlike in male dogs where it extends more ventrally at the level of the pelvic inlet to include the ventral margin of the prostate. FIGURE 20.7 Mirror image artifact from the reflective interface of the lung–diaphragm on ultrasound. FIGURE 20.8 Anatomic illustration of the peritoneum and associated spaces. The amount of fat present throughout the abdominal cavity depends on the patient’s body condition. In obese patients, increased fat deposition may be observed predominantly around the falciform ligament and retroperitoneal space. The presence of fat in the peritoneal cavity aids with visualization of the serosal margins on abdominal radiographs (Figure 20.9). This is attributed to the lower density of fat in relation to fluid and/or soft tissues within adjacent structures. Younger patients have a greater amount of brown fat with a higher water content and a mild amount of peritoneal effusion, both of which will result in an increase in soft tissue opacity throughout the abdominal cavity, thereby decreasing the overall serosal detail (Figure 20.10). Additionally, poor serosal detail is seen in emaciated patients due to the reduced presence of intrabdominal fat (Figure 20.11). FIGURE 20.9 Right lateral radiograph with good conspicuity of the serosal margins associated with the presence of a large amount of intraabdominal fat. When evaluating the abdominal cavity with ultrasound, excess fat may partially attenuate the ultrasound beam, therefore limiting visualization of deeper abdominal structures, and can hinder the ultrasonographic evaluation of larger patients, making computed tomography a preferred modality (Figures 20.12 and 20.13). A scant amount of anechoic effusion within the peritoneal cavity represents a normal physiological variant, especially in young cats and dogs. Within the peritoneal cavity, the fat may undergo focal necrosis and form a mobile intraabdominal mineralized body with a thin mineralized rim, called “Bates bodies,” nodular fat necrosis or cholesterol inclusion cysts. These structures vary in size and location, and are of no clinical concern (Figure 20.14). FIGURE 20.10 Radiograph of a juvenile canine patient with poor serosal detail due to the presence of brown fat and mild amount of physiologic peritoneal effusion. FIGURE 20.11 Radiograph of an emaciated patient with poor serosal detail due to the reduced presence of intraabdominal fat. FIGURE 20.12 Radiograph (A) and ultrasound (B) images of the same cat with a large amount of falciform fat, causing attenuation of the ultrasound beam. Ultrasound image (C) of a normal feline liver for comparison. FIGURE 20.13 Improved assessment of the liver using computed tomography as opposed to ultrasound in obese patients. FIGURE 20.14 Right lateral radiograph of a feline patient with a ventrally located intraperitoneal mineralized structure, representing a Bates body. Radiographs are commonly used to assess the luminal contents of the gastrointestinal tract. The normal amount of gas within the gastrointestinal tract is variable. In normal fasted cats, small intestinal gas is rarely to mildly present, whereas in fasted dogs, approximately 30–60% of the small intestinal segments may be filled by gas under normal conditions. In nonfasted dogs and cats, the amount of intraluminal small intestinal gas may increase. The normal gastrointestinal wall cannot be reliably assessed due to border effacement with luminal contents or lack thereof and crowding with adjacent abdominal structures. Ultrasonography provides the best evaluation of the normal gastrointestinal wall; however, the presence of intraluminal gas may hinder visualization of the wall in the far field. The patient may need to be changed to a different recumbency for a more complete evaluation of the wall layers in such instances when doing an abdominal ultrasound. The stomach has four regions: fundus, cardia, body, and pylorus (Figure 20.15). The craniodorsal and caudoventral surfaces of the stomach between the gastroesophageal and gastroduodenal junctions form the lesser and greater curvature, respectively. The stomach is located caudodorsal to the liver with the fundus/body centered in the left cranial abdomen. The pyloric antrum is ventrally located in relation to the fundus and extends to the right of midline in dogs (Figure 20.16). In comparison, it may be positioned along midline in cats (Figure 20.17). The stomach may contain a small amount of fluid and gas in fasted patients. Gas shifts within the nondependent aspect of the gastric lumen per recumbency as illustrated in Figure 20.18. Filling of the pyloric antrum with gas on the left lateral projection may aid with visualization of the gastroduodenal junction, which may contain a small amount of gas tracking into the proximal duodenum under normal conditions (Figure 20.19). Gas within the gastric lumen in an underdistended stomach may contrast with rugal folds along the mucosal margins of the gastric wall, which are commonly most prominent in the gastric body and fundus (Figure 20.20). This finding is less commonly seen in cats. The size of the stomach varies based on the fasted state of the patient. In the absence of hepatomegaly, the caudal border of a relatively empty stomach should not extend beyond the last pair of ribs (Figure 20.21). FIGURE 20.15 Anatomic illustration of the canine and feline stomach. FIGURE 20.16 Normal positioning of the stomach in dogs on a ventrodorsal radiograph. FIGURE 20.17 Normal positioning of the stomach in cats on a ventrodorsal radiograph. Ultrasound has the unique advantage of providing the best evaluation of the gastric wall layers, which are named and characterized as follows (from lumen to serosal surface, Figure 20.22). FIGURE 20.18 Normal distribution of gas in the nondependent aspect of the stomach on right lateral (A), left lateral (B) and ventrodorsal projections (C). CT images in the corresponding right recumbent (D), left recumbent (E), and dorsal recumbent (F) position show gas in different parts of the stomach depending on body position. Measurements of the gastric wall thickness may be limited in the presence of an empty stomach and should be obtained with caution when only containing a small amount of ingesta as redundancy of the gastric wall may be falsely interpreted as gastric wall thickening (Figure 20.23). The overall thickness of the gastric wall should be measured between rugal folds and is <5 mm in dogs and <4 mm in cats [1]. The muscularis propria is thickest at the level of the pyloric sphincter and should not be misinterpreted as pathologic thickening. While the gastric wall layers cannot be visualized on radiographs, cats have submucosal fat, which may be apparent on ventrodorsal projections when the gastric body is empty and viewed enface (Figure 20.24) [2]. FIGURE 20.19 Tracking of nondependent gas within the pyloric antrum, through the pyloroduodenal junction and into the descending duodenum on a left lateral radiographic projection. FIGURE 20.20 Empty stomach with a small amount of intraluminal gas, highlighting normal rugal folds, on right lateral (A), left lateral (B) and ventrodorsal (C) radiographs. FIGURE 20.21 Normal nondistended stomach on a right lateral radiograph (note how caudal margin of the stomach does not extend beyond the last pair of ribs). FIGURE 20.22 Normal gastric wall layers on ultrasound. Computed tomography (CT) has the advantage of providing a three‐dimensional image of the stomach without superimposition of other structures, permitting evaluation of the gastric wall despite the presence of intraluminal gas. CT may also improve evaluation of the stomach in large and/or deep‐chested patients. While distinct wall layers are poorly recognized, the normal increased contrast enhancement of the gastric mucosa on images acquired during the arterial phase may help differentiate it from the other gastric wall layers (Figure 20.25). The small intestine has three parts, which sequentially are the duodenum, jejunum, and ileum when traced in an aborad direction. The duodenum is divided into descending and ascending parts. The descending duodenum extends caudally along the right lateral abdominal wall in the dog and then turns craniomedially at the caudal duodenal flexure before continuing for a short distance as the ascending duodenum. The ascending duodenum then joins with the jejunum in the mid to cranial abdominal region near midline. The jejunum makes up the majority of the small intestine and mostly occupies the mid abdomen. In cats, the pyloroduodenal junction is near midline so that the descending duodenum is in a more midline position compared with dogs. In cats with abundant fat and increased fecal material in the colon, most of the small intestine may be located to the right of midline. The ileum is the shortest small intestinal segment and cannot be differentiated from the jejunum on radiographs aside from localization at the ileocolic junction in dogs and the ileocecocolic junction in cats. FIGURE 20.23 Radiographic (A, B) and ultrasonographic (C) appearance of a normal empty stomach with a prominent wall due to mural contraction and presence of rugal folds. The small intestine has indistinguishable wall layers on radiographs with effaced mucosal margins in the absence of intraluminal gas. The overall thickness of the duodenum is often greater than the jejunum in dogs. The descending duodenum may contain a small amount of gas, especially on the left lateral projection due to extension of nondependent gas from the gastric lumen. Along the antimesenteric side of the duodenum, gas or positive contrast medium within the duodenal lumen may highlight small concave mucosal defects representing pseudoulcers secondary to gut‐associated lymphoid tissue (GALT) or Peyer’s patches (Figure 20.26). A similar finding may be observed with ultrasonography and CT (Figure 20.27). In cats, the small intestine may be evenly concentrically narrowed with a “string of pearls” appearance, representing peristalsis (Figure 20.28). On ultrasound, the small intestine has well‐defined wall layers, similar to the stomach, with normal wall layer thickness measurements listed in Table 20.1 [1]. The ileum may be differentiated from the jejunum due to its overall increased wall thickness and prominent submucosa and muscularis layers (Figure 20.29). In young patients, hyperechoic lines parallel to the submucosal may be observed within the outer aspect of the mucosa and may represent normal lymphoid tissues (Figure 20.29b). When viewing any portion of the small intestine in a short axis view, wedge‐shaped hyperechoic regions are seen extending from opposing sides of the lumen into the mucosa and likely represent anisotropism due to tangential ultrasound beam alignment with the intestinal villi and intestinal crypts (Figure 20.30). Occasionally, hyperechoic striations along the luminal aspect of the mucosa may represent gas or ingesta within the intestinal crypts, most commonly seen in nonfasted patients, and may be indistinguishable from pathologic lymphangiectasia (Figure 20.31). FIGURE 20.24 Radiographic (A), ultrasonographic (B), and computed tomographic (C) appearance of the feline gastric wall with prominent submucosal fat (decreased opacity on radiographs, increased echogenicity on ultrasound and decreased attenuation on the CT study). FIGURE 20.25 Transverse computed tomographic images of the stomach acquired during the arterial (A) and venous (B) phases of contrast enhancement. Similar to the stomach, the small intestinal wall layers cannot be differentiated on CT, with the exception of the mucosa following IV contrast due to normal increased contrast enhancement during the arterial phase (Figure 20.32). The colon is divided into ascending, transverse, and descending parts. The ileocecocolic (in cats) or ileocolic junction (in dogs) is commonly located in the right cranial to mid abdomen. At this level, the cecum represents a blind pouch which joins the ileocecocolic transition (in cats) or the ascending colon to form the cecocolic junction (in dogs). The ascending colon can be identified within the right cranial abdomen and traced cranially from the ileocolic junction to the right colic flexure, where it turns into the transverse colon. The transverse colon extends across midline into the left cranial abdomen before turning at the left caudal flexure and continuing caudally as the descending colon to the level of the pelvic inlet. The descending colon is more commonly located within the left abdomen but can be incidentally redundant and traced to the right of midline (Figure 20.33). The cecum and colon cannot always be differentiated on radiographs. When seen, the cecum often represents a lobular gas‐filled structure in the right midabdominal region (Figure 20.34). Occasionally, fecal material may be identified within the cecum. FIGURE 20.26 Radiographs of the stomach acquired before (A) and after (B) barium administration, highlighting small concave defects along the duodenal mucosa, most compatible with gut‐associated lymphoid tissue or Peyer’s patches. FIGURE 20.27 Ultrasonographic (A) and computed tomographic (B) images of the duodenum, showing the presence of small concave mucosal defects, representing gut‐associated lymphoid tissue or Peyer’s patches. On radiographs, the cat cecum is not visualized. On ultrasound, the feline cecum may also be difficult to differentiate from the colon and represents a blind pouch continuous with the colon at the level of the ileocecocolic junction. When empty, the cecum in feline patients forms a lobular hypoechoic structure (Figure 20.35). The colonic contents can have a wide range of appearances and should be primarily heterogeneously soft tissue opaque. FIGURE 20.28 Right lateral (A) and ventrodorsal (B) radiographs of normal small intestinal peristalsis in cats (e.g., “string of pearls” appearance). TABLE 20.1 Normal wall layer thickness in dogs and cats. There are no quantitative criteria establishing the normal colonic diameter in dogs on radiographs. In cats, a maximal colonic diameter to L5 vertebral length ratio of less than <1.28 is most representative of a normal colon [3]. When differentiation of the colon from the small intestine is limited, especially in the present of abnormal small intestinal dilation, a pneumocolonogram may be considered by rectally injecting the amounts of room air listed in Table 20.2 into the colon with a catheter tip syringe (Figure 20.36). On ultrasound, the colon has a thin wall with similar wall layers as the remainder of the gastrointestinal tract, cumulatively measuring up to 1.5 mm in maximal thickness. Some variation in wall thickness may be observed in direct correlation with the amount of colonic distension present. Within the colonic submucosa in canine and feline patients, small, well‐defined, rounded to ovoid and hypoechoic micronodules (1–3 mm in size) have been described to represent lymphoid follicles [4]. The clinical significance of these follicles remains unknown, representing an incidental finding or a reactive inflammatory/infectious response (Figure 20.37) [4]. The pancreas is located just caudal to the stomach and is composed of left and right lobes situated along the greater curvature of the stomach and mesenteric side of the descending duodenum, respectively [5–8]. The body of the pancreas is centered between the two lobes at the level of the pylorus. It is contradictory among anatomists if a true pancreatic body is present in cats. In dogs, the normal pancreas cannot be visualized on radiographs. In contrast, the left pancreatic lobe in feline patients can occasionally be seen extending between the gastric fundus and splenic head/body, particularly with increased adiposity within the peritoneal cavity (Figure 20.38). The pancreas represents a thin, long and mildly lobular soft tissue opaque structure. Using ultrasound, the right pancreatic lobe and body are readily identified in dogs and cats. In large patients or in the presence of gastric distension, the left pancreatic lobe may not be readily visualized in dogs. The entire pancreas is more reliably identified in cats. The pancreas should be relatively well demarcated with an echogenicity slightly less than the surrounding fat, but higher than the liver (Figure 20.39). The pancreas may be infiltrated with fat in obese patients and have an echogenicity similar to the mesenteric fat, rendering visualization more difficult (Figure 20.40). The mean normal thickness of the pancreas (dorsal to ventral dimension) is listed in Table 20.3 [9]. FIGURE 20.29 (A) Ultrasound image of normal jejunal wall layers in a dog. (B) Ultrasound image of normal ileal wall layers in a dog with the presence of a parallel hyperechoic mucosal line, representing normal lymphoid tissues. FIGURE 20.30 Transverse ultrasound image of the duodenum with artefactual bilateral regions of mucosal hyperechogenicity, representing anisotropy. The use of ultrasound contrast agents may improve visualization of the pancreas in both canine and feline patients and can be used to evaluate normal perfusion [4, 5]. The limited availability and cost of ultrasound contrast agents currently limit the use of this technique in veterinary patients, but may be of future benefit to recognize pathological pancreatic changes. Using ultrasound and CT, the pancreatic duct can occasionally be seen extending centrally within the left and right pancreatic lobes (Figure 20.41). In dogs, the extrahepatic bile duct and pancreatic duct separately enter the duodenum at the major duodenal papilla. In cats, the extrahepatic and pancreatic ducts join together just before entering the major duodenal papilla. The accessory pancreatic duct enters the duodenum at the minor duodenal papilla and is the main excretory duct in dogs. Normal upper reference ranges of <3 mm and <4 mm in diameter are reported in dogs and cats, respectively [9]. In older cats greater than 10 years of age, the normal pancreatic duct may be larger, measuring up to 5 mm in diameter (Figure 20.42) [10]. FIGURE 20.31 Longitudinal ultrasound images of two small intestinal segments, containing mucosal hyperechoic striations (A), which represent gas or ingesta within the intestinal crypts, commonly seen in nonfasted dogs, and may be indistinguishable from pathologic lymphangiectasia. In (B), hyperechoic mucosal speckles are also present noted in a nonfasted dog. FIGURE 20.32 Transverse computed tomographic images centered on the small intestine and acquired precontrast (A) and during the arterial (B), venous (C), and delayed (D) phases of contrast enhancement. FIGURE 20.33 Ventrodorsal radiographic projection of a redundant colon, as characterized by rightward deviation of the descending colon in the caudal abdomen. FIGURE 20.34 Ventrodorsal radiograph showing a lobular and gas‐filled bowel segment in the right midabdominal region, which represents a normal canine cecum. FIGURE 20.35 Normal ultrasonographic appearance of the feline cecum. TABLE 20.2 Recommended volumes of room air for pneumocolon negative contrast studies. On CT, the normal pancreas is soft tissue attenuating with a density lower than the liver and mean HU value of 61 in dogs and 48 in cats on precontrast images [7, 8]. Diffusely, the normal pancreas has heterogeneous arterial and homogenous venous contrast enhancement which remains slightly hypoattenuating to the liver during all phases of contrast enhancement. A peak attenuation value is observed during the venous phase in both cats and dogs with a mean HU value of 129 and 166, respectively (Figure 20.43) [7, 8]. The gall bladder is a large saccular structure located within the gall bladder fossa of the liver, which is composed of the quadrate lobe of the liver medially and the right medial lobe laterally. The gall bladder communicates with the intrahepatic bile ducts via the cystic duct before continuing as the extrahepatic bile duct at the level of the porta hepatis. It continues caudally to the major duodenal papilla, that then enters the lumen of the proximal duodenum. While the normal gall bladder is routinely not identified on radiographs, it may occasionally represent a rounded focal soft tissue opaque bulge along the ventral margin of the liver in obese cats (Figure 20.44). The size of the gall bladder is highly variable and may be quite voluminous in fasted or anorexic patients. Therefore, gall bladder size cannot be reliably used as an indicator of pathologic distension. In cats and dogs, the gall bladder is variable in size and shape and in normal cats it can be bilobed (Figure 20.45). Ultrasound is the preferred modality to evaluate the gall bladder. The normal gall bladder contains anechoic bile and has a thin and smoothly marginated hyperechoic wall, which measures less than 1 mm in thickness under normal conditions in cats and up to 2–3 mm in dogs [11, 12]. Contrast‐enhanced ultrasonography has been reported as a way to increase the conspicuity of the gall bladder wall and may aid in the identification of wall defects due to necrosis or rupture [13]. Commonly, variable amounts of mobile, granular, echogenic and nonshadowing material, referred to as “sludge,” may be identified incidentally within the gall bladder lumen in dogs (Figure 20.46) [14]. The clinical significance of this finding in cats is unclear and has been suggested as a sequela of cholestasis. Gall bladder sludge may be recognized as more hyperattenuating nonmineralized material within the gall bladder lumen on CT (Figure 20.47). FIGURE 20.36 Ventrodorsal radiographs pre (A) and post (B) pneumocolon. Two mL/kg of room air was introduced into the colon and then an immediate exposure made for (B). FIGURE 20.37 Feline colon US image (long axis) with a thickened mucosal layer and lymphoid follicles. FIGURE 20.38 The tubular soft tissue opacity located between the spleen (craniolateral) and the left kidney (caudal) is the feline pancreas. Using ultrasound and CT, the cystic duct can be traced from the gall bladder and tapers before joining the intrahepatic bile ducts. The hepatic bile ducts represent thin branching tubular structures, which taper peripherally and can be differentiated from the hepatic vasculature using color or power Doppler. The extrahepatic bile duct is readily visualized, especially in cats, and should measure less than 5 mm in diameter in cats and 2 mm in dogs [15], although in dogs it is rarely seen under normal conditions. FIGURE 20.39 Three different ultrasound images without and with yellow highlights of the pancreas. (A) Short axis (transverse) view from the right cranial abdomen in a dog documenting the normal pancreas next to the duodenum. The duodenal papilla is partially visualized along the inside of the duodenum (medial margin, white arrow in (B)). Lateral is to the left. (C) Short axis (transverse) image from the right cranial abdomen in a normal cat. The right lobe of the pancreas extends toward the pancreatic body and the left lobe is noted (highlighted in yellow in (D)). Lateral is to the left. From the same cat (E), a transverse view documenting the left lobe of the pancreas (in long axis) as hypoechoic to the surrounding tissue (highlighted in yellow in (F)). Lateral is to the right of the image. In all images the pancreatic duct can be visualized. The liver is one of the largest intraabdominal organs and occupies the majority of the cranial abdominal cavity, with a larger portion extending to the right of midline. The liver is bordered cranially by the diaphragm and caudally by the stomach. Additionally, the caudate lobe of the liver conforms to the cranial pole of the right kidney to form the renal fossa (Figure 20.48). On radiographs, the liver is homogeneously soft tissue opaque with an angular caudoventral border, which as a general rule should not extend caudally beyond the costal arch in the absence of hepatomegaly (in expiratory radiographs) (Figure 20.49). Some variations may be seen in the presence of pulmonary hyperinflation, gastric distension or due to variability in body conformation. The position of the gastric axis, representing a line drawn from the gastric fundus to the pylorus on lateral radiographic projections, may also be used to assess liver size. Although some variations may exist, the gastric axis should be parallel to the long axis of the last ribs (Figure 20.50). Similar criteria are used to assess liver size in cats; however, the position of the pylorus tends to differ by being more medially positioned on ventrodorsal radiographic projections (Figure 20.51). FIGURE 20.40 (A) Short axis (transverse) view from the right cranial abdomen in a cat documenting a hyperechoic pancreatic right lobe next to the duodenum (highlighted in yellow in (B)). This is consistent with fatty infiltration. Lateral is to the left. TABLE 20.3 Normal thickness of the pancreas in dogs and cats. Liver size is difficult to assess with ultrasound. Under normal conditions, the liver should have a sharply marginated caudoventral border, which does not extend caudally beyond the gastric body (Figure 20.52).
CHAPTER 20
Anatomy, Variants, and Interpretation Paradigm
Introduction
Diaphragm
Abdominal cavity
Gastrointestinal Tract
Stomach
Small Intestine
Colon
Duodenum (mm)
Jejunum (mm)
Ileum (mm)
Dog
<15 kg
3.8
3.0
3.0
15–30 kg
4.1
3.5
3.5
>30 kg
4.4
3.8
3.8
Cat
2.2
2.2
2.8
Pancreas
Species
Volume (room air)
Dog
1–3 mL/kg
Cat
20–30 mL
Biliary System
Liver
Species
Right lobe
Body
Left lobe
Dog
8.1 mm
6.3 mm
6.5 mm
Cat
4.4 mm
6.2 mm
5.8 mm
Stay updated, free articles. Join our Telegram channel
Full access? Get Clinical Tree
