Today's Veterinary Practice

SEP-OCT 2018

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CLINICAL INSIGHTS todaysveterinarypractice.com SEPTEMBER/OCTOBER 2018 63 The ileum is the thickest portion of the small intestine in the cat. The feline ileum has thicker muscularis and submucosal layers compared to the mucosal layer. The cat has a common opening to the ileum, cecum, and colon called the ileocecocolic junction, whereas the dog has separate ileocolic and cecocolic junctions. The feline cecum is usually not gas filled and is therefore small and identifiable as the ascending colon is traced in the sagittal or transverse imaging plane caudal to the ileocecocolic junction in the right cranial to mid abdomen. As in dogs, the colon is the thinnest gastrointestinal segment and can be traced from the pelvic inlet to the ileum. ABDOMINAL LYMPH NODES Dog The jejunal and medial iliac lymph nodes can be routinely seen in dogs. The medial iliac lymph nodes are fusiform and are found lateral to the caudal abdominal trifurcation into the external iliac arteries and continuation of the caudal abdominal aorta ( FIGURE 15A ). The jejunal lymph nodes are elongated, oval structures surrounding the caudal mesenteric artery and vein and are seen to the right of midline at the level of the umbilicus. These lymph nodes are much larger in puppies and can be lobulated and have hypoechoic peripheral areas ( FIGURE 15C ). The jejunal lymph nodes are hypoechoic relative to the surrounding mesenteric fat. Cat In cats, normal medial iliac lymph nodes ( FIGURE 15B ) are often not seen. The jejunal lymph nodes are found to the right of the umbilicus, medial to the ileocecocolic junction and adjacent to the cranial mesenteric portal veins. These lymph nodes are oval or bean shaped and hypoechoic to the surrounding mesentery. The ileocolic lymph nodes in the cat are seen adjacent to the ileocecocolic junction and typically measure <3 mm in width. These lymph nodes are often enlarged and infiltrated when round cell neoplasia is present. SUMMARY Ultrasound differences between the dog and cat are important to recognize. When performing a thorough abdominal exam in either the dog or cat, one must keep these normal anatomic variations in mind to ensure accurate descriptions of ultrasound abnormalities that might be seen. References 1. Mattoon J, Nyland T. Small Animal Diagnostic Ultrasound 3 rd ed. St. L ouis: Elsevier Saunders; 2015. 2. Mareschal A, d'Anjou MA, Moreau M, et al. Ultrasonographic measurement of kidney-to-aorta ratio as a method of estimating renal size in dogs. Vet Radiol Ultrasound 2007;48:434-438. 3. Barella G, L odi M, Sabbadin LA, et al. A new method for ultrasonographic measurement of kidney size in health dogs. J Ultrasound 2012;15(3):186-191. 4. D'Anjou MA, Bedard A, Dunn ME. Clinical significance of renal pelvic dilatation on ultrasound in dogs and cats. Vet Radiol Ultrasound 2011;52(1):88-94. 5. Geisse AL, Lowry JE, Schaeffer DJ, et al. Sonographic evaluation of urinary bladder wall thickness in normal dogs. Vet Radiol Ultrasound 1997;38:132-137. 6. Soulsby SN, Holland M, Hudson JA, et al. Ultrasonographic evaluation of adrenal gland size compared to body weight in normal dogs. Vet Radiol Ultrasound 2015;56(3):317-326. 7. Penninck DG, Zeyen U, Taeymans ON, et al. Ultrasonographic measurement of the pancreas and pancreatic duct in clinically normal dogs. Am J Vet Res 2013;74(3):433-437. K Figure 13. Gastrointestinal tract of a normal dog. Note the different wall layering of each segment and the overall differences between them. (A) Note the normal rugal folds within the fundic lumen. The hyperechogenicity with reverberation artifact represents gas within the lumen of the stomach. (B) The body of the stomach typically contains fewer rugal folds than the fundus. (C) The pyloroduodenal angle is depicted an abrupt transition, clearly delineating the gas-filled pylorus and empty duodenum in this patient. (D and E) The duodenum in a normal dog has a prominent mucosal layer (hypoechoic) compared to the jejunum. The normal anatomic location of the duodenum (along the right lateral body wall) and its ultrasonographic appearance aid in differentiation from the jejunum. (F and G) The jejunum is typically located throughout the midabdominal cavity and normally has a thinner mucosal layer (hypoechoic) than the duodenum. (H) The ileocolic junction (ICJ) is an abrupt transition from the ileum to the colon. The ileum is usually empty, and the colon is usually gas filled. (I) The lumen of the empty ileum can be likened to spokes on a wagon wheel. (J and K) The colon has a thin wall and usually contains gas that appears hyperechoic with dirty shadowing and fecal matter that results in attenuation of the ultrasound beam. LONG AXIS

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