Small Animal Radiology and Ultrasound: A Diagnostic Atlas and Text

344 Small Animal Radiolo g y and Ultrasono graphy
Fig. 3-114 A 6-year-old spayed German Shepherd dog with vomiting
for 6 days. There is marked dilation and irregularity of the
descending and transverse duodenum as well as multiple ulcers
extending well beyond the normal intestinal serosal border (black
arrows). Differential diagnoses include ulcers due to mast cell tumor,
gastrinoma (Zollinger-Ellison syndrome), or idiopathic causes.
Diagnosis: Duodenal ulcers, secondary to gastrinoma causing hypersecretion
of gastric acid.
is either intramural or has invaded into the mucosal from the outside. Extramural lesions
usually are not due to disease of small bowel origin but indicate impingement by other
structures. One example of this type of lesion is adhesions from previous abdominal surgery
(Fig. 3-115). Enlarged ileocolic lymph nodes may produce an extramural compression
of the ileum or cecum. An extraluminal mass may arise from the intestinal wall and extend
outward to spare the intestinal lumen from compression (Fig. 3-116). This type of finding
is typical of intestinal leiomyosarcoma. These masses may contain gas densities if their centers
become necrotic and develop a communication with the intestinal lumen.
Extraluminal masses may occasionally cause intestinal obstruction, but rarely is the
obstruction complete, and in most cases contrast medium readily passes around the mass.
Ultrasonography of Small Intestinal Abnormalities. Ultrasonography can be used to
evaluate the size, shape, and wall thickness of the small intestine. 18,336 Often, only three layers
of the wall can be seen. Thickening of the small intestine can be detected most easily
when the thickening is asymmetric. The normal intestinal wall width ranges from 2 to 3
mm. 18 The wall of the duodenum is normally slightly thicker than the rest of the small
intestine and may be up to 4.5 mm thick. Variation in bowel wall thickness and diameter
occurs in association with normal peristalsis. Variation also has been associated along with
poor intestinal wall layer definition in cats with inflammatory bowel disease. 389 Because
peristalsis can be observed during the ultrasonographic examination, the change in bowel
diameter can be observed directly and dilation of the intestines can be documented. A lack
of peristalsis associated with intestinal dilation would be indicative of ileus. This can be
recognized during the ultrasonographic examination. 336 The major problem in detecting
small intestinal distention is distinguishing between the small intestine and the colon.
Active peristalsis indicates that the bowel is the small, not the large, intestine. The position
of the colon is usually fixed, and the course that the colon follows is usually straighter than
the small intestine. These are helpful, although they are not completely reliable, features.
Intraluminal, intramural, and extramural lesions can be detected using ultrasonography.
390-404 Intraluminal objects can be observed surrounded by mucus or normal intestinal
content. Most foreign objects are hyperechoic and cause shadowing (Fig. 3-117). 336,346
They may be masked by the presence of air within the intestinal lumen, but in most cases