Small Animal Radiology and Ultrasound: A Diagnostic Atlas and Text

Major Classifications of Change. Radiographically detected lesions that affect the
small intestine may be considered to be diffuse or focal and either intraluminal, mural, or
extramural. Diffuse intestinal diseases include inflammation, diffuse neoplasms, immune
disease, lymphangiectasia, or hemorrhagic gastroenteritis. Focal intestinal diseases include
fungal granuloma and neoplasia.
Intraluminal. If intraluminal lesions are relatively small in diameter and short in
length, there may be little change in size or shape of the small intestine. On the GI series,
the only findings may be narrow linear filling defects within the lumen. These may be due
to ascarids, tapeworms, or linear foreign bodies of short length. In cases of relatively narrow-diameter,
long, linear foreign bodies, the GI series may reveal a small intraluminal filling
defect with plication or displacement of the small bowel (Fig. 3-109, A). In cases in
which the linear foreign body is relatively wide, the intraluminal filling defect will be seen
but plication will not be significant (Fig. 3-109, B). Most commonly, intraluminal lesions
may be identified because the intestine is dilated at a focal site in both the ventrodorsal and
lateral views, with a smooth and somewhat gradual zone of transition between the normal
diameter and the distention (Fig. 3-110). These lesions usually result in some degree of
intestinal obstruction. These range from partial, such as those seen with baby bottle nipples
that allow fluid and air to pass, to complete obstructions, as seen with very large foreign
bodies. Although foreign bodies are the most common intraluminal lesions, other
considerations must include pedunculated or sessile neoplasms that extend into the lumen.
Most intraluminal objects will allow the passage of contrast on all sides, while tumors that
protrude into the intestinal lumen will have at least one point of attachment to the wall.
Careful evaluation of the contrast column in all views may be required in order to discriminate
between luminal objects and those that arise from the intestinal wall. In many
cases, laparotomy will be required to determine the exact nature of the lesion.
Mural. Mural lesions can be categorized as those with thickening, those that have
ulcerations of the intestinal walls, or those with both. The normal bowel wall thickness
varies depending on whether it is at rest or actively involved in a peristaltic movement.
With full luminal distention and at rest, the bowel wall is normally a few millimeters thick.
The presence of thickened walls suggests infiltrative disease. The most common causes are
adenocarcinoma or intestinal lymphoma. Adenocarcinoma usually causes a concentric
narrowing (“napkin ring” or “apple core” or “parrot’s beak” appearance) of the intestinal
lumen and thickening of the wall over a length of a few centimeters, which leads to an area
of nearly compete intestinal obstruction (Fig. 3-111). 386 The normal bowel proximal to the
lesion may be dilated. The diameter of the bowel distal to the lesion is usually normal.
Lymphoma may occasionally cause concentrically thickened and distorted intestinal walls
with varying effects on the lumen diameter, but more commonly it extends over several
centimeters and is not completely circumferential. This multifocal regional variation in
wall thickness has been termed thumbprinting. In dogs, lymphosarcoma may appear as
irregular, small, focal asymmetric thickened areas of the small intestinal wall that neither
have a concentric pattern nor result in obstruction (Fig. 3-112). This may be difficult to differentiate
from some normal variations, but the repeatability of imaging the lesion is a
strong clue. In cats, the more common sign of lymphosarcoma is thickening of the intestinal
walls with luminal dilation. Involvement of the lymph nodes at the ileocolic junction
with minimal radiographic changes is also frequently seen. There may be an obstruction
proximal to the lesion with dilation of the small bowel.
The other form of mural disease is ulceration. An ulcer may be seen during a contrast
study as a crater-like or linear outpouching of the contrast column. The intestinal wall
may be thickened. A ring-shaped radiolucent defect with a central contrast-containing
portion may be observed also when the ulcer is chronic. This diagnosis is particularly difficult
to establish in the dog’s duodenum due to the normal presence of pseudoulcers (Fig.
3-113). Representing areas between accumulations of gut-associated lymphoid tissues
(GALT) in the descending and transverse duodenum, pseudoulcers are seen radiographically
as outpouchings of the barium from the normal duodenal lumen. 387 They are typically
on the antimesenteric surface. This may be of little help radiographically, because the
bowel may rotate on its normal axis and make identification of the mesenteric attachment
difficult.
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