Small Animal Radiology and Ultrasound: A Diagnostic Atlas and Text

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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. Chapter Three The Abd omen 339
340 Small Animal Radiolo g y and Ultrasono graphy Fig. 3-109 A, A 1-year-old male Coonhound with anorexia, depression, vomiting, and diarrhea for 2 weeks. The 30-minute lateral view revealed marked plication of the majority of the small intestine. This appearance is most consistent with a linear foreign body of small to intermediate diameter. Diagnosis: Small intestinal linear foreign body (sewing thread). B, A 3-year-old neutered male domestic shorthaired cat with vomiting and anorexia for 2 days. The survey radiographs revealed no abnormalities. The ventrodorsal view taken at 30 minutes into the GI series revealed mild dilation of the small intestine and an irregular lucent filling defect that extends over a significant length of small intestine and is best seen in the loops in the left portion of the abdomen (open white arrows). No plication is seen. Linear foreign bodies that have a wide diameter do not cause the bowel to plicate but rather act as any other foreign body that causes a partial small intestinal obstruction. Diagnosis: Small intestinal linear foreign body (athletic shoelaces). A B Pathologic ulcers may occur with or without concurrent mural thickening. 388 One of the more common causes of small intestinal ulceration is mast cell tumor. This frequently is associated with intestinal wall thickening and most commonly is seen in the duodenum. Nonsteroidal antiinflammatory drugs may also cause intestinal ulceration. Another cause of intestinal ulceration that is rarely seen is the Zollinger-Ellison syndrome. This syndrome,
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SAUNDERS An Imprint of Elsevier Sci
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C H A P T E R O N E Introduction GE
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Chapter One Introduction 3 Fig. 1-1
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metal. Soft tissues or organs surro
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A B C Fig. 2-63 A 10-year-old male
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100 Small Animal Radiolo g y and Ul
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Fig. 2-101 A 7-year-old male mixed
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Fig. 3-234 A 7-year-old female Brit
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Fig. 4-59 A 9-year-old female Russi
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Fig. 4-73 A 2-year-old female Saint
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Fig. 4-97 A 10-year-old male mixed
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Fig. 4-107 A 4-year-old male Chow C
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I N D E X A Abdomen, abnormal prese
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Index 729 Bone, cysts of, 525-527,
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Index 731 Ear, abscess of—cont’
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Index 733 Hydrocephalus—cont’d
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Index 735 Lungs. See also Pulmonary
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Index 737 Pregnancy, determination
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Index 739 S-shaped aortic deformity
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Small Animal Radiology and Ultrasound: A Diagnostic Atlas and Text

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