Small Intestine

In the small bowel, Isospora belli, Cryptosporidium, and Microsporidia all produce a similar hypersecretory state on barium studies, causing dilution and fragmentation as well as fold thickening (Fig. 8.52A). Isosporiasis may involve the small intestine, the mesenteric and mediastinal lymph nodes, the spleen, and the liver. Abdominal involvement is common in disseminated histoplasmosis. The gastrointestinal tract will be involved 75% of the time; the terminal ileum and ascending colon are particularly often affected. This involvement is manifested by ulcerations, fold thickening, and marked circumferential bowel wall thickening resembling carcinoma.

The bowel may be involved in tuberculosis, particularly the ileocecal region, which is rich in lymphoid tissue. Ulcers, ulcerating masses, fistulae, stenoses, and wall thickening may be seen, producing obstruction, bleeding and perforation. Mycobacterium avium complex commonly involves the jejunum as well as the remainder of the small bowel, producing a pattern of irregular thickened folds (see Chapter 5 on Tuberculosis). Kaposi's sarcoma involving the small bowel may produce nodular fold thickening, often with the characteristic umbilicated lesions (Fig. 8.52B). The lesions are best demonstrated by compression (see Chapter 42 on Kaposi Sarcoma). Cytomegalovirus may also involve the small bowel, particularly the terminal ileum (Fig. 8.53 B).

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Fig. 8.52A, B (middle, right). The small intestine of AIDS patients is affected by infections and tumors. For example: (A) Isospara belli causes thickening of the mucosal folds and dilution of barium. (B) There may be multiple nodules in the small intestine in patients with Kaposi's sarcoma (arrows), often associated with thickened mucosal folds. If the nodules ulcerate, they appear as "target" lesions.

Colon and Rectum

Cytomegaloviral colitis is common, often involving the cecum and ascending colon. As in the esophagus, multiple deep or shallow ulcers are produced (Fig. 8.53), often associated with a markedly thickened bowel wall and inflammatory changes in the adjacent fat. Pneumatosis coli or perforation may result. Histoplasmosis may produce fold thickening and apple-core lesions in the ileocecal region. Rectal involvement may be seen in herpes simplex virus infections.

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Fig. 8.53 A-C. Cytomegaloviral infection of the colon. (A) Multiple ulcers with surrounding edema (arrows), seen in a barium air-contrast study, and (B) marked thickening of the bowel wall in a patient with both enteritis and colitis. (C) In another patient there is pneumatosis coli (arrow). This is relatively common in AIDS. The differential diagnosis includes cryptosporidiosis, rotavirus, Clostridium difficile and Pseudomonas infections. (C courtesy of Dr. William Brandt).

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