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but the majority of these infections are due to MAC in developed nations of Europe and North
America, while most are due to MTB in Africa.[687]
With MAC infection, the mucosa may grossly show small pinpoint yellow foci, fine
white nodules, diffuse yellow patches, or raised yellow plaques. This yellow color is explained
by the microscopic appearance of numerous striated blue macrophages distending the intestinal
mucosal villi. Acid-fast stain shows the macrophages to be filled with numerous mycobacteria.
Even PAS stain may reveal the organisms and give an appearance that resembles Whipple's
disease.[688] A common radiographic finding is diffuse thickening of jejunal folds without
ulceration.[416]
Mycobacterium tuberculosis in the GI tract is distributed primarily as small granulomas
in cases with widespread dissemination. The most common site of involvement for MTB is the
ileocecal region. Colonic lesions are seen radiographically to consist of segmental ulceration,
inflammatory strictures, or hypertrophic lesions resembling polyps.[416] The granulomas can
occur anywhere from mucosa to serosa. Microscopically, these granulomas are discrete, white to
tan, and usually have necrosis, epithelioid cells, Langhans giant cells, and lymphocytes, albeit in
small quantities, along with acid-fast bacilli.
A presumptive diagnosis of mycobacteriosis for definitional criteria for a diagnosis of
AIDS may be made as follows:[392]
Microscopy of a specimen from stool or normally sterile body fluids or tissue from a site
other than lungs, skin, or cervical or hilar lymph nodes that shows acid-fast bacilli of a species
not identified by culture.

CYTOMEGALOVIRUS.-- Cytomegalovirus (CMV) is capable of infecting all parts of
the gastrointestinal tract, but the most common clinical manifestation is colitis. At least 20% of
patients with AIDS have gastrointestinal involvement with CMV. Clinically, there may be
diarrhea, fever, abdominal pain, hematochezia, weight loss, or anorexia.[418] Odynophagia
would suggest esophageal involvement.[487] There is no typical grossly identifiable pattern of
involvement. Gross lesions are often not present, but anything from mucosal erythema to small
mucosal ulcers to plaques may occur.[487]
Gastrointestinal perforation is an uncommon complication of CMV infection with AIDS,
but the most common cause for it is CMV infection. Patients can present with severe abdominal
pain, nausea, vomiting, fever, and leukocytosis. An abdominal radiograph will demonstrate
pneumoperitoneum. The most common locations for perforation are the ascending and
transverse colon, distal ileum, and appendix.[487,490] CMV can cause painful anorectal
ulcerations.[689]
A wide range of radiologic findings occur with gastrointestinal CMV infection. There
may be single or multiple large superficial esophageal ulcerations. Small bowel wall thickening
with thickened, irregular mucosal folds can be seen. Extensive ulceration with involvement of
the muscularis can lead to the appearance of a “CMV pseudotumor” ranging in size from a small
nodule to a large mass that can mimic a neoplastic lesion of Kaposi’s sarcoma or non-Hodgkin
lymphoma, though the inflammation associated with CMV typically leads to the finding of
infiltrative changes in adjacent mesenteric adipose tissue by computed tomographic scan.[416]
Cytomegalovirus may be diagnosed by endoscopic biopsy in which the characteristic
large cells with prominent homogenously staining violet intranuclear inclusion bodies (Cowdry
type A) are seen--most often in mucosal epithelial cells and occasionally in submucosal
endothelial cells. Cells with inclusions are often widely scattered and not numerous, and atypical