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1.5 cm in diameter. They are often widely scattered, but they may also involve large areas of the
mucosal surface. Though the lesions are vascular, large hemorrhages are uncommon. The
lesions are usually asymptomatic, but occasional problems may include diarrhea, obstruction, or
protein losing enteropathy. Perforation is an uncommon complication. Radiographically, KS
most often produces multiple submucosal masses, with or without central ulceration that gives a
target-like lesion, though plaque-like lesions or small nodules may also be seen. The
microscopic appearance is similar to that seen elsewhere, but diagnosis can sometimes be
difficult due to: a submucosal distribution pattern, the microscopic similarity to granulation
tissue, or the small amount of tissue available from endoscopic biopsies.[416,667]

PROTOZOAL INFECTIONS.-- Gastrointestinal protozoal infections in patients with
AIDS are not rare. They can be asymptomatic, but the most common symptom is diarrhea.
They are transmitted via a fecal-oral route, typically from contaminated food or water containing
the infective spores (oocysts), from person to person. Infection from inhalation of spores has
also been postulated. In persons who remain relatively healthy, the diarrhea is usually self-
limited, but in the later stages of AIDS, particularly when the CD4 count is <100/µL, protozoal
infections are more frequent and patients can have protracted diarrhea, though death from
protozoal infections alone is not common.[487] Combination antiretroviral therapy, including a
protease inhibitor, has been shown to be effective in improving immune function to lessen the
effects of these pathogens.[672]
Cryptosporidium can produce enteritis with significant diarrhea in patients with AIDS.
Cryptosporidiosis can occur in both immunocompetent and immunocompromised hosts, but in
the former it is mainly a cause for self-limited diarrhea of 1 to 2 weeks duration in children. In
immunocompromised hosts cryptosporidiosis can be the cause for a life-long, protracted diarrhea
that is refractory to therapy. Cryptosporidiosis is a chronic infection in about half of affected
AIDS patients, while it is transient in about one fourth, and fulminant in less than 10%. It is
estimated to afflict 10 to 20% of patients with AIDS and diarrhea in the U.S., and half of such
patients in developing nations. Cryptosporidiosis produces a voluminous, watery diarrhea with 6
to 25 bowel movements per day with a maximum stool volume of 1 to 17 liters.[486] It is often
accompanied by abdominal cramps, low-grade fever, anorexia, electrolyte imbalance,
dehydration, and weight loss, though it rarely leads to death.[417,487] No effective treatment
has been developed. Cryptosporidium organisms may also be found in biliary tract, pancreas,
and lung.[486,487,662,673,674]
Radiographic features of cryptosporidiosis in the small intestine include thickened
mucosal folds when inflammation is present, or effacement of folds with villous atrophy. There
can also be blunting, fusion, or loss of villi. Increased fluid secretion can lead to dilution of
barium.[416]
Cryptosporidium does not usually produce grossly visible lesions such as erosions,
ulcers, or masses, though there may be mild erythema and granularity. Microscopically on small
intestinal biopsy samples, cryptosporidia are small 2 to 4 micron sized round organisms that
occur singly or in rows along the mucosal brush border from villi to crypts, sometimes
accompanied by acute inflammation and crypt abscesses. They are best diagnosed by
examination of stool specimens with acid fast stain under oil immersion.[401] Giemsa and PAS
stains may also demonstrate these organisms. On electron microscopy, the organisms appear
embedded in a cytoplasmic vacuole on the microvillus border.[486,667] Postmortem diagnosis