Cystoisospora belli Infection of the Gallbladder in Immunocompetent Patients: A Clinicopathologic Review of 18 Cases.

Cystoisospora belli, previously known as Isospora belli, is an obligate intracellular coccidian parasite that is most often associated with gastrointestinal disease in immunocompromised patients. In this study, we detail the clinicopathologic features of 18 cases of Cystoisospora infection affecting the gallbladder in immunocompetent individuals and compare them with a control group. Each case was reviewed for cholecystitis (none, acute, chronic), epithelial disarray, presence of intraepithelial lymphocytes (none, rare [≤5 per 20 epithelial cells], present [>5 per 20 epithelial cells]), architectural distortion, intramucosal eosinophilia, and mural thickening/serositis. The mean age of patients with Cystoisospora infection was 33 years and the male to female ratio 1:4.3. Cholecystectomy was performed for biliary dyskinesia (n=7), abdominal pain (n=7), suspected cholelithiasis (n=5), and cholecystitis (n=3). In 2 cases, Cystoisospora was found in donor gallbladders resected at the time of liver transplantation. Each case was characterized by eosinophilic, oval or banana-shaped intraepithelial parasites within perinuclear parasitophorous vacuoles. Most cases showed epithelial disarray and minimal intraepithelial lymphocytosis. Of the 11 cases with an average follow-up of 15 months, none had evidence of disease related to Cystoisospora infection within the biliary tract or elsewhere in the gastrointestinal tract. We present the largest series of gallbladder cystoisosporiasis in immunocompetent patients to date. Cystoisospora infection is underrecognized in the gallbladders of immunocompetent patients, in part due to the subtle findings in routine cholecystectomy specimens. On the basis of the clinical follow-up, gallbladder cystoisosporiasis in immunocompetent individuals appears to be a self-limited infection.