CYTOLOGY OF GASTROINTESTINAL HISTOPLASMOSIS - A REPORT OF 2 CASES WITH DIFFERENTIAL-DIAGNOSIS AND DIAGNOSTIC PITFALLS

BACKGROUND: Gastrointestinal (GI) histoplasmosis is a rare manifestati on of Histoplasma capsulatum (HC) infection. There are no reports of i ts cytologic diagnosis in the literature. CASES: A search of cytology and surgical pathology files of the Methodist Hospital uncovered two c ases of GI histoplasmosis and histiocytes within cytologic specimens. Papanicolaou-stained endoscopic brushings of an obstructing, apple-cor e, right colonic mass in a 58-year-old, heterosexual male revealed num erous vacuolated single cells interpreted as suspicious for signet rin g cell carcinoma. The resected colon showed granulomatous inflammation with numerous histiocytes containing pale, oval yeasts of HC. The pat ient was subsequently found to be human immunodeficiency (HIV) positiv e; this was his first manifestation of the acquired immunodeficiency s yndrome. The second patient was a 69-year-old, HIV-negative male with a fungating anal mass suspicious for squamous cell carcinoma. Direct s mears showed oval histiocytes with intracellular yeasts of HC. CONCLUS ION: Accurate diagnosis is crucial to patient management and therapy. Careful attention to the nuclear and cytoplasmic details of histiocyte s and histiocytelike cells is important to avoid interpretive errors. Diagnostic pitfalls include signet ring cell adenocarcinoma, lymphoma, melanoma, goblet cell carcinoid, malakoplakia and such infections as mycobacteria, Entamoeba histolytica and Calymmatobacterium granulomati s. Ancillary studies, such as microbiologic cultures and immunohistoch emical and histochemical staining, can be performed in the appropriate clinical setting.