Cytomorphology of unusual infectious entities in the Pap test

Rare entities in the Pap test, including neoplastic and non-neoplastic conditions, pose challenges due to their infrequent occurrence in the daily practice of cytology. Furthermore, these conditions give rise to important diagnostic pitfalls. Infections such as tuberculosis cervicitis may be erroneously diagnosed as carcinoma, whereas others, such as schistosomiasis, are associated with squamous cell carcinoma. These cases include granuloma inguinale (donovanosis), tuberculosis, coccidioidomycosis, schistosomiasis, taeniasis, and molluscum contagiosum diagnosed in Pap tests. Granuloma inguinale shows histiocytes that contain intracytoplasmic bacteria (Donovan bodies). Tuberculosis is characterized by necrotizing granulomatous inflammation with Langhans-multinucleated giant cells. Coccidioidomycosis may show large intact or ruptured fungal spherules associated with endospores. Schistosoma haematobium is diagnosed by finding characteristic ova with a terminal spine. Molluscum contagiosum is characterized by the appearance of squamous cells with molluscum bodies. This article reviews the cytomorphology of selected rare infections and focuses on their cytomorphology, differential diagnosis, and role of ancillary diagnostic studies.