Diagnostic pitfalls of peritoneal washing cytology and the role of cell blocks in their diagnosis

Mesothelial cell hyperplasia, collagen balls, endometriosis, and endosalpingiosis are diagnostic pitfalls on peritoneal washing cytology in women who present with gynecologic lesions. Over an 8-month period, the peritoneal washings from 10 patients undergoing gynecologic surgery for presumed malignancy showed unusual cytologic findings, several of which posed diagnostic difficulties. The washings from four patients with ovarian carcinomas were cellular and contained clusters and strips of cells with cytologic atypia mimicking malignancy. Confirmation of their benign mesothelial origin was confirmed on immunohistochemistry utilizing cell block preparations. In two cases of endometrial endometrioid carcinoma, the washings contained several clusters of cells surrounding and/or admixed with a globular substance. Due to their similarity to endometrial cells, immunohistochemistry was performed on cell block preparations. The cells were positive for cytokeratin and negative for carcinoembryonic antigen and B72.3, confirming their mesothelial origin. In one case, clinically presumed to be a malignant mass, the washings contained tight clusters of cells with mild cytologic atypia admixed with hemosiderin-laden macrophages. In conjunction with the cell block findings, a diagnosis of endometriosis was made. Extensive endometriosis was found on the surgically resected specimen. In two cases, strips of ciliated epithelial cells resembling tubal epithelium were present on the cytologic and cell block preparations, consistent with endosalpingiosis. The peritoneal washings in one case contained several clusters and balls of atypical cells surrounding microcalcifications on cell block preparation. Since calcification within groups of cells in peritoneal washings always raised the possibility of malignancy, a serous carcinoma of the ovary, particularly of borderline malignancy, would have to be excluded. Fortunately, the resected specimen was free of tumor and showed calcified endosalpingiosis on the ovarian surface. Preparation of cell blocks from peritoneal washings is of value in the work-up and management of patients who present with cytologic mimickers of malignancy on fluid cytology.