Fine-needle aspiration of a well-differentiated papillary mesothelioma in the inguinal hernia sac: A case report and review of literature

Well‐differentiated papillary mesothelioma (WDPM) is an uncommon subtype of epithelioid mesothelioma. In contrast to malignant epithelioid mesothelioma, WDPM has a low malignant potential and an indolent clinical course. WDPM may be difficult to diagnose and differentiate from benign reactive mesothelial cells and other malignant neoplasm on cytology specimens due to the presence of papillary or tubulopapillary clusters of tumor cells. We report a case of a 63‐year‐old Asian male with a slowly growing left inguinal hernia mass for several years and a concurrent 8 cm mass in the peritoneal wall. The cytology of ultrasound‐guided fine‐needle aspiration (FNA) of the left inguinal hernia and peritoneal masse reveal cellular specimens with numerous individual and tubulopapillary clusters of epithelioid mesothelial cells in a background of scant hyalinized material. Tumor cells show minimal cytological atypia. The differential diagnoses are broad and include reactive mesothelial cells, WDPM, and other malignant neoplasm. The follow‐up surgical resection of masses reveals features of WDMP. It is important to recognize this entity in the differential diagnosis, because the clinical management of WDPM is quite different from that of malignant neoplasm. On the basis of the published data in the literature, it suggests that in male patients, the WDPM occurs predominantly in pleural cavity of older men in their 50s, and about half of the patients have history of asbestos exposure. However, the data is limited and insufficient for a definitive conclusion. Diagn. Cytopathol. 2009. © 2009 Wiley‐Liss, Inc.