Well-differentiated papillary mesothelioma of the peritoneum: a diagnostic dilemma on fine-needle aspiration cytology.

OBJECTIVES: Well-differentiated papillary mesothelioma of the peritoneum (WDPMP) is an uncommon subtype of epithelioid mesothelioma. Usually, WDPMP has a benign course, while a few patients have multiple recurrence and malignant transformation on long-term follow-up. The histology of WDPMP has been well studied compared with the cytology. Although accurate diagnosis is based only on histology and immunohistochemical stains, knowledge of the cytologic features of WDPMP in context with clinical and radiologic features is essential to predict a preoperative diagnosis and guide proper management, after excluding reactive mesothelial hyperplasia, malignant mesothelioma, and serous neoplasms of the ovaries and peritoneum. Surgical excision gives a favorable outcome. METHODS: We describe a case of 28-year-old woman who sought treatment for chronic lower abdominal pain, dysuria, and dyspareunia. RESULTS: Radiologic findings suggested multiple metastatic peritoneal deposits. Ultrasound-guided fine-needle aspiration cytology showed many papillae, tubulopapillary and spheroid groups, monolayered pavement-like sheets, and many dispersed cells. Papillae showed many layers of round to ovoid cells, with minimal atypia. Atypical mitoses and necrosis were not found. A cytologic diagnosis of WDPMP was suggested. After complete resection of all the tumor nodules, histopathology and immunohistochemical findings were compatible with WDPMP. On follow-up, she developed tumor recurrence at 9 months and was managed successfully with adjuvant chemotherapy. CONCLUSIONS: This article highlights the cytologic features of WDPMP with relevant review of the literature and differential diagnosis.