A case of myxoid variant of epithelioid mesothelioma of the peritoneum with signet ring cells: A diagnostic pitfall on fine needle aspirate cytology

The myxoid variant of epithelioid mesothelioma is a rare subtype of malignant mesothelioma. Peritoneal involvement by malignant mesothelioma is much less common than pleural involvement. We present a rare case of epithelioid mesothelioma of the peritoneum with extensive myxoid change in a 44-year-old man. The patient presented with lower abdominal pain; imaging studies revealed a pelvic mass. An ascitic fluid aspirate performed at an outside facility has been misinterpreted as a signet ring carcinoma associated with pseudomyxoma peritonei. Histologic examination of the laparoscopically obtained biopsy performed in our facility confirmed epithelioid mesothelioma with extensive areas of myxoid stroma and focal areas of classical epithelioid mesothelioma, proven by immunohistochemical studies. Although rare, the myxoid variant of mesothelioma should always be remembered and included in the differential diagnoses of myxoid lesions of the peritoneum, including pseudomyxoma peritonei. This is particularly important when dealing with a case of diffuse peritoneal-based pathology. We hope to add our case to increase knowledge and awareness of this rare entity and avoid diagnostic misinterpretation.