Fine needle aspiration cytology of well-differentiated papillary mesothelioma: A case report

Background: Well-differentiated papillary mesothelioma (WDPM) is an uncommon subtype of mesothelioma that typically occurs in the peritoneum of women without a history of asbestos exposure and usually follows an indolent clinical course. Fine needle aspiration (FNA) of this type of tumor has rarely been reported. Case: A 64-year-old woman with 11-year history of colon cancer and an adrenal nodule was found, on abdominal computed tomography, to have a mass in the right lobe of the liver. Aspirates of the mass were composed of abundant, tight, papillary groups, monolayered, pavementlike sheets; and scattered single cells with minimal atypia. The cell block showed a predominantly papillary growth pattern and a single layer of bland, cuboidal to flattened covering cells with stout, fibrovascular cores containing clusters of foamy histiocytes. Tumor cells in the focal tubulopapillary and solid areas were mingled with inflammatory cells and showed slightly more atypia than did the cells covering the papillae. The differential diagnoses were intrahepatic papillary neoplasm, including well-differentiated mesothelioma and metastatic low grade papillary serous carcinoma. At surgery the tumor was found to be a pedunculated peritoneal mass that arose from the posterior surface of the right lobe of the liver. The mesothelial origin of the tumor was confirmed by both immunoperoxidase study and electron microscopic examination, which demonstrated long, slender, branching microvilli. Conclusion: Familiarity with the cytomorphologic features and clinical presentation of WDPM, knowledge of the exact anatomic location and consideration of the appropriate differential diagnosis combined with ancillary studies are the keys to an accurate diagnosis.