Multicystic peritoneal mesothelioma: not always a benign disease.

Mesothelioma is a slow-growing insidious lesion of neoplastic aetiology arising from the pleural, peritoneal or pericardial mesothelium. It shows a predilection for the surfaces of the pelvic viscera and has a high rate of recurrence after excision. Cystic mesotheliomas are not associated with asbestos exposure. We report a case of cystic mesothelioma of the peritoneum encasing the ovary, which presented as a cystic adnexal mass. As highlighted in this case and other recent reports, a cystic mesothelioma should not be referred to as a benign cystic mesothelioma, as it has potential for locoregional invasion, as well as distant nodal and serosal metastases. This tumour should be treated with aggressive cytoreductive surgery and appropriate chemotherapy. We review the differential diagnosis of this rare entity and suggest guidelines for its differentiation.