Papillary mesothelioma of ovary

A case of primary papillary mesothelioma of the ovary is reported and its microscopic and ultrastructural features described. This tumour was an incidental surgical finding and was accompanied by multiple, partially cystic, peritoneal lesions with similar microscopic features. The histological pattern was predominantly papillary with well-differentiated mesothelial cells and a prominent stromal infiltrate that included large numbers of lymphocytes and lipid-filled macrophages. A comparison is made with adenomatoid tumours and with other tumours of ovarian epithelium and it is suggested that this tumour may represent the benign counterpart of one form of clear cell carcinoma of the ovary. The presence of multiple peritoneal lesions may indicate limited malignant potential comparable to some other papillary epithelial neoplasms of the ovary.