Multicystic mesothelioma caused by endometriosis: 2 case reports and review of the literature.

Multicystic mesothelioma was described as a benign neoplasm in most reports. But, whether it is neoplastic or reactive is still controversial. Although multicystic mesothelioma is often accompanied by endometriosis, histologic findings of the lesion with endometriosis have not been well documented. In this report, 2 cases of multicystic mesothelioma with endometriosis were studied histologically. The first lesion consisted of multiple cysts having thin walls lined with single-layered cuboidal mesothelia, and in the cystic walls, small foci of endometriosis were found. The second lesion was next to the endometriotic cysts in the pelvic space. These histologic findings suggest that endometriosis greatly contributes to the origin of the lesions. In addition, from the review of the literature, cystic mesothelioma was divided into 2 categories, that is, neoplastic or non-neoplastic lesions. Differentiation of both disorders might be possible by the following: size of the lesion, macroscopic and microscopic solid proliferation, features of adenomatoid tumor, and common mesothelioma-like histology. In conclusion, multicystic mesothelioma accompanied by endometriosis is thought to be a secondary non-neoplastic lesion induced by adhesion or inflammation rather than a neoplasm.