Papillary mesothelioma of the tunica vaginalis propria testis. Case report and ultrastructural study.

Ultrastructural features of a papillary mesothelioma arising in a hydrocele-sack are reported. The tumour cells presented numerous microvilli, desmosomes, basement membranes and abundant bundles of microfilaments, which all are hallmarks of mesotheliomas. The predominant cell type was the "clear epithelial cell", but transitional cells and degenerative forms (foamy cells) were also found. The morphology and differential diagnosis of mesothelial tumours arising in the tunica vaginalis propria testis are discussed.