Selected other problematic testicular and paratesticular lesions: rete testis neoplasms and pseudotumors, mesothelial lesions and secondary tumors.

The proximity and, in some instances, communication between several structures in the testis and paratestis (rete testis, epididymis, mesothelium, vestigial epithelium and paratesticular soft tissue) result in a plethora of interesting tumors and tumor-like lesions that together pose a formidable diagnostic challenge both because of their morphologic overlap and rarity. The occasional spread of tumors primarily at other sites to this region adds to the potential problem encountered. This review provides an overview of the pathology of nonmesenchymal paratesticular neoplasms and pseudotumors with a focus on the approach to tubulopapillary neoplasms for which diagnostic considerations may include carcinoma of the rete testis, malignant mesothelioma, ovarian-type epithelial tumors, epididymal carcinoma and metastatic carcinomas. The cornerstone of accurate characterization of these lesions is still a comprehensive, traditional clinicopathologic approach, clinical history (of another primary), gross examination (location) and routine light microscopy, but judicious incorporation of contemporary immunohistochemical markers may aid or in some instances be crucial in resolving the problems encountered.