Cysts and epithelial proliferations of the testicular collecting system (including rete testis).

Neoplastic and non-neoplastic proliferations of the testicular collecting system may be a source of diagnostic difficulty as they are rarely encountered and may have an appearance that leads to confusion with lesions arising in adjacent structures. The rete testis and epididymis are the 2 sites that are most likely to give rise to this unusual group of lesions. This article principally, although not exclusively, deals with those lesions that produce an intrascrotal mass. These include benign acquired or developmental cysts such as cystic dysgenesis of the rete testis or acquired cystic transformation of the rete testis, non-neoplastic epithelial proliferations such as adenomatous hyperplasia of the rete testis or cribriform hyperplasia of the epididymis, and benign or malignant neoplasms. Rete testis cystadenoma, including the sertoliform variant, and papillary cystadenoma of the epididymis are examples of benign tumors of the testicular collecting system that must be considered, the latter is the more likely of the 2 to be encountered. Primary carcinoma of either the rete testis or the epididymis is a rare occurrence; these entities are considered in some detail to allow for their recognition and distinction from other tumors that may occur in this region. Our own experience with 18 unpublished cases of lesions of the rete is also present.