Appendageal tumors and tumor-like lesions of the testis and paratestis: a 32-year experience at a single institution.

The testicular hilum and paratestis contain several embryologically diverse anatomic structures, including the spermatic cord, tunica vaginalis, epididymis, rete testis, and several other embryonic remnants. Several benign and malignant lesions arise from these morphologically distinct structures, and owing to their proximity, it is challenging to classify and subsequently stage these tumors. Herein, we conducted a retrospective review of the paratesticular appendageal and rete testis tumors and tumor-like lesions diagnosed at our department from 1985 to 2016. Soft-tissue lesions/tumors were excluded. A total of 146 paratesticular appendageal and rete testis tumors and tumor-like lesions were identified. Most were benign (n = 107; 73%). Adenomatoid tumor (26%) was the most common benign tumor, followed by different types of cysts (19%), mesothelial hyperplasia (18%), serous cystadenoma (5.5%), and rete testis adenoma (4%). Malignant lesions comprised 23% of the cases, with mesothelioma the most common (15%), followed by adenocarcinoma of the rete testis (4%), serous cystadenocarcinoma (2%), and papillary and clear cell adenocarcinoma of the epididymis (2%). Finally, serous borderline tumors and melanotic neuroectodermal tumor (retinal anlage tumors) comprised the remaining 4% of cases. In conclusion, a wide range of benign and malignant lesions can arise from the paratesticular region. Awareness of these lesions and their histologic spectrum is crucial to avoid diagnostic pitfalls and to allow pathologists to establish a correct diagnosis and subsequent treatment plan.