Benign Rete Testis Mimicking as a Small Cell Carcinoma in a Hydrocele Specimen – A Rare Finding in a Veteran Patient and a Diagnostic Pitfall

Abstract

Abstract Introduction/Objective Hydrocele specimens are one of the most common and routine urological specimens sent to pathology with mostly a benign outcome. Microscopic examination usually reveals loose connective tissue, mesothelial lining and possibly chronic inflammation, squamous metaplasia in long standing cases. Methods We present here a case of a veteran with rare finding of small, blue clusters of hyperchromatic cells in a hydrocele specimen mimicking small cell carcinoma. Results An elderly African American patient presented to the urology with a symptomatic hydrocele for elective removal. His review of systems preoperatively and intraoperative finding was otherwise unremarkable. Gross examination of the specimen showed a fibro-membranous tissue without any nodules or lesions. Microscopic examination showed fibromuscular tissue with scattered, detached clusters of small, blue, hyperchromatic cells with high nucleo-cytoplasmic ratio, nuclear molding without prominent nucleoli. Morphologically these features were suspicious for malignancy such as small cell carcinoma. However, no apparent mitotic figures or necrosis was noted. On immunohistochemical stains, these cells showed expression of CD 56, however proliferation rate on Ki67 was very low (0–1%). Conclusion Non-neoplastic proliferations are rare in testis and para-testicular structures. Rete testis is an anastomosing network of delicate channels located in the testicular hilum lined by flattened cuboidal to columnar epithelium with numerous microvilli. In a long-standing hydrocele specimen, the cells of rete testis may get sloughed off and form aggregates of small, blue hyperchromatic cells, morphologically mimicking as small cell carcinoma. However, on close examination, these cells in cluster were “streaming”, no necrosis, atypical mitotic figures or apoptotic cells were noted. Also, it has been well known that normal rete testis cells are positive for CD 56. Thus, low ki67 proliferation rate, CD 56 positivity and absence of necrosis or mitotic figures were consistent with sloughed rete testis cells. This is a very rare finding in a routine hydrocelectomy specimens, not only highlighting the importance of thoroughly grossing the specimens; at the same time, knowledge of this benign mimicker is important to avoid erroneous diagnosis and management.