Answer: Sertoli cell tumor

Histology: The lesion consists of a fairly well circumscribed nodule within the testis, composed of tubules and cords of epithelium with focal myxoid features set in a dense sclerotic background.

Discussion: The presence of well formed tubules and glands raises the possibility of a teratoma. However, the tubules within a teratoma typically contain abundant apical cytoplasm resembling tubules seen in the GI or respiratory tract. No other components of a teratoma are identified within this specimen, making this an unlikely diagnosis. The presence of glands also raised the possibility of a metastatic adenocarcinoma. The most common metastatic adenocarcinoma of the testis is from the prostate. The presence of atrophic tubules, lack of significant cytologic atypia, and dense sclerotic background all are against a diagnosis of metastatic carcinoma. Areas of this lesion could resemble an adenomatoid tumor. Adenomatoid tumors are not typically found within the testis but are typically paratesticular in location. Although they may locally invade the testes minimally, only exceedingly rarely are they totally intratesticular. Other findings typically seen in adenomatoid tumors, such as signet ring-like cells, are also lacking in the current case. Focally, this lesion has a myxoid matrix, raising the possibility of yolk sac tumor. Yolk sac tumors have a multitude of histological pattern, including glandular variants. Typically, the glandular variants of yolk sac carcinoma do not show small atrophic tubules, as seen in the current case, but rather show well-formed glands often with subnuclear clear vacuoles. None of the other patterns of yolk sac tumor are present in the current case. The histological findings in this case are consistent with the remaining diagnosis, which is that of a Sertoli cell tumor. Whenever confronted with a gland-forming lesion within the testes, where the other lesions in the differential diagnosis have been ruled out, one is often left with the possibility of a Sertoli cell tumor. One can attempt to verify the diagnosis using stains for inhibin. However, in the current case, stains for inhibin were negative. Keratin stains are often positive in Sertoli cell tumors, yet that is not particularly helpful in the above differential diagnosis. Stains for alpha-feta protein and calretinin were negative in the current case, also helping to rule out yolk sac tumor and adenomatoid tumor. The distinction between benign and malignant Sertoli cell tumors is similar to that which has been proposed for Leydig cell tumors of the testis. The following features are more typically seen in malignant cell tumors, including: diameter greater or equal to 5 cm; necrosis; moderate to severe nuclear pleomorphism; vascular invasion; and greater than 5 mitoses per 10 high power field. In the current case, none of these findings were present, such that a benign clinical course would be expected.