Answer: D. Granulosa cell tumor

Histology: At low magnification, the lesion is well circumscribed and is separated by eosinophilic collagen bundles. At higher magnification, there are irregular nests of cells having round-ovoid nuclei and evenly dispersed chromatin without readily visible nucleoli. Many cells have nuclear grooves. Mitotic figures are infrequent. Occasional follicular structures containing watery eosinophilic secretions in the lumina are seen surrounded by cells with rounded nuclei.

Discussion: The tumor at low magnification has the typical appearance of a benign sex-cord stromal tumor of the testis. These tumors characteristically are well circumscribed and have bands of bright eosinophilic collagen dissecting the tumor. The key diagnostic criteria in this case resides in the nuclear appearance. In contrast to the last case, the nuclei in this case are not neuroendocrine. Instead of rounded nuclei with salt and pepper nuclei seen in a carcinoid tumor, the nuclei in this case are angulated with more dense chromatin. Sertoli cell tumor nuclei resemble those seen in normal Sertoli cells consisting of slightly ovoid uniform nuclei with delicate homogeneous chromatin and a single centrally located small but distinct nucleolus. In the current case, the nuclei lack these features and intead many have nuclear grooves typical of a granulosa cell tumor. Another unique feature diagnostic of a granulosa cell tumor is the presence of Call-Exner bodies described above with follicles containing eosinophilic secretions. Sertoli cell tumors often have ill defined lumina trying to recapitulate seminiferous tubules but not the well defined tubules with secretions of Call-Exner bodies. It is important to distinguish a benign Sertoli cell tumor from a granulosa cell tumor, as patients with the former can be told that they are cured following orchiectomy, whereas granulosa cell tumors as in the ovary are more unpredictable in their behavior. Although the majority of testicular granulosa cell tumors behave in a benign fashion, a few have not despite the lack of overt malignant histological features. Immunohistochemistry is not helpful to distinguish amongst sex-cord stromal tumors, as they stain similarly, The best and most commonly used markers that label these tumors are inhibin and steroid factor 1 (SF1).