Answer: Sertoli-Leydig cell tumor

Histology: This tumor contains a network of tubules and cysts, into which are many small papillae with prominent hyalinized cores. The papillae are lined by stratified epithelial cells. In scattered foci there are cords and ribbons of immature sex cord-stromal cells with some features of tubule formation.

Discussion: Sertoli-Leydig cell tumors (SLCT) have been divided into six subtypes: well differentiated, intermediately differentiated, poorly differentiated, with heterologous elements, retiform, and mixed. Approximately 15% of SLCT are composed partially, or in some cases entirely, of tubular structures arranged in a pattern resembling that of the rete testis. The average age of patients with SLCT is 25 years, although tumors with a retiform pattern are more commonly seen in patients during the first decade than any other subtype. At laparotomy, most SLCT are unilateral and stage I. The rare tumors that present at a higher stage have a poor prognosis, with a mortality rate of 100% in one series of cases. There is also evidence that the presence of a retiform pattern has an adverse effect on prognosis. In contrast to granulosa cell tumors, which can recur many years after primary resection, SLCT typically recur relatively early. Although the treatment of SLCT depends on the age of the patient and the stage of the tumor, radiation and chemotherapy have been of benefit in some cases. Because of the characteristic papillary pattern and cellular stratification seen in retiform SLCT, a misdiagnosis of papillary serous carcinoma is occasionally made. However, the young age of the patient (12 years in this case), the association with virilization, and the presence of other more recognizable histologic patterns of SLCT are helpful clues in the diagnosis. The presence of epithelial and mesenchymal elements in some retiform SLCT can also cause confusion with a malignant mixed mesodermal tumor. Extensive histologic sampling of difficult tumors can help to exclude both of these latter diagnoses. The most common misdiagnosis in retiform SLCT is yolk sac tumor since both tumors occur in young women and both can demonstrate papillae within cystic spaces. Symptoms of androgenization, however, which can be seen in about 25% of cases of SLCT, are rare in cases of yolk sac tumor. Immunoperoxidase staining for alpha-fetoprotein in yolk sac tumor can also facilitate the diagnosis.