62 year old women comes to GP due to intermittent vaginal bleeding occurring in past 3 months. Her last menses was 5 years ago. She is sexually active with one monogamous partner and denies takign any prescription or OTC meds. Endometrial biopsy shows endometrial hyperplasia; no evidence of malignancy. Pelvic US shows solid, 4 cm, left ovarian mass. She undergoes resection of mass. Gross examination reveals an encapsulated tumor with yellow cut surface; no evidence of necrosis. Histologic examination reveals tumor cells with dark nuclei, scan cytoplasm, arranged in a microfollicular pattern. Immuno histochemical stain is positive for inhibin. 1. What is likely diagnosis and what features suggest that?

The development of the reproductive system begins with the formation of undifferentiated gonads and the paired mesonephric and paramesonephric ducts.