Most women with an adult granulosa cell tumor are diagnosed after age 30, with the average age being approximately 50 years. Menometrorrhagia and postmenopausal bleeding are common signs and reflect a prolonged exposure of the endometrium to estrogen. Grossly, adult granulosa cell tumors are large, multicystic, and often exceed 10 to 15 cm in diameter. Microscopic examination shows predominantly granulosa cells with pale, grooved, "coffee bean" nuclei. The characteristic microscopic feature is the Call-Exner body--a rosette arrangement of cells around an eosinophilic fluid space. Endodermal sinus tumors, or yolk sac tumors, are the third most common germ cell tumor. This is the most rapidly growing neoplasm that occurs at any site, and patients may present with an acute abdomen given they are friable, necrotic, and often hemorrhagic. These tumors are almost always bilateral and, on histologic section, resemble the primitive gut and liver; Schiller-Duval bodies, which show a single papilla lined by tumor cells with a central blood vessel, and the production of AFP are characteristic. Teratomas possess somatic cells from at least two germ cell layers (ectoderm, endoderm, and mesoderm). Variable degrees of differentiation allow for the subclassification of mature and immature forms. Mature teratoma consists of terminally differentiated tissues and can form cystic structures. Only about 2 to 3% of all Germ cell tumors show mature teratoma as the only histologic component, but teratoma is commonly present as an element of a mixed GCT. Ovarian fibroma can occur at any age but most often occur in the years before menopause. They range in size from incidental findings to greater than 20 cm. They are multinodular and whorled, and they are formed from bundles of collagen-producing spindle cells. Ref: Hoffman B.L., Schorge J.O., Schaffer J.I., Halvorson L.M., Bradshaw K.D., Cunningham F.G., Calver L.E. (2012). Chapter 36. Ovarian Germ Cell and Sex Cord-Stromal Tumors. In B.L. Hoffman, J.O. Schorge, J.I. Schaffer, L.M. Halvorson, K.D. Bradshaw, F.G. Cunningham, L.E. Calver (Eds), Williams Gynecology, 2e.