Ovarian teratoma and granulosa cell tumor in two mares.

Simultaneous and successive occurrence of ovarian teratoma and granulosa cell tumor is reported in 2 mares. Simultaneous occurrence of the tumors may obscure clinical diagnosis. Whereas size, unilaterality, and the cystic nature of each may be similar, differentiating features include the potentially palpable presence of bone, cartilage, or teeth in teratoma, and the hormone-induced behavioral and reproductive effects of granulosa cell tumors. Thorough examination of surgical specimens may reveal the existence of a neoplastic process, previously obscured by the more obvious presence of another.