Extra-ovarian mature teratoma arising from the posterior cul de sac

Teratomas are germ cell neoplasias consisting of tissue from the three laye rs of the developing embryo (ectoderm, mesoderm, and endoderm), These tumor s are most commonly found within the ovary; extra-ovarian mature teratomas in adults are considered to be rare. A 64-year-old woman, gravida 4 para 4, had an 8x7 cm solid pelvic mass posterior to the uterus by examination and radiologic studies. On exploratory laparotomy, an extra-ovarian mature ter atoma arising from the peritoneum in the posterior cul de sac was found. Th is is the first reported case of extra-ovarian mature teratoma arising from the peritoneum in the posterior cul de sac, Even though extra-ovarian tera tomas are rare in adults, they should be considered in the differential dia gnosis in a woman with a pelvic mass of unclear origin.