Ovarian teratoma, also known medically as ovarian dermatomal cyst, is a germ cell tumor of the ovary. The cause of ovarian teratoma is unknown, as most occur before the oocyte matures and divides, presumably as a result of a failed first maturation division. The tumor contains three tissue components, ectodermal, mesodermal and endodermal, so the tumor will often contain ectodermal tissues such as hair, oil, skin, teeth and bone fragments, and may also contain mesodermal or endodermal tissues such as muscle, gastrointestinal and thyroid tissues. Because the center of ovarian teratoma is often on one side and higher, it is easy to be twisted.