<unk> s belong to a class of tumors known as nonseminomatous germ cell tumor. All tumors of this class are the result of abnormal development of pluripotent cells: germ cells and embryonal cells.<unk> s of embryonic origin are congenital;<unk> s of germ cell origin may or may not be congenital. The kind of pluripotent cell appears to be unimportant, apart from constraining the location of the<unk>  in the body.<unk> s derived from germ cells occur in the testicle in men and ovaries in women.<unk> s derived from embryonic cells usually occur on the subject's midline: in the brain, elsewhere in the skull, in the nose, in the tongue, under the tongue, and in the neck (cervical<unk> , mediastinum, retroperitoneum, and attached to the coccyx.<unk> s may also occur elsewhere: very rarely in solid organs (most notably the heart and liver) and hollow organs (such as the stomach and bladder), and more commonly on the skull sutures.<unk>  rarely include more complicated body parts such as teeth, brain matter, eyes, or torso. Hypotheses of origin Concerning the origin of<unk> s, numerous hypotheses exist. These hypotheses are not to be confused with the unrelated hypothesis that fetus in fetu (see below) is not a<unk>  at all, but rather a parasitic twin.
Teratoma
Lipoma
Embryoma
Dermoid cyst
Gonadoblastoma
Spina bifida
Immature teratoma
Blastoma