Sacrococcygeal Teratomas

derived from more than one of the embry onic germ layers. As proposed by Willis,' these neoplasms are composed of multiple tissues of kinds foreign to the parts in which they arise. Based on this definition, terato mas can be distinguished from mixed tu mors (like those of the salivary glands), embryomas and similar tumors (such as nephroblastomas and hepatoblastomas), and hamartomas (which are composed of a mixture of elements normally found in the site). The teratoma must contain tissue for eign to that anatomical site and tissue that cannot have resulted from metaplasia. In contrastto incompleteconjointtwins, which may mimic a teratoma,a truetera toma has a high degree of disorganization and may be inherently malignant or have the potential of malignant degeneration. Various theories of origin for teratomas include: parthenogenetic development of. germ cells within the gonads or in extra gonadal sites; nonparthenogenetic origin from “¿ wandering― germ cells left behind during the migration of embryonic germ cells from yolk sac to gonad: and origin