[Teratoma of the ovary. Clinical and pathological differences between mature and immature teratomas].

Teratomas are the most frequent germ cell tumors of the ovary. Two main groups can be distinguished: mature and immature teratomas. Mature teratomas are benign tumors, which are most often composed of derivatives of two or three germ cell layers. Only in rare cases is the transition into a malignant tumor observed (most often squamous cell carcinoma). In contrast, immature teratomas are malignant ovarian tumors. They contain immature tissue elements in addition to the mature components, most often consisting of immature neural tissue. Histologically, this tumor component can be identified as neurotubules or rosettes. The proportion of immature tissue elements defines the grade of immaturity. Four grades have been defined in to the WHO classification. Grade 0 represents a mature teratoma. With the exception of childhood cases, grade 2 and 3 immature teratomas are treated with chemotherapy. In childhood cases, foci of yolk sac tumor (YST) must be looked for, since this determines the prognosis. If a focus of YST is present, the patient is treated with chemotherapy. Both in cases of mature and immature teratoma, peritoneal implants can be found (gliomatosis peritonei), which are also graded. In cases of immature peritoneal implants, patients are also treated with chemotherapy. Gliomatosis peritonei is most likely derived from metaplasia of subperitoneal stem cells; it does not represent a metastatic disease of the ovarian teratoma.