Abstract

Malignant transformation of benign cystic teratomas of the ovary is rare, with an incidence rate of 1-3%. The most common malignancy associated with benign cystic teratoma of the ovary is squamous cell carcinoma, which represents 90% of malignant transformations, followed by adenocarcinoma and carcinoid. Primary malignant neuroectodermal tumor in a mature cystic teratoma is extremely rare and microscopically can be subclassified as differentiated, primitive, and anaplatic. We experienced a case of primitive neuroectodermal tumor (PNET) associated with mature cystic teratoma of the ovary in a 11-year-old girl. Grossly, the ovary was a unilocular cyst which contained sebum material and disclosed several large, yellow to gray-tan polypoid excresences attached to the inner cystic wall. Except a large, fish-flesh, soft mass, the other polypoid masses were covered with sebum and contained small pieces of cartilage and tooth, and microscopically represented as mature teratoma. The large, fish-flesh, soft mass disclosed sheets and lobules of closely packed small cells with thin fibrovascular septa, which frequently replacing and encroaching the mature cystic teratoma. The small tumor cells were uniform and made up of round to oval nuclei with coarse chromatin and prominent nucleoli, very similar to those of PNET of the central nervous system.

• Keywords: Primitive neuroectodermal tumor;Mature cystic teratoma;Malignant transformation;Ovary