Primary peritoneal ependymoma.

Extra-axial ependymomas are exceedingly rare neuroectodermal tumors that arise outside the central nervous system. The majority behave in a benign clinical fashion. In this case, an elderly woman developed an intraperitoneal ependymoma that after surgical excision recurred twice over a period of twenty four years. At each presentation, the tumor demonstrated identical histologic appearances with prominent rosettes as well as perivascular pseudorosettes. Immunohistochemistry showed strong positivity for glial fibrilary acidic protein, estrogen receptors, CAM 5.2 and CD99 with weak staining for pankeratin. Staining was negative for epithelial membrane antigen (EMA) and S-100. Ultrastructurally, the neoplasm showed neuroectodermal features, including filamentous cytoplasm and abundant intercellular bridges. The patient had no lesions in the central nervous system or the para-spinal region, suggesting that this tumor arose spontaneously within the abdominal cavity.