Papillary glioneuronal tumor: a case report and review of the literature.

Papillary glioneuronal tumor is a recently described central nervous system neoplasm that almost always occurs adjacent to the lateral ventricle. We present a case of this rare entity, representing the 21st case of this lesion, which exhibits a mixed astrocytic and neuronal differentiation. This case was an incidental finding in a young woman who presented secondary to a traumatic injury to the left eye. Histologic evaluation after surgical removal showed a cystic tumor consisting of 2 distinct components: a unique pseudopapillary architecture admixed with foci of solid areas. The pseudopapillae were composed of thick hyalinized vessels enclosed by a single layer of glial fibrillary acid protein-positive astrocytes and variously sized synaptophysin-positive and chromogranin-negative neuronal cells in the interpapillary regions. Abundant Rosenthal fibers, foci of calcification, areas of hemosiderin deposition, gliosis, areas of vascular proliferation associated with piloid gliosis, and chronic inflammatory infiltrate were identified. The combination of cytologic benignity, lack of necrosis, and low proliferative index as evidenced by immunohistochemistry using antibody to Ki-67 confirmed the low malignant potential of this tumor. Knowledge and precise classification of this entity are important to avoid unnecessary use of chemo- and/or radiotherapy for treatment.