Glioneuronal tumor with neuropil-like islands.

Mixed glioneuronal neoplasms are relatively uncommon tumors in the central nervous system. Recently, an unusual glioneuronal tumor arising in adults marked histologically by neuropil-like islands was described. We present a similar case arising in a 23-year-old woman who presented with headaches and seizures and on imaging studies was noted to have a frontal-temporal lobe mass. The patient underwent partial resection of the tumor, which histologically resembled anaplastic astrocytoma, and received a course of radiation therapy and chemotherapy. Increasing seizure frequency and expanding size on neuroimaging prompted a re-excision of the tumor. The second resection was marked by islands of tissue resembling gray matter with slightly atypical neuronal and glial cells situated in the white matter. These islands stained positively with synaptophysin and did not stain with glial fibrillary acid protein. Mild vascular proliferation and moderate nuclear pleomorphism also characterized the tumor. Areas of necrosis were not noted. A MIB-1 labeling index of 18.1% was noted. P53 immunoreactivity was observed in approximately 40% of tumor cell nuclei. This lesion is felt to represent a clinically aggressive glioneuronal neoplasm with an unusual and distinctive histologic phenotype. HUM PATHOL 31:1435-1438.