Anaplastic oligodendroglioma: a case report with characteristic cytologic features, including minigemistocytes

Absolute criteria for grading oligodendrogliomas are somewhat poorly defined in contrast to those for grading astrocytic tumors, and cytologic features of anaplastic oligodendrogliomas have been poorly described.

A 63-year-old man presented with a toppling gait. Radiologic examination revealed a 7-cm mass with calcifications in the right frontal lobe. Intraoperative smears of the tumor showed hypercellular, loosely cohesive cell clusters and single cells with nuclear pleomorphism, numerous apoptotic cells and no discernible fibrillary processes. Many bland-looking round cells with cyanophilic cytoplasm and eccentrically located nuclei, so-called minigemistocytes, were intermingled among atypical cells. Cryostat sections showed cellular nests consisting of tumor cells with oval nuclei and clear cytoplasm. These cells were proliferating in the finely reticulated vascular stroma, and the tumor had an infiltrative margin with areas of focal necrosis and numerous calcifications. The diagnosis of anaplastic oligodendroglioma, World Health Organization grade 3, was made, and the results of fluorescence in situ hybridization (chromosome 1q deletion) supported the diagnosis.

Intraoperative diagnosis of anaplastic oligodendroglioma may not be easy but is possible with judicious consideration of several features: high cellularity, no fibrillary processes, nuclear atypia, pleomorphism, abundant apoptotic cells, occasional mitotic figures, coagulative necrosis, endothelial hyperplasia and characteristic conspicuous minigemistocytes.