Glioneuronal Tumor With Features of Ganglioglioma and Neurocytoma Arising in the Fourth Ventricle: A Report of 2 Unusual Cases and a Review of Infratentorial Gangliogliomas.

Infratentorial glioneuronal neoplasms are overall quite rare and are more commonly low-grade with surgical excision usually being curative. Multiple distinct histologic entities have been described including rosette-forming glioneuronal tumor, papillary glioneuronal tumor, neurocytoma, dysplastic gangliocytoma of the cerebellum (Lhermitte-Duclos disease), cerebellar liponeurocytoma, and ganglioglioma. While each of these entities has distinct findings, in some instances a tumor may demonstrate overlapping histologic features with mixed components. Herein, we report 2 unusual adult cases of a fourth ventricular glioneuronal tumor with features of ganglioglioma and neurocytoma, with one coming from a surgical resection and one found incidentally at autopsy. To the best of our knowledge, this specific histologic combination has not previously been described. As such, the clinical significance is unknown although in both cases the neoplasms were circumscribed and appeared to be low grade. The presence of the gangliogliomatous component was of particular interest since these are extremely rare occurrences in the fourth ventricle and we provide a comprehensive review of infratentorial gangliogliomas.