BACKGROUND The presence of intracranial collision tumors, histologically distinct tumors occurring in anatomical proximity, is quite rare. Herein, the authors describe the sentinel case of a contiguous collision tumor combination consisting of glioblastoma multiforme and intraventricular subependymoma. OBSERVATIONS A 67-year-old male presented with several months of progressive fatigue superimposed on more recently noted word-finding difficulty, slight left-sided weakness, and episodic confusion. He was found to have a large right frontal mass abutting the right lateral ventricle with an additional nodular focus of enhancement within the right frontal horn. The patient underwent an awake right frontal craniotomy for gross-total resection of the tumor, noted to be of two distinct histological identities. LESSONS Although exceptionally rare, primary glial neoplasms of various histologies can be encountered simultaneously during resection, as in this case of co-occurring glioblastoma of the right frontal lobe and right frontal horn intraventricular subependymoma. Close attention to tumoral locations and the gross appearance of specimens during resection can prime the operative neurosurgeon for success in contributing to accurate diagnoses through sending separate pathological specimens for histological analysis when qualitatively different tissue is suspected.
