BACKGROUND Collision tumors (coexistence of histologically distinct intracranial neoplasms) are exceedingly rare in patients without genetic predisposition or prior cranial irradiation. Meningioma-glioma combinations are the most frequently reported, with 22 pathologically confirmed cases to date. While a few cases have undergone genetic analyses, methylation classifier analysis has not been previously performed. OBSERVATIONS A 71-year-old woman presented with cognitive decline and gait disturbance. Imaging revealed a superficial, intensely enhancing nodule with hyperostosis, adjacent multiple striated lesions, and a deep cystic lesion. The resected tumor was pathologically diagnosed as meningothelial meningioma with brain invasion. Additional resection was scheduled, but the residual tumor grew rapidly. Subsequent resection of the residual tumor revealed a collision tumor, composed of glioblastoma, IDH-wildtype, and meningothelial meningioma. Imaging patterns, including nodular and ring-like enhancing lesions with intervening hypoattenuated or multiple striated zones, correlated with histopathology. Methylation classifier analysis revealed the glioblastoma as glioblastoma, IDH-wildtype, mesenchymal type, and the meningioma as meningioma, subtype benign. LESSONS Collision tumors are difficult to diagnose preoperatively; prognosis is primarily determined by the glioma component. Meticulous review of neuroimages, intraoperative recognition of dual pathologies, multiple tissue sampling, and comprehensive molecular analyses are essential for accurate diagnosis, surgical planning, and postoperative management. https://thejns.org/doi/10.3171/CASE25952
Ueno et al. (Mon,) studied this question.