Glioblastoma eroding through falx cerebri: a rarity or commonly seen? Illustrative case.

backgroundGlioblastoma, isocitrate dehydrogenase-wildtype CNS WHO grade 4 (formerly primary glioblastoma multiforme), is the most common and most malignant primary brain tumor. High-grade gliomas most commonly present as unifocal lesions; however, they invade the brain parenchyma in a diffuse manner, an attribute that renders successful resection difficult. Resection, wherein resection of more than 90% of the tumor mass must be achieved to improve outcomes, represents the first step in optimal treatment; therefore, surgical planning, approach, and technique are of utmost importance for successful treatment. OBSERVATIONS: In this paper, the authors present a rare case of a glioblastoma presenting as an atypical bilateral lesion with erosion through the falx cerebri. Morphologically, it was overtly distinct from a typical butterfly glioma. Initially, the authors believed this tumor to be a meningioma, or even a sarcoma, based on radiological morphology. Intraoperatively, destruction of the falx cerebri by the tumor, with spread to the contralateral hemisphere, was seen. LESSONS: To the best of the authors' knowledge, the erosion of the falx cerebri has not been previously described in glioblastoma in the literature, and this case highlights the importance of a thorough differential diagnosis and understanding its impact on surgical planning. https://thejns.org/doi/10.3171/CASE25410.