In toto resection of a rare intradural extramedullary cavernous malformation on the S1 nerve root: illustrative case.

backgroundCavernous malformations (CMs) are vascular malformations that usually occur in the brain and occasionally in the spine. Most CMs are sporadic, but they can also be caused by heterozygous cerebral cavernous malformation (CCM) gene mutations. This case describes an intradural extramedullary CM in a unique location, within a fascicle of the S1 nerve root. This tumor was found to have a CCM2 mutation. An operative video demonstrates the surgical procedure used to remove this S1 intradural extramedullary CM. OBSERVATIONS: A 61-year-old male with an intradural extramedullary CM, located within a fascicle of the S1 nerve root, presented with pain and neurological symptoms. Additional imaging revealed two CCMs. The S1 CM was removed in toto. Subsequently, genetic screening revealed a CCM2 mutation. LESSONS: Given the rarity of a radicular CM, diagnosis can be challenging. CMs should be considered in patients with radicular pain and corresponding nerve root thickening. When a CM is suspected, imaging of the complete neuraxis should be performed. If multiple CMs are found, genetic screening is indicated. Complete resection of the CM yields good clinical results. The operative video in this case might help surgeons encountering this rare pathology to prepare for surgery. https://thejns.org/doi/10.3171/CASE24270.