Adult-onset medulloblastoma presenting in the setting of untreated spina bifida: illustrative case.

backgroundAdult-onset medulloblastoma in the setting of untreated spina bifida and Chiari type II malformation is exceptionally rare and has not been previously reported. The relationship between medulloblastoma and spina bifida remains poorly understood. OBSERVATIONS: An adult male with untreated spina bifida presented to the emergency department with headaches and was found to have a left cerebellar medulloblastoma and obstructive hydrocephalus. He underwent preoperative catheter-based angiography, which revealed inferior displacement of the venous sinuses. A suboccipital craniotomy for resection was performed, followed by radiation therapy and chemotherapy. Follow-up imaging at 3 months postoperatively demonstrated no evidence of residual tumor. LESSONS: Given the abnormal posterior fossa development in patients with spina bifida and Chiari type II malformation, posterior fossa surgery requires a thorough understanding of the patient's venous sinus anatomy to achieve a maximal safe resection and prevent venous sinus injury or thrombosis. While the role of CSF diversion in adults with untreated spina bifida is unknown, the authors opted to proceed with postresection ventriculoperitoneal shunt placement given the persistent mass effect on the fourth ventricle from peritumoral swelling. Additional studies are needed to establish a molecular and/or genetic relationship between medulloblastoma and spinal dysraphism. https://thejns.org/doi/10.3171/CASE24897.