Metastatic extra-axial medulloblastoma involving the trigeminal nerve: a rare prognostic entity with a comprehensive literature review.

Medulloblastomas (MB) are the most common malignant central nervous system tumors in children. They usually develop in the cerebellar vermis or the fourth ventricle, while in adults they typically originate from the paramedian region or the lateral cerebellar hemispheres. It's rare for MBs to originate outside the brain and spinal cord (extra-axial), such as in the skull, meninges, and nerves. Metastases of MB typically occur within the central nervous system, with metastases outside the nervous system (extra-neural) being uncommon at the time of diagnosis (1-2%), but can increase to 5-10% during advanced stages. Around 5-6% of MBs are associated with inherited cancer predisposition syndromes, with common genetic variants including PTCH1, SUFU, TP53, and SMO. This report describes the first pediatric patient harboring a CHEK2 germline variant of uncertain significance and developing a EA- MB localized at the trigeminal nerve and subsequent CNS and EN metastases.