First documented case of intracranial falcine malignant peripheral nerve sheath tumor: illustrative case

Background: The authors reported the first documented case of intracranial extraaxial nonneurofibromatosis type 1-related nontriton malignant peripheral nerve sheath tumor (MPNST) originating from the falx cerebri. Observations: A 34-year-old man with headache, short-term memory deficit, postural instability, and blurred vision presented with a large heterogenous contrast-enhanced intraventricular cystic lesion originating from the free margin of the falx cerebri. The patient received surgery using the right posterior interhemispheric approach. Gross total resection was performed, and the inferior border of the falx cerebri was resected. The postoperative course was uneventful. Histological examination revealed hypercellular foci of neoplastic spindle cells with hyperchromatic and wavy nuclei. Hence, a diagnosis of MPNST was made based on concomitant immunochemistry findings, including mouse double minute 2 homolog focal positivity and geographic loss of H3K27me3. The patient received adjuvant radiotherapy, and recurrence was not observed. Lessons: Intracranial MPNSTs are extremely rare tumors, typically originating from the cranial nerves in the posterior cranial fossa. An even rarer variant of these tumors, referred to as malignant intracerebral nerve sheath tumors, may directly arise from the brain parenchyma. The authors reported the first case of an intracranial MPNST originating from the dura mater of the falx cerebri, acting as an extraaxial lesion with prevalent expansion in the right ventricle.