Intracranial malignant melanotic nerve sheath tumor: illustrative case.

Background: Melanotic schwannoma accounts for 1% of all nerve sheath tumors. These tumors were considered benign, but recent studies have shown their malignant propensity. They pose a diagnostic challenge given the rarity of the tumor.

Observations: The authors report a case of a 42-year-old woman who presented with headaches and a history of frequent falls for the past year. Brain MRI revealed a lesion in the posterior fossa, effacing the median aperture and cisterna magna, which was hyperintense on T1-weighted imaging and isointense on T2-weighted imaging, with significant blooming on susceptibility-weighted imaging. The patient underwent a midline suboccipital craniotomy and gross-total resection of the tumor. Histopathological examination revealed a malignant melanotic nerve sheath tumor (MMNST) with psammoma bodies and necrosis, indicating a poor prognosis.

Lessons: Melanotic schwannomas have a malignant propensity despite their benign morphology. Immunohistochemical analysis helps confirm the diagnosis of melanotic schwannoma. This is the 21st documented case of an intracranial MMNST, and, given the rarity of the tumor, there is scope for further research and studies on the role of radiotherapy in the management of these tumors. https://thejns.org/doi/10.3171/CASE24473.