Intracranial malignant melanotic nerve sheath tumor: illustrative case

Abstract

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.

Keywords: case report; intracranial; melanotic schwannoma; necrosis.

FIG. 1.

A: Axial contrast-enhanced T1-weighted MR image. B: Significant blooming is seen on the susceptibility-weighted image. C: Sagittal contrast-enhanced T1-weighted MR image showing contrast enhancement.

FIG. 2.

Left: Intraoperative photograph showing the tar-colored tumor (black arrow). Right: Intraoperative photograph obtained after gross-total excision of tumor.

FIG. 3.

Macroscopic appearance of the tumor.

FIG. 4.

A: The individual tumor cells are round to oval with epithelioid-like cells having abundant cytoplasm filled with grayish to grayish-brown granular pigment. B: Psammoma bodies are visible. C: Areas of calcification are seen. Hematoxylin and eosin, original magnification ×40.