Meningeal melanocytoma

Meningeal melanocytomas are rare benign dural tumours that are derived from leptomeningeal melanocytes. They can occur anywhere along the neuraxis, but are most commonly found in the region of the foramen magnum, the posterior fossa, Meckel’s cave, or adjacent to cranial nerve nuclei 3.

Within the spine, melanocytomas present as intradural masses, and may be intradural extramedullary or rarely intramedullary. They are most commonly found in the upper cervical region, as melanocytes are most concentrated at this location 3.

Peak presentation is in the fourth and fifth decades. Occurrence in children is very rare 1.

Clinical presentation relates to tumour location and size. Spinal meningeal melanocytomas typically present with progressive pain, weakness and sensory deficits. Patients rarely present with subarachnoid haemorrhage.

Macroscopically, meningeal melanocytomas are circumscribed pigmented tumours. On light microscopy, there are spindle, fusiform, epitheloid or polygonal cells. The cells have eosinophilic cytoplasm with variable content of melanin pigment. Mitotic figures are rare or absent and necrosis and haemorrhage are generally not seen 1. These features help in differentiating melanocytomas from metastatic or primary melanomas of the central nervous system. Electron microscopic and immunoperoxidase staining allow for differentiation between melanocytoma and melanotic meningioma.

The preoperative diagnosis of meningeal melanocytoma is often difficult, as the clinical and neuroradiological features of the tumour are non-specific 2.

CT

Well-defined, isodense to hyperdense, homogenous, contrast enhancing lesion 1.

MRI

The MRI appearance of meningeal melanocytomas is variable, depending on the amount of melanin content present.

Signal characteristics include:

  • T1: isointense or hyperintense
  • T2: isointense or hypointense
  • T1 C+ (Gd): heterogenous enhancement
  • T2* GRE: may show blooming of low signal

Although classified as benign, meningeal melanocytomas may behave aggressively and a limited number may transform to malignant melanomas. Complete excision is the treatment of choice, however, this often not possible as intra-operative haemorrhage may be severe. Furthermore, local recurrence has been reported even after gross total removal 1. Due to the risk of tumour recurrence even after complete excision, adjuvant radiation therapy is advised in cases of both complete and incomplete resection 2.

Imaging differential considerations include:

In the spine, in addition to the lesions above, consider: 


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Article Information

rID: 20439
Synonyms or Alternate Spellings:
  • Meningeal melanocytomas
  • Spinal melanocytomas

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