Meningeal melanocytoma

Meningeal melanocytomas are rare benign primary melanocytic tumours of the CNS that are derived from leptomeningeal melanocytes. They can occur anywhere along the neuraxis but are most commonly found in the spinal canal near the foramen magnum, as well as the posterior fossa, Meckel’s cave, or adjacent to cranial nerve nuclei 3,4.

Peak presentation is in the fourth and fifth decades, although these tumours have been diagnosed in all age groups 1,4. Occurrence in children is very rare 1.

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

When these tumours are found in the trigeminal cave, then they are associated with a naevus of Ota, a benign dermal melanocytic nevus involving the ophthalmic (Va) and maxillary (Vb) divisions of the trigeminal nerve (CN V) 4,5

Meningeal melanocytomas are most common found in the cervical and thoracic regions (intrathecal-extramedullary). 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. Less commonly they occur in the intracranial compartment 4

Macroscopic appearance

Macroscopically, meningeal melanocytomas are circumscribed tumours. The degree of pigmentation is variable, ranging from black to non-pigmented 4

Microscopic appearance

On light microscopy, there are spindle, fusiform, epitheloid or polygonal cells without evidence of anaplasia. The cells have eosinophilic cytoplasm with a variable content of melanin pigment. Mitotic figures are rare or absent and necrosis and haemorrhage are generally not seen 1,4. These features help in differentiating melanocytomas from metastatic or primary melanomas of the central nervous system.

Immunophenotype

As is the case with other primary melanocytic tumours of the CNS, meningeal melanocytomas usually demonstrate the following immunohistochemical staining 4: 

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): heterogeneous 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 1-4. 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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