In the World Health Organization Classification of Tumors of the Central Nervous System 2016 notable changes include the addition of brain invasion as a criterion for atypical meningioma 1).
Intracranial atypical meningiomas
Approximately 15-20% of meningiomas are atypical, meaning that the tumor cells do not appear typical or normal. Atypical meningiomas are neither malignant (cancerous) nor benign, but may become malignant.
Typical meningioma: Usually noninvasive, but histology is needed for definitive diagnosis.
Dural metastasis: Extracranial neoplasm is usually known (eg, neuroblastoma).
Lymphoma: Often lytic bone lesion with epidural and extracranial components.
Ewing sarcoma: Often osseous laminated periosteal reaction.
Only two prior cases of benign dendritic melanocytes colonizing a meningioma have been reported.
Dehghan Harati et al. add a third case, describe clinicopathologic features shared by the three, and elucidate the risk factors for this very rare phenomenon. A 29 year-old Hispanic woman presented with headache and hydrocephalus. MRI showed a lobulated enhancing pineal region mass measuring 41 mm in greatest dimension. Subtotal resection of the mass demonstrated an atypical meningioma, WHO grade II, and the patient subsequently underwent radiotherapy. She presented 4 years later with diplopia, and MRI showed an enhancing extra-axial mass measuring 47 mm in greatest dimension and centered on the tentorial incisura. Subtotal resection showed a brain-invasive atypical meningioma with melanocytic colonization. The previous two cases in the literature were atypical meningiomas, one of which was also brain invasive. Atypical meningiomas may be at particular risk for melanocytic colonization as they upregulate molecules known to be chemoattractants for melanocytes. We detected c-Kit expression in a minority of the melanocytes as well as stem cell factor and basic fibroblast growth factor in the meningioma cells, suggesting that mechanisms implicated in normal melanocyte migration may be involved. In some cases, brain invasion with disruption of the leptomeningeal barrier may also facilitate migration from the subarachnoid space into the tumor. Whether there is low-level proliferation of the dendritic melanocytes is unclear. Given that all three patients were non-Caucasian, meningiomas in persons and/or brain regions with increased dendritic melanocytes may predispose to colonization. The age range spanned from 6 years old to 70 years old. All three patients were female. The role of gender and estrogen in the pathogenesis of this entity remains to be clarified. Whether melanocytic colonization may also occur in the more common Grade I meningiomas awaits identification of additional cases 2).