Primary Melanocytic Tumors of the Central Nervous System in Children: Imaging Features with Pathologic Correlation

Primary melanocytic tumors of the central nervous system are rare neoplasms arising from proliferation of multipotent melanin-containing neural crest cells found in the leptomeninges. This review describes the imaging appearance of the entire spectrum of primary melanocytic tumors of the brain and spine in the pediatric population, in correlation with histopathology, clinical features, and prognosis, using sample cases from our institution. These tumors are subclassified by the World Health Organization on the basis of disease distribution and pathologic aggressiveness into the following 4 subtypes: meningeal melanocytoma, meningeal melanoma, meningeal melanocytosis, and meningeal melanomatosis. They can occur in any age group, though the diffuse form of the disease is more prevalent in children and has an association with giant cutaneous melanocytic nevi. Imaging is characterized by hyperattenuation on CT and intrinsic T1 hyperintensity on MR imaging from the presence of melanin and/or hemorrhage. The focal forms usually manifest as duralbased hemorrhagic masses, and the diffuse forms demonstrate dural thickening and enhancement, with or without hydrocephalus. There is a predilection for the medial temporal lobes, posterior fossa, and upper cervical spine. The prognosis is often poor, with a high incidence of malignant transformation of benign disease. Learning Objective: To describe the imaging appearance of the spectrum of primary melanocytic tumors of the brain and spine in the pediatric population and to review the histopathology, clinical, and prognostic data available.