Specific Imaging Findings

Neurocutaneous melanosis (NCM) appears to involve the brain in specific locations; most commonly, melanocytic lesions are detected in the anterior temporal lobe (amygdala) and cerebellum, followed by the pons and medulla oblongata. Round or oval shaped lesions are best seen on T1-weighted images as areas of high signal intensity (due to melanin). The lesions are T2 iso- or hypointense and do not enhance with contrast. The T1 hyperintensity is more conspicuous within the first months of life, before the myelination appears complete on T1-weighted images. In patients with leptomeningeal involvement FLAIR images show sulcal/leptomeningeal hyperintensity and enhancement of the thickened leptomeninges is seen on post-contrast images, especially prominent along the basal cistern, tentorium, brainstem, inferior vermis and folia of the cerebellar hemispheres. NCM lesions are slightly hyperdense on CT; very high density may suggest associated hemorrhage. Echogenic foci may be seen on neonatal head ultrasound exam.

Pertinent Clinical Information

NCM typically presents early in childhood. Neurological manifestations of NCM are most commonly related to increased intracranial pressure, communicating hydrocephalus (due to the leptomeningeal melanocytic tumors) and epilepsy. Cranial nerve palsies are frequently associated. The risk for NCM is high in children with large congenital melanocytic nevi, in particular those over the trunk and neck with multiple satellite lesions. The criteria for diagnosing NCM are: (a) large or numerous pigmented nevi in association with leptomeningeal melanosis, (b) no evidence of malignant transformation of the cutaneous lesions, and (c) no malignant melanoma in other organs.