Background: Patients with giant or multiple congenital melanocytic nevi occasionally have leptomeningeal melanocytosis, also called neurocutaneous melanosis (NCM). Patients with symptomatic NCM usually have signs or symptoms of increased intracranial pressure and have a poor prognosis. Magnetic resonance (MR) imaging is sensitive in detecting melanin; several recent reports have described the MR findings in neurocutaneous melanosis.

Objective: The aim of this study is to review the brain MR findings and their potential significance in a group of neurologically asymptomatic children with giant congenital melanocyte nevi at risk for the development of NCM.

Methods: Retrospective review of patient charts and MR studies was performed.

Results: Nine of the 20 patients evaluated had MR abnormalities: six had focal areas of high signal on T₁-weighted images, strongly suggestive of melanosis, in one or multiple areas of the brain including the temporal lobes, cerebellum, pons, and medulla. One had a middle cranial fossa arachnoid cyst; another had a Chiari type I malformation of the brain. In one patient a crescentic enhancement over the right parietal region, probably from perinatal trauma, was absent on repeat MR 6 months later. In no case was thickening of the leptomeninges or spinal abnormalities noted.

Conclusions: NCM may be much more common than previously suspected in patients with giant congenital melanocytic nevi. The most common finding on MR appears to be T₁ shortening in the cerebellum, temporal lobes, pons, and medulla, rather than evidence of leptomeningeal thickening. These findings may have implications for management of patients with giant CMN.