Giant congenital melanocytic nevi: The significance of neurocutaneous melanosis in neurologically asymptomatic children

Patients with a giant congenital melanocytic nevus can develop melanotic tu mors characterized by central nervous system involvement, termed leptomenin geal melanocytosis or neurocutaneous melanosis. Although symptomatic neuroc utaneous melanosis is rare, we previously reported distinct magnetic resona nce (MR) findings of T1 shortening, strongly suggestive of neurocutaneous m elanosis, in 30 percent (6 of 20) of children with giant congenital melanoc ytic nevi who presented initially without neurological symptoms. The purpos e of this study was to determine the incidence of neurocutaneous melanosis in high-risk patients and its long-term clinical significance. Magnetic resonance imaging was recommended for all 46 patients with "at-ris k" giant congenital melanocytic nevi involving the skin overlying the dorsa l spine or scalp. The clinical histories and follow-up of these patients we re evaluated by retrospective chart review. Forty-two underwent MR imaging of the brain and 11 underwent additional MR scanning of the spinal cord. Ab normalities were identified in 14 of 43 MR studies, and 23 percent (n = 10) had T1 shortening indicative of melanotic rests within the brain or mening es. None had associated masses or leptomeningeal thickening. The most commo n areas of involvement in these 10 included the amygdala (n = 8), cerebellu m (n = 5), and pens (n = 3). In the group of 11 patients with spinal MR sca ns, a tethered spinal cord was demonstrated in one. Additional abnormalitie s were detected by MR scanning, including a middle cranial fossa arachnoid cyst, a Chiari type I malformation, and a crescentic enhancement that subse quently resolved. Clinical follow-up averaging 5 years (range, 2 to 8 years ) revealed that only one of the 46 patients evaluated developed neurologica l symptoms, manifested as developmental delay, hypotonia, and questionable seizures but no other signs of neurocutaneous melanosis. No patient has dev eloped a cutaneous or central nervous system melanoma. Magnetic resonance f indings of neurocutaneous melanosis are relatively common, even in asymptom atic children with giant congenital melanocytic nevi. Although these findin gs suggest an increased lifetime risk of central nervous system melanoma, t hey do not signify the eventual development of symptomatic neurocutaneous m elanosis during childhood.