Neurocutaneous melanosis

Last revised by Rohit Sharma on 11 Oct 2022

Neurocutaneous melanosis or neurocutaneous melanomatosis, is a rare sporadic phakomatosis characterized by multiple congenital cutaneous nevi and meningeal melanocytosis/meningeal melanomatosis

Neurocutaneous melanosis tends to be diagnosed in the first few years of life with no gender predilection reported 5,7. The condition is most frequently reported in Caucasians 7

The disease is characterized by multiple melanotic nevi in the skin. Approximately two-thirds of patients have a giant nevus covering the back, known as a "bathing trunk" congenital nevus 7.

The diagnosis is often made when the child presents with hydrocephalus due to meningeal melanocytosis/meningeal melanomatosis (a.k.a. diffuse melanosis) 5. Occasionally a delayed presentation occurs towards the end of the second decade, in which case neuropsychiatric presentation is more common 7.

Diagnostic features have been proposed 2:

  1. unduly large or unusually numerous pigmented nevi in association with leptomeningeal melanosis or melanoma
  2. no evidence of malignant change in any of the cutaneous lesions
  3. no evidence of malignant melanoma in any organ apart from the meninges

It is believed that neurocutaneous melanosis is the result of congenital dysplasia of melanoblasts (melanocyte precursors) which are of neural crest cell origin 1,4,7. These are located in the leptomeninges, optic globes, inner ear, sinonasal cavity, and skin 1,4

For leptomeningeal imaging features, please refer to meningeal melanocytosis.

In addition to or instead of leptomeningeal involvement, parenchymal changes are seen in some individuals characterized by T1 signal hyperintensity involving the mesial temporal lobes (particularly the amygdala), ventral pons and medulla, cerebellum, and inferior frontal lobes 6,7. It is believed this is due to melanocytes tracking along perivascular spaces 7

Malignant degradation of CNS melanosis is suggested by interval increase in size, central necrosis and hemorrhage, perilesional edema, and local mass effect, but none are characteristic 8

Prognosis in symptomatic cases is extremely poor, even in the absence of malignant transformations, particularly when associated with a Dandy-Walker malformation 7. Hydrocephalus is the most common complication. Involvement of the cord also may result in myelopathy, syringomyelia, and arachnoiditis

Malignant transformation of cutaneous nevi is variably reported from 2-13% 4

Malignant transformation of CNS melanosis occurs very frequently, in up to 50% 5.

ADVERTISEMENT: Supporters see fewer/no ads