Neurosurgery notes/Tumours/Tumour syndrome/Neurocutaneous melanosis (NCM)

Neurocutaneous melanosis (NCM)

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Tumour syndrome

Definition

  • A rare, congenital, nonheritable phakomatosis
  • That usually presents before age 2 years
  • In which large or numerous congenital melanocytic nevi are associated with benign and/or malignant melanocytic tumors of the leptomeninges

Numbers

  • 60-70% develope symptoms before 5 yrs old

Pathogenesis

  • Neuroectodermal defect during morphogenesis involving melanoblasts of skin and pia mater originating from neural crest cells

Clinical features

  • 2/3 of patients have giant congenital melanocytic nevi:
    • Pigmented nevi that are large, hairy, or both.
    • The chances that nevi represents NCM is higher when the nevi are located on
      • Head,
      • Posterior neck, or
      • Paravertebral area
  • 1/3 have numerous lesions without a single giant lesion
  • 100% have large cutaneous melanocytic (pigmented) nevi located on the posterior torso
  • Neurologic manifestations: usually before age 2 years.
    • Signs of intracranial hypertension (lethargy, vomiting…), focal seizures, motor deficits or aphasia
  • Hydrocephalus: in almost 66%. Usually due to obstruction of CSF flow or reduced absorption as a result of thickened leptomeninges

Clinical diagnostic criteria

  • Unduly large or unusually numerous pigmented naevi in association with leptomeningeal melanosis or melanoma
  • No evidence of malignant change in any of the cutaneous lesions
  • No evidence of malignant melanoma in any organ apart from the meninges

Associated conditions

  • Other neurocutaneous syndromes
    • Sturge-Weber syndrome
    • von Recklinghausen’s neurofibromatosis (NF1)
  • Posterior fossa cystic malformations: e.g.
    • Dandy Walker malformation
      • Occurs in up to 10% of pts with DWS.
      • Have worse prognosis due to malignant transformation
  • Intraspinal lipoma and syringomyelia26

Diagnostic testing

  • MRI:
    • T1 and T2 signal shortening produced by melanin.
    • IV gadolinium may demonstrate enhancement of tumor-infiltrated meninges
  • Micro
    • CNS lesions shows leptomeningeal melanosis (benign) which develops from the melanocytes of the pia matter.
    • Melanoma (malignant) occurs in 40–62% of cases but distinction has little prognostic significance because of the poor outcome of the symptomatic NCM patient even in the absence of melanoma

Management

  • The benefit of resecting skin lesions is questionable in the presence of leptomeningeal lesions.
  • NCM appears refractory to radiation therapy and chemotherapy
  • Neurosurgical involvement is usually limited to:
    • Shunting for hydrocephalus
    • Palliative operative decompression if early in the course
    • Biopsy for tissue diagnosis in questionable cases

Prognosis

  • When neurological signs are present, prognosis is poor regardless of whether or not malignancy is present
  • >50% of patients die within 3 years after the first neurologic manifestation