August 15, 2011
Asymptomatic six-month-old with multiple pigmented skin lesions noted at birth.
Neurocutaneous Melanosis
- Congenital dysplasia of neuroectodermal melanocyte precursor cells, with proliferation of melanin producing cells in the skin and leptomeninges. Parenchymal melanin is likely derived from melanocytes extending along perivascular spaces.
- The anterior temporal lobe, particularly the amygdala, is the most frequent location for parenchymal melanocytic accumulation. Other sites include the cerebellum and brainstem.
- Malignant degeneration of melanosis can occur and should be suspected if there is growth, mass effect, edema, nodular enhancement, or necrosis. Diffuse melanosis cannot be distinguished from metastatic melanoma. Both have a poor prognosis.
- Symptomatic neurocutaneous melanosis has a poor prognosis. Symptoms likely include increasing head circumference, seizures, vomiting, headache, cranial nerve palsy, irritability, and lethargy.
- Key Diagnostic Features: Normal MR does not exclude neurocutaneous melanosis. Foci of T1-hyperintensity will be seen at sites mentioned above. Diffuse leptomeningeal enhancement can be seen. Hydrocephalus can be seen with leptomeningeal disease.
- DDx: T1 hyperintense masses (lipoma, dermoid, melanoma); other causes of diffuse leptomeningeal enhancement
- Rx: Shunt for hydrocephalus, radiation therapy, chemotherapy and surgery
