Neurocutaneous Melanosis

At a glance

Rare skin (nevi) and meningeal pigmentation with a high risk of cutaneous or neural malignant degeneration.

Incidence

Around 100 cases have been described.

History

First described by Bohemian pathologist Carl von Rokitansky in 1861.

Genetic inheritance

Sporadic. It is caused by somatic mutation in the NRAS gene on chromosome 1p13.

Pathophysiology

Probably due to dysplasia of the neuroectodermal melanocyte precursor cells, leading to the proliferation of melanin producing cells in the skin and leptomeninges.

Diagnosis

At birth, large pigmented nevi, usually on the trunk, buttocks, or perineum. Cerebral MRI should be done before age 4 months to detect central nervous system (CNS) involvement.

Clinical aspects

Large pigmented nevi, usually on the trunk, buttocks, or perineum. CNS function may be normal at birth, but MRI examination is necessary to exclude brain or spinal cord involvement. If the CNS is involved, thickening and pigmentation of the meninges with focal accumulation of melanotic cells or brain stem lesions are observed. Progressive pigmentation and thickening of the meninges lead to cerebral deterioration, increased intracranial pressure, mental retardation, seizures, hydrocephalus, cranial nerve palsies, and spinal cord compression.

Precautions before anesthesia

CNS involvement (especially presence of increased intracranial pressure, brain stem lesions) should be excluded by MRI and/or eye fundus examination. If neuraxial blockade is foreseen for postoperative pain management spinal cord involvement should be excluded. In case of excision surgery, large blood loss should be foreseen.

Anesthetic considerations

In the presence of hydrocephalus, usual precautions to prevent any increase in intracranial pressure must be provided. If a spinal or epidural block is performed, the needle should not be inserted through a pigmented lesion to avoid skin coring and possible perimedullar implantation of melanocytes.

Pharmacological implications

As for any neonatal anesthesia. Patients may require repeated general anesthesia or deep sedation for dressing changes. Patients with seizure activity should have medication optimized prior to surgery or receive intraoperative intravenous supplementation.

Other condition to be considered

• Giant Neonatal Nevus without CNS Involvement: Sporadic; seems to be more frequent in Asian populations; early excision or laser therapy is performed by many medicosurgical teams for fear of malignant transformation.

References