Which rare congenital disorder is afflicting this three-year-old?

This three-year-old female with multiple congenital hairy nevi syndrome presents with speech difficulty and right hemiparesis. Which rare congenital disorder does she have, and what more common findings is this condition known to mimic? The first image shown is an axial T1 post-contrast with ill-defined meningeal enhancement (pink arrow), while images two and three are axial T1 pre- and post-contrast images from a few months later showing a mass (blue arrow). The fourth image is a sagittal T1 post-contrast with intrathecal enhancement (yellow arrows).

The answer is neurocutaneous melanosis. It is a rare congenital disorder causing dysplasia of neuroectodermal melanocyte precursor cells, which causes proliferation of melanin producing cells in the skin and leptomeninges. Benign overgrowth of melanocytic cells or development of malignant melanoma is often the cause of the death.

Differentials for the leptomeningeal melanocytosis and enhancement include subarachnoid hemorrhage on a non-contrast CT, or enhancing meningitis (malignant or infectious). Differentials for the melanocytic mass can include a meningioma, dermoid, or focal hemorrhage. Although rare, neurocutaneous melanosis should be considered when there is diffuse leptomeningeal enhancement with a rapidly-growing extra-axial mass.

Note: This case was shared by Dr. Neha Gowali, who was recently selected as a scholarship winner for ProScan’s NYC Neuro Case Review. Congratulations to Dr. Gowali.

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