MR of neurocutaneous melanosis

To describe the MR findings of neurocutaneous melanosis in the brain and correlate these with the known pathology and proposed embryologic basis of this disorder.

The brain (seven patients) and spine (three patients) MR scans of seven patients with neurocutaneous melanosis were retrospectively reviewed. In two patients, findings were confirmed at surgery. The pattern of central nervous system involvement was also correlated with known pathologic studies regarding frequency and location of melanotic deposits.

Five patients had regions of T1 shortening in the cerebellum; three of these also had T2 shortening. Five patients had regions of T1 shortening in the anterior temporal lobes. Other areas of involvement included the pia mater over the cerebellum (two patients), pons (one patient), medulla (one patient), and left parietal lobe (one patient). Only two lesions showed enhancement, edema, or necrosis; both were proved malignant melanomas at biopsy. No pial enhancement was detected.

Neurocutaneous melanosis appears to involve the brain in specific locations that can be detected on MR imaging. Knowledge of these locations can aid in differentiating metastases, secondary to malignant degeneration of the large cutaneous nevi, from melanotic deposits that are a part of the disease. Identification of malignant degeneration of the melanotic deposits is difficult; at present, it depends on the identification of growth, edema, or necrosis of the deposits.