Neurocutaneous melanosis in 10-week-old girl. Axial T1-weighted MR image shows increased signal of neuromelanin within the amygdalae bilaterally, along the leptomeningeal surfaces of the brain stem and cerebellum and extending into the pons.
DDx: T1 Leptomeningeal hyperintensity- melanin (neurocutaneous melanosis, metastatic melanoma), blood (subarachnoid hemorrhage), fat (ruptured dermoid).
T2 Leptomeningeal hyperintensity- melanin (neurocutaneous melanosis, metastatic melanoma), hyperoxygenation (general anesthesia/sedation), infection/meningitis, metastatic disease (pineal/posterior fossa).
T1 enhancement- melanin (neurocutaneous melanosis, metastatic melanoma), infection/meningitis, metastatic disease (pineal/posterior fossa).
The current diagnostic criteria for neurocutaneous melanosis are (1) large (>20 cm) or multiple (>3) congenital nevi in association with meningeal melanosis or melanoma, (2) no evidence of meningeal melanoma except in patients in whom cutaneous lesions are histologically benign, and (3) no evidence of cutaneous melanoma except in patients in whom meningeal lesions are histologically benign.
http://imaging.consult.com/image/topic/dx/Brain%20and%20Spine?title=Neurocutaneous%20Melanosis&image=fig5&locator=gr5&pii=S1933-0332(08)70441-5
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