MR of cellular blue nevus.

A 9-year-old boy had had a large nevus of the scalp since birth. When he was 3 years old, the nevus was excised. The histologic diagnosis was cellular blue nevus. Two years later a follow-up CT scan showed a high-density mass in the base of right middle cranial fossa (Fig . 1). Coronal CT scan showed an extracranial extension of the tumor through the right petrosal bone. Partial removal of the intracranial tumor was performed via a subtemporal approach. The temporal muscle, periosteum , dura mater, and the surface of the cerebral cortex were black, and a local extension of the scalp nevus to the CNS was confirmed. Three years after the surgery, MR examinations were performed with a 0.22-T scanner.