A teenage Chinese girl with intermittent limp and increasing headache was admitted to the hospital. She began to limp intermittently ten years earlier. A brain magnetic resonance imaging (MRI) showed multiple parenchymal lesions involving the pons, bilateral amygdala, and the left temporal pole (Figure 1A). She refused further investigations until a year earlier, when she developed mild headache. Magnetic resonance imaging showed minor focal enlargement of the lesions in the left temporal pole. One month before hospital admission, her headache aggravated and became intolerable. Enhanced MRI showed remarkable progression of the lesions in the left temporal lobe, involving the temporal pole and the parasylvian region, along with a newly developed mass in the third ventricle and obstructive hydrocephalus. The lesions in the pons and the right amygdala remained stable (Figure 1B). Spinal cord MRI was normal. There was no history of tumors elsewhere. Family history was unremarkable. Her consciousness was intact, but her memory and concentration were poor. Pupil reflection was normal. There were multiple congenital nevi distributed over the body, 2 of which on the legs were more than 5 cm in diameter, and another 3 on her back and face were more than 3 cm. There were no focal motor or sensory deficits. Muscle stretch reflexes were normal. The rest of the neurologic and systemic examination was unremarkable. Gene examinations showed a mutation in the N-ras-2 gene.