Pilocytic astrocytoma of the thalamus.
This 11-year-old male with papilledema presented with a 2-week history of headaches and intermittent nausea, vomiting, and diplopia. A. Unenhanced CT shows a cystic mass of the left thalamus, with a solid mural nodule. There is obstructive hydrocephalus. Peritumoral edema produces hypoattenuation in the left basal ganglia and adjacent white matter. B. A coronal FLAIR MR image shows peritumoral and periventricular edema. The mural nodule is slightly hyperintense. C. There is intense contrast enhancement of the mural nodule on this T1-weighted image obtained with IV gadolinium.