A rounded lesion with intermediate T1 and high T2 signal is noted in the roof of the third ventricle, just behind the foramina of Monro. The choroidal veins (draining the choroid plexus of the lateral ventricle), and the thalamostriate veins (which join on each side to form the internal cerebral veins) are seen stretched over the lesion.
Lateral ventricles are distended well above that expected for this age.
Features are characteristic of a colloid cyst.