Image #1: T1W sag images show high signal round mass in the
anterior, superior third ventricle obstructing the Foramen of Monro
and causing hydrocephalus.
Image #2: T2W axial images show dark signal round mass in the
Image #3,4: T1W post gad axial and coronal images show high
signal mass in third ventricle without obvious enhancement.
This is the classic appearance for a colloid cyst. These lesions
usually occur in adults and is rare in children. They are almost
always located in the anterior, superior third ventricle and are
very rare anywhere else in the brain.
Patients present because the mass can cause intermittent
hydrocephalus causing headaches and vertigo. On CT, two thirds are
hyperdense, and one third are isodense to brain. Usually does not
enhance but sometimes can demonstrate rim enhancement.
On MR, the lesions have variable signal characterisitics but
most often demonstrate high signal on T1 and low signal on T2.
Diagnostic Neuroradiology, Osborn.