Diagnosis

Colloid Cyst

Findings

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 third ventricle.

Image #3,4: T1W post gad axial and coronal images show high signal mass in third ventricle without obvious enhancement.

Discussion

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.