Colloid Cyst

Colloid cysts are benign, congenital, mucus-containing, epithelium-lined cysts that almost always arise in the anterior third ventricle in the region of the foramina of Monro. They present in the third or fourth decade. The most common symptom is heaache.

CT findings in the characteristic location are usually enough for diagnosis. The attenuation on CT depends on hydration state, but approximately 2/3 demonstrate high attenuation. On T1-weighted images, the signal correlates with cholesterol concentration in the cyst. 2/3 are hyperintense on T1. On T1-weighted images, the signal correlates with water concentration in the cyst. The majority are isointense to brain on T2-weighted images. No suppression or restriction is seen on FLAIR and DWI, respectively. Usually no enhancement is seen.

Atypical Findings

Less than 1% can be seen in the lateral or 4th ventricles, cerebellum, or extraxial space. They are rarely low attenuation. Hemorrhage, enhancement, and calcification are also uncommon findings. About 25% have mixed attenuation/signal. Fluid-fluid levels are also uncommonly seen.