Colloid cyst

Colloid cyst. This non-contrast CT shows an incidental finding: a small hyperdense focus anterior to the third ventricle (arrow), with typical appearances of a colloid cyst. Although benign and usually incidental, these cysts can cause headaches, hydrocephalus and, rarely, sudden death. Characteristically, colloid cysts are high density on non-contrast CT. On MRI, they are unusual in that they typically return high signal on T1-weighted and low signal on T2-weighted sequences (the opposite of most pathological processes).