Colloid cyst

51-year-old with an incidentally discovered colloid (paraphyseal) cyst. Sagittal (A) and coronal (B) T1-weighted MRIs show a small hyperintense lesion (arrows) in the roof of the third ventricle, just caudal to the pillars of the fornix. On a transverse axial T2-weighted image (C), the cyst is isointense to brain and therefore difficult to identify. On noncontrast CT (not shown), the cyst was hyperdense. Both density and signal intensity of colloid cysts reflect cholesterol, mucin, and water content.