Colloid Cyst, 3rd Ventricle
86 y/o man presenting with dementia.
A well defined oval mass is seen in the anterior 3rd ventricle, appearing of lower density than brain on the T1-weighted images and showing high signal on the proton density and T2-weighted images. With Gadolinium, no significant enhancement is seen.
Third ventricular colloid cysts are gelatinous-filled cystic masses that commonly occur in the anterior third ventricle adjacent to the foramen of Monro. These may cause obstruction of the foramen. They are commonly bright on T1-weighted images and of lower signal on T2-weighted images, but the reverse pattern is not uncommon, as seen in this case. CSF flow artifacts may simulate a cyst in this region.