25 year old with prior bilateral ventricular shunting complained short-term memory

T1-weighted image (Image 1) reveals a homogeneously hyperintense oval unilocular mass of the anterior superior third ventricle at the foramen of monro. The ventricles are decompressed, with left frontal and right parietal ventricular shunts in place.

The axial T2-weighted image (Image 2) again demonstrates small ventricles after bilateral shunting. The mass is centeredat the foramen of monro and is homogeneous and markedly hypointense to both CSF and brain parenchyma. No other lesions are apparent

• Dx = Colloid (neuroepithelial) cyst of the third ventricle
• Colloid cysts are uncommon benign cyst of the anterior superior third ventricle, which are thought to arise from embryologic tissues of paraphysis, ependyma, or choroid plexus. These lesions typically present in young adults in the 2nd to 5th decade with complaints referable to acute or chronic hydrocephalus. Other symptoms include atacia, memory disturbances, and gait disorders. The cyst contents include secretory and breakdown products of the epithelial lining tissue, including hemorrhage, lipid (cholestrol), hemosiderin, and CSF
• On T1-weighted MR images, these cysts vary widely from hypo- to hyperintense in comparison to normal brain. Although they may be bright on T2-weighted images, moderate to marked hypointensity is common and has been attributed to avery short T1 relaxation time or to magnetic susceptibility effect from paramagnetic substances in the cyst. On noncontrast MR, these lesions occasionaly are indistinguishable by intensity from neoplasia; however, the absence of enhancement, classic location, and relative hypointensity on T2-weighted studies should suggest this diagnosis. Treatment is variable, including ventricular shunting alone, stereotactic cyst drainage, or surgical resection