Specific Imaging Findings

Pineal cysts are common and generally less than 15 mm in greatest dimension. When larger, they may compress the tectal plate and aqueduct resulting in hydrocephalus. Pineal cysts usually follow the signal intensity of CSF on T1- and T2-weighted images, occasionally having higher T1 signal. On FLAIR images they are usually brighter than the CSF. The contents are homogenous and follow the CSF on diffusion imaging. Their capsule is thin, less than 2mm in thickness and devoid of nodularity. Cysts may contain internal septations which are also thin. The details of their capsule are more evident with high-resolution volumetric acquisitions and at 3.0 T than at 1.5 T. After contrast administration, the capsule may show linear but never nodular enhancement. The veins around it enhance and may be confused with their capsule. Because they do not have a blood–brain barrier, on delayed post-contrast images they may show fluid levels or enhance in a near-complete fashion, making them difficult to differentiate from solid lesions. When they bleed (pineal apoplexy) they show varying signal intensities corresponding to the age of the blood. Enlarging or decreasing size of the pineal cysts are rare. Pineal cysts are less well seen on CT and a higher percentage of them appear falsely as solid masses.

Pertinent Clinical Information

Pineal cysts are usually incidental findings on imaging studies. It is estimated that up to 40% of the population has them and they are identified by MRI in 7–15% of adults. Pineal cysts usually have no clinical implications and remain asymptomatic for years. Symptomatic cysts vary in size from 7 to 45 mm and they may produce symptoms of headache, vertigo, visual and oculomotor disturbances, obstructive hydrocephalus, and Parinaud syndrome due to compression of the dorsal midbrain. If they acutely bleed internally, they may suddenly enlarge and produce all of these symptoms, which is known as pineal apoplexy.