= small nonneoplastic cyst of pineal gland

Incidence: 25–40% on autopsy; 4–23% on imaging

Age: any, predominantly 40–49 years; M <F

Origin:

1. developmental = persistence of ependymal-lined pineal diverticulum
2. degenerative = glial-lined secondary cavitation within area of gliosis

Path: uni- / multilocular cyst; inner layer = gliotic tissue, middle layer = pineal parenchymal tissue, outer layer = connective tissue; proteinaceous / hemorrhagic cyst fluid

• rarely cause of hydrocephalus (← compression / occlusion of aqueduct) with headache / visual change
• NEVER associated with Parinaud syndrome

Size: 2–15 mm, remaining stable over time; may be symptomatic if >15 mm

• round / oval thin-walled well-circumscribed cyst
• ± calcification

CT:

• normal-sized gland (80%), slightly >1 cm in 20%, can be >2 cm in size
• isodense to CSF in surrounding cistern (infrequently noted)

MR:

• isointense to CSF on T1WI; may have higher signal intensity than CSF ← high protein content
• slightly hyperintense to CSF on T2WI ← phase coherence in cyst but not in moving CSF
• signal not completely suppressed on FLAIR ← proteinaceous content
• typically incomplete enhancement of cyst wall ← fragmentation of pineal parenchyma as cyst enlarges
• appearance of a solid mass on delayed contrast images (contrast may diffuse from enhanced rim of residual pineal tissue into fluid center ← NO blood-brain barrier)
• slight impression on superior colliculi (sagittal image)

Prognosis: lack of growth over 9 years (in 75%); rarely “pineal apoplexy” = intracystic hemorrhage

Follow-up: for cysts ≥10 mm

DDx: cystic tumors (astrocytoma, pineocytoma, pineoblastoma)