A biopsy or imaging
True pineal gland cysts are not brain tumors; rather, they are a completely benign cysts.
The large majority of pineal gland cysts do not enlarge much if at all. However, some do enlarge over time slowly. Even though pineal cysts are benign and usually harmless, they can mimic a tumor, they often need to be distinguished from other cystic tumors via biopsies or imaging
study (ie MRI
of the brain).