Cyst vs. Gliosis on Mri Scan

I am wondering how radiologists and doctors can tell the difference between a harmless "cyst" of the brain, and something more serious like a brain lesion or gliosis from cns injury? Especially when they say that the cyst has most likely been present since birth and they typically do not cause symptoms. Do cysts appear difference in size or consistency compared to a glial scar or lesion....just curious as to how they know whether an abnormal structure on an mri can is serious or not.

[Ashwin Bhandari, MBBS]

Hi, Thanks for the query. A cyst will have a well defined border, in t1 image it will appear dark but in t2 white, a cyst if it is present for a long time it will tend to calcify. More importantly the history of the patient is very helpful. Have a nice day.