I posted a thread earlier about having headaches and weakness for the past couple of months. Initially they did a CT and MRI that showed a small nodule (6mm) in my brain. A month later, I had another MRI (this time with contrast) and the radiologist didn't note this spot, but it is still there. I went to the neurologist today and asked her about it and it is definitely still there (and looks more pronounced than on the MRI from a month earlier). My neurologist seemed dismissive of it and said it looked like a cyst, but not to worry about it because it's in the left frontal lobe ("an area of your brain that doesn't really do anything anyway") and is still small. She compared it to an MRI I had 9 months ago and there is absolutely no evidence of a cyst on it at that point.
My neurologist didn't seem to care about it, but should you do anything about a brain cyst that relatively suddenly appears? She said we could do another MRI in a year or so to make sure it wasn't growing ("to make me feel better"). What causes brain cysts (that aren't congenital)? Should I have any monitoring of it or treatment for it? (I do have a history of a tumour in my right orbital bone that was on the lining of my brain when I was a toddler, so being concerned about something in my brain does not seem to be entirely without reason).