Why is watching a small meningioma best? when is it big enough to take out? is one that is 12 mm small enough to watch or take out?

Active Surveillance.: 90% of meningiomas are benign. Most grow slowly. It does not make sense to go putting a hole in your head and potentially cause a whole host of problems to remove something that is not causing and may never cause a problem. In general, active surveillance is a good strategy. A tumor that is producing symptoms or growing needs to come out.