These are usually benign tumours growing from the meninges (the outer covering of the brain) which irritate and compress the surface of the brain where they are situated. They are one of the more common tumours in the skull and tend to occur in certain defined areas. They are slow growing but may be already too big for Gamma-Knife Radiosurgery treatment at the time of presentation. These large tumours and those on the surface are usually removed by surgery. Stereotactic radiosurgery is of value as an adjunct to sub-total microsurgical removal or as a primary treatment where surgery is not suitable.
A good example (as shown) is a combined treatment for a meningioma invading the cavernous sinus. This means that the surgery to these lesions can be less aggressive, removing the outer portion and leaving the part in the sinus. This remnant can then be treated effectively with Gamma Knife radiosurgery.