Hari
Please elaborate, how large.
Apart from what Dr.Ashwini said, there are some centres do phased radiosurgery for slightly bigger AVM's. Half of the nidus is irradiated in one sitting and the other half is irradiated in next sitting 2-3 months later. There was a session in ASTRO this year on AVM's and some speaker from Pittsburgh said there is absolutely no role of hypofractionated SRT and they do phased SRS for some selected cases. I agree with Dr.Ashwini as by and large radiosurgery is a poor option in large AVM's.
There was also a hypothesis saying that larger the AVM's the lesser is the probability to bleed. The reason is turbulence in smaller AVM's is more. with multiple feeders, the turbulence may get distributed. So if the lesion is in non-eloquent area - surgery is choice, irrespective of age and grade of AVM. if the lesion is in eloquent area, observation can be an option.
Please comment on AOVM's (Angiographically occult) please, as in last one year I have seen 3 cases which were referred to me for SRS.