 Surgery (by craniotomy, open brain surgery) may be offered based on the risks of treatment as determined by the Spetzler – Martin scale (grade I-V); this score is higher in larger lesions that are close to important brain structures and have deep venous drainage. High grade lesions (IV and V) have an unacceptably high risk and surgery is not typically offered in those cases. Radiosurgery (using targeted radiation therapy such as by a gamma knife) may be used if the lesion is small but close to vital structures. Finally, embolization may be used on small lesions that have only a single feeding vessel.
