The effectiveness and safety of radiosurgery for small- to medium-sized cerebral arteriovenous malformations (AVMs) have been well established. However, the management for large cerebral AVMs remains a great challenge to neurosurgeons. In the past 5 years the authors performed preplanned staged radiosurgery to treat extra-large cerebral AVMs.
An extra-large cerebral AVM is defined as one with nidus volume > 40 ml. The nidus volume of cerebral AVM is measured from the dose plan—that is, as being the volume contained within the best-fit prescription isodose. From January 2003 to December 2007, the authors treated 6 patients with extra-large AVMs by preplanned staged GKS. Staged radiosurgery is implemented by rigid transformation with translation and rotation of coordinates between 2 stages. The average radiation-targeted volume was 60 ml (range 47–72 ml). The presenting symptoms were seizure in 4 patients and a bleeding episode in 2. One patient had undergone a previous craniotomy and evacuation of hematoma. The mean interval between the 2 radiosurgical sessions was 6.9 months (range 4.5–9.1 months). The prescribed marginal dose given to the nidus volume in each stage ranged from 16 to 18.6 Gy. The expected marginal dose of total nidus was 17–19 Gy. Regular follow-up MR imaging was performed every 6 months. The mean follow-up period was 28 months (range 12–54 months).
Most of the patients exhibited clinical improvement: relief of headache and reduced frequency of seizure attack. All patients had significant regression of nidus observed on MR imaging follow-up. Two patients had angiogram-confirmed complete obliteration of the nidus 45 and 60 months after the second-stage radiosurgical session. One patient experienced minor bleeding 8 months after the second-stage radiosurgery with mild headache. She had satisfactory recovery without clinical neurological deficit after conservative treatment.
These preliminary results indicate that staged radiosurgery is a practical strategy to treat patients with extra-large cerebral AVMs. It takes longer to obliterate the AVMs. The observed high signal T2 changes after the radiosurgery appeared clinically insignificant in 6 patients followed up for an average of 28 months. Longer follow-up is necessary to confirm its long-term safety.