Staged radiosurgery for extra-large cerebral arteriovenous malformations: method, implementation, and results.
OBJECTIVE
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.


METHODS
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).


RESULTS
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.


CONCLUSIONS
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.
Chung
Wen-Yuh
WY
Department of Neurosurgery, Taipei Veterans General Hospital, Taipei, Taiwan. wychung@vghtpe.gov.tw
Shiau
Cheng-Ying
CY
Wu
Hsiu-Mei
HM
Liu
Kang-Du
KD
Guo
Wan-Yuo
WY
Wang
Ling-Wei
LW
Pan
David Hung-Chi
DH
D000328:Adult; D002533:Cerebral Angiography; D015331:Cohort Studies; D005260:Female; D006801:Humans; D002538:Intracranial Arteriovenous Malformations / Q000000981:diagnostic imaging / Q000473:pathology / Q000601:surgery*; D008279:Magnetic Resonance Imaging; D008297:Male; D016634:Radiosurgery / Q000009:adverse effects / Q000379:methods*; D011879:Radiotherapy Dosage; D012189:Retrospective Studies; D018570:Risk Assessment; D016896:Treatment Outcome; D055815:Young Adult