Introduction: Due to the Spetzler-Martin grading scale’s composition, grade III AVMs are the most heterogeneous being comprised of four distinct lesion subtypes. We report our experience with radiosurgery for a large cohort of grade III AVMs.

Methods: From 1989 to 2009, all patients with Spetzler-Martin grade III treated with Gamma Knife radiosurgery at the University of Virginia were identified. After excluding patients with less than 2 years of radiologic follow-up except those with evidence of complete obliteration, 398 patients harboring grade III AVMs were analyzed. The most common presenting symptoms were hemorrhage (59%), seizure (20%), and headache (10%). The median AVM volume was 2.8 cc, and the median prescription dose was 20 Gy. The median radiologic and clinical follow-up intervals were 54 and 68 months, respectively.

Results: Complete AVM obliteration following radiosurgery was observed in 69% of grade III AVMs at a median time of 46 months. The obliteration rate was higher in ruptured AVMs than unruptured ones (P<0.001). Additionally, the obliteration rate for grade III AVMs with small size (<3 cm), deep venous drainage, and located in eloquent cortex was higher than for the other subtypes (P<0.001). Pre-radiosurgery AVM rupture (P=0.016), no pre-radiosurgery embolization (P=0.003), increased prescription dose (P<0.001), fewer isocenters (P=0.006) and single draining vein (P=0.018) were independent predictors of obliteration. The annual risk of post-radiosurgery hemorrhage during the latency period was 1.7%. Two patients (0.5%) died of hemorrhage during the radiosurgical latency period. The rates of symptomatic and permanent radiation-induced changes (RIC) were 12% and 4%, respectively. No pre-radiosurgery AVM rupture (P<0.001) and single draining vein (P<0.001) were independent predictors of RIC.

Conclusions: Radiosurgery for Spetzler-Martin grade III AVMs yields relatively high rates of obliteration with low a rate of adverse procedural events. Small and ruptured lesions are more likely to obliterate after radiosurgery than large and unruptured ones.

Patient Care: As a consequence of their heterogeneity, the management of grade III arteriovenous malformations is both difficult and controversial. Our retrospective analysis demonstrates that Gamma Knife radiosurgery affords a favorable risk to benefit profile for grade III AVMs, especially those which are ruptured or small.

Learning Objectives: By the conclusion of this session, participants should be able to 1) Describe the outcomes of Gamma Knife radiosurgery as a treatment approach for Spetzler-Martin grade III arteriovenous malformations, 2) Discuss, in small groups the patient, arteriovenous malformation and treatment characteristics which predict obliteration and radiation-induced changes following radiosurgery, and 3) Identify an effective treatment for grade III arteriovenous malformations.

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