Gamma knife^® radiosurgical strategy for pediatric high-grade arteriovenous malformations: Advantages of staged radiosurgery prior to targeting nidus proximal to the drainer

Background: The management of high-grade (Spetzler-Martin grade 4-5) arterio-venous malformations (AVMs) still has many risks, and even the use of a multidisciplinary approach is commonly insufficient for a cure. In pediatric patients, Gamma Knife^® radiosurgery as a sole modality may result in radiation injury such as radiation necrosis or cyst formation, affecting their lives in the future. For these cases, 'staged radiosurgery' is preferred. We present our treatment cases and report the concept, achievements, advantages and possibilities for AVMs. Methods: First, we target nidus proximal to the draining vein, limiting volume up to 3.0 cm³ with 22 Gy as the peripheral dose. This radiation method enables to: (1) target only the real nidus, (2) lower the risk of radiation injury, (3) treat residual nidus just as in 'virgin cases', and (4) cause thrombosis naturally in residual nidus. It is more advantageous in pediatric AVMs because their radiation sensitivity is much higher. 25 pediatric AVMs (20.8% of all AVMs) have been treated in our institution since 2002. Among them, 4 were high-grade AVMs and followed at least 2 years (2-4 years). Results: Even though follow-up is still continuing, there has been no hemorrhage or radiation injury. Three AVMs disappeared spontaneously on image within 2 years and did not require second radiosurgery. Conclusion: Staged radiosurgery is a safe and effective treatment strategy for pediatric high-grade AVMs. Pediatric AVMs respond readily to radiosurgery compared to adults. More cases with a longer follow-up will establish this treatment concept as a defined strategy.