Reversible edema after radiosurgery for arteriovenous malformations (AVMs): Inflow and outflow imbalance

We examine the remodeling of arterial feeders and draining veins following Stereotactic Radiosurgery (SRS) and explore their relationship with radiation-induced edema using retrospective data from 50 patients with cerebral AVMs treated with CyberKnife between 2010 and 2023 at a single center. Univariate analyses were performed. 46% of patients developed post-SRS edema. Patients with edema had larger AVM volumes (4.5 vs. 2.1 cm³; p < 0.01) and showed greater reduction in the diameter of their main draining vein (33% vs. 13%; p < 0.01) and accessory draining vein (24.5% vs. 6%; p < 0.01). Those without edema had a larger reduction in the diameter of the main feeder artery (15% vs. 8%; p = 0.03). Patients with edema showed higher change in resistance to outflow in the main draining vein (406% vs. 71%; p < 0.01) and second largest vein (192% vs. 27%; p < 0.01), while those without edema showed higher resistance to inflow in the arterial feeder (95% vs. 38%; p = 0.03). There were no differences in radiation dosing (p = 0.97), obliteration rates (p = 0.35), or functional outcomes (p = 0.61) at follow-up. Post-SRS edema in AVMs is associated with higher resistance to outflow seen in a disproportionated greater reduction in the size of draining veins compared to arterial feeders.