Prognostic value of nidus sphericity in brain AVMs treated with Gamma Knife Radiosurgery: a preliminary study

To evaluate the association of the three-dimensional (3D)-modelled sphericity index of brain arteriovenous malformation (AVM) with nidus obliteration rate and time following Gamma Knife^® Radiosurgery (GKRS), and to compare the predictive value of the AVM nidus sphericity index with previously established morphological predictors, such as AVM volume.

This institutional review board-approved retrospective study included 44 patients with cerebral AVMs who underwent single-session or hypofractionated GKRS between 2020 and 2023. Patients who received multimodal therapy, including prior endovascular embolization or microsurgical resection of the AVM nidus, were excluded. A minimum follow-up of 24 months was required for study inclusion. The primary endpoint was defined as complete angiographic obliteration following the initial GKRS, without any latent intracranial hemorrhage requiring hospitalization or surgical intervention. Pretreatment threshold-based semi-automatic segmentation of the AVM nidus was performed to obtain its volume and surface area, from which the sphericity index (Φ) was calculated.

Nineteen (43.2%) AVMs achieved obliteration at a mean of 35.7 ± 11.4 months, whereas 25 (56.8%) had residual nidus at 43.7 ± 13.4 months. Sphericity values were more compact and stable, whereas volume showed wide variability across the groups. The median volume of obliterated AVMs was 1.6 (3.9) cm³, and the median volume for AVMs with residual nidus was 4.9 (13.7) cm³ (P = 0.002). Median AVM sphericity was 0.53 (0.26) for obliterated AVMs and 0.32 (0.19) for AVMs with residual nidus (P = 0.003). Sphericity demonstrated fair discriminative performance, comparable to AVM volume (Φ cut-off: 0.41; sensitivity 79%, specificity 68%, area under the curve: 0.77). However, optimal cut-off values of 0.30 and 0.66 yielded a sensitivity and specificity of 100% and 96%, respectively. Kaplan-Meier analysis revealed a shorter median obliteration time for high-sphericity AVMs (> 0.41) compared with low-sphericity AVMs (45 vs. 60 months, P = 0.001). Among patient-related and morphological parameters, sphericity was associated with earlier AVM obliteration (hazard ratio: 36.29, 95% confidence interval: 2.89-454.37, P = 0.005), although it did not remain an independent predictor in multivariate analysis.

This preliminary study found that higher AVM nidus sphericity was associated with increased obliteration rates and shorter time to obliteration following GKRS. Although not an independent predictor, sphericity exhibited a more stable distribution than volume, suggesting its potential as a complementary 3D biomarker for predicting radiosurgical outcomes of AVMs.

AVM nidus sphericity may serve as a practical 3D geometric biomarker for predicting long-term outcomes following GKRS.