Microsurgical resection of brain arteriovenous malformations with or without preoperative embolization: a 10 year observational cohort study.

[OBJECTIVES] The role of preoperative embolization as an adjunct to microsurgical resection of brain arteriovenous malformations (AVMs) remains uncertain. We evaluated clinical and angiographic outcomes of microsurgical resection performed with or without preoperative embolization and examined factors associated with selection for embolization.

[METHODS] We conducted a retrospective observational cohort study of consecutive patients undergoing microsurgical resection of AVMs at a tertiary centre between July 2015 and June 2025. Patients treated with microsurgery alone or with preoperative embolization were included. Baseline differences were addressed using propensity score methods, including 1:3 matching and inverse probability of treatment weighting. The primary outcome was treatment related morbidity at 90 days, defined as an increase of at least 1 point on the modified Rankin Scale (mRS). Secondary outcomes included functional dependence (mRS greater than 2), postoperative haemorrhage, parenchymal infarction, angiographic obliteration, operative duration and composite outcome of mRS deterioration of at least 2 points or death at 90 days. Factors associated with embolization use were evaluated with Firth penalized logistic regression, and discriminative performance of AVM size was assessed using receiver operating characteristic analysis.

[RESULTS] Among 104 patients, 91 (87.5%) underwent microsurgical resection alone and 13 (12.5%) underwent preoperative embolization followed by microsurgery. Embolized AVMs were larger (mean 3.8 vs 2.5 cm), more frequently demonstrated deep perforator supply, and were of higher Spetzler-Martin grade. After propensity score adjustment, no clear differences were observed in treatment related morbidity at 90 days (risk difference + 23.1%, 95% CI - 3.3 to 51.9), functional dependence (risk difference + 20.5%, 95% CI - 8.5 to 49.7), the composite outcome of mRS deterioration of at least 2 points or death, or mortality. AVM size was independently associated with embolization use (odds ratio 1.77 per cm increase), with moderate discriminative performance (AUC 0.76). A 3 cm threshold demonstrated the strongest association with embolization selection.

[CONCLUSION] In this single centre observational cohort, microsurgical resection with or without preoperative embolization was associated with similar short term functional and angiographic outcomes after adjustment for baseline differences, although estimates were imprecise. AVM size was the primary factor associated with selection for embolization, but this did not correspond to a demonstrable outcome advantage. These findings reflect contemporary practice patterns and underscore the need for prospective multicentre studies to clarify whether embolization confers incremental benefit in selected patients.

[ABBREVIATIONS] AVM, arteriovenous malformation; mRS, modified Rankin Scale; CI, confidence interval; AUC, area under the curve; mFI-5, modified 5-item frailty index; SM, Spetzler-Martin; Supp-SM, Supplemented Spetzler-Martin.