• Hirotaka Hasegawa, Shunya Hanakita, Masahiro Shin, Takehiro Sugiyama, Mariko Kawashima, Wataru Takahashi, Masaaki Shojima, Osamu Ishikawa, Hirofumi Nakatomi, and Nobuhito Saito.
• Department of Neurosurgery, University of Tokyo Hospital, Tokyo, Japan. Electronic address: hirohasegawa-tky@umin.ac.jp.
• World Neurosurg. 2018 Aug 1; 116: e556-e565.

ObjectiveStereotactic radiosurgery is widely used to treat brain arteriovenous malformation; however, detailed information on late radiation-induced complications (LRICs) is scarce. The goal of the present study was to characterize the incidence, risk factors, and clinical outcomes of LRICs based on our long-term follow-up data.MethodsThe outcomes of consecutive patients who underwent stereotactic radiosurgery for arteriovenous malformations at our institution in 1990-2010 were analyzed. Cyst formation/encapsulated hematoma (CF/EH) and radiation-induced tumor were defined as LRICs. Cumulative incidence rates were calculated using the Kaplan-Meier method. Risk factors for CF/EH were analyzed using a Cox proportional hazard model.ResultsA total of 581 patients with mean and median follow-up periods of 11.8 and 10.1 years, respectively (range, 2.0-26.7 years), were analyzed. CF/EH was observed in 30 patients (5.2%). The median time to progression was 11.8 years (range, 1.9-23.9 years). Cumulative incidence rates were 0.8%, 2.8%, 7.6%, and 9.7% at 5, 10, 15, and 20 years, respectively. A multivariate analysis showed that lobar location and maximal diameter ≥22 mm were significant risk factors for CF/EH. Overall, the functional outcomes were mild, moderate, and severe/fatal in 26 (87%), 1 (3%), and 3 (10%) patients, respectively. Radiation-induced tumor was confirmed in only 1 patient (0.17%).ConclusionsAn increased nidus size and lobar location are risk factors for CF/EH. Although the CF/EH incidence is low, some LRICs develop after long periods. Extended follow-up is warranted, particularly of patients with risk factors.Copyright © 2018 Elsevier Inc. All rights reserved.

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