• Xinmin Ding, Peyton L Nisson, Whitney S James, Michael T Lawton, Shaohua Ren, Lu Jia, and Honging Ji.
• ShanXi Province People's Hospital, Yinze District, Taiyuan, China; Department of Neurosurgery, University of California, San Francisco, San Francisco, California, USA. Electronic address: ddrankey@163.com.
• World Neurosurg. 2017 Aug 1; 104: 291-302.

ObjectiveThis study aims to establish a new classification system for proximal anterior cerebral artery (A1) aneurysms and to offer treatment strategies, based on the lessons learned by studying the case reports of 41 patients with A1 aneurysms.MethodsA total of 2332 consecutive patients with intracranial aneurysms were treated at a single medical center between June 2005 and May 2015. Forty-one patients with 42 A1 aneurysms were treated by surgical clipping or endovascular coiling. Clinical data, radiographic results, treatments, and patient outcomes were later collected and analyzed.ResultsOf 2332 intracranial aneurysm patients, 1.76% (n = 41) had a total of 42 A1 aneurysms. Twenty-six of these (62%) were proximal A1 segment aneurysms, 9 (21%) were distal A1 segment aneurysms, and 7 (17%) were fusiform A1 aneurysms. A1 aneurysms can be classified into 3 main types. Types IA and IB originate from the posterior wall of the proximal A1 segment. Type IA projects posterior-inferiorly, whereas type IB projects posterior-superiorly. Type IIA originates from the distal trunk of the A1 artery. Type IIB originates from an angle of an abnormal cortical branch or a ring of an A1 arterial fenestration. Type III consists of fusiform or dissecting aneurysms located anywhere along the A1 segment. After studying the range of treatments and outcomes, when treating these complex morphologies, we recommend clipping type I and II A1 aneurysms and embolizing type III A1 aneurysms.ConclusionsA1 artery aneurysms are a rare type of aneurysm with unique characteristics. The classification system proposed here accurately summarizes these characteristics to better guide treatment strategies.Copyright © 2017 Elsevier Inc. All rights reserved.

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