Topographic Classification of Middle Cerebral Artery M1 Segment Aneurysms: anatomical and microsurgical findings from a retrospective surgical series

Classificação Topográfica dos Aneurismas do Segmento M1 da Artéria Cerebral Média: achados anatômicos e microcirúrgicos de uma série cirúrgica retrospectiva

• Daniel Serfaty Fonseca    
• Hung Tzu Wen    
• Saul Almeida da Silva    
• Deisiane da Silva Mesquita Serfaty    
• Lucianna Serfaty de Holanda    
• Eberval Gadelha Figueiredo    

• https://doi.org/10.22290/jbnc.2026.14081140
• J Bras Neurocirur 37 (4):480-487, 2026

Resumo

Introdução: Os aneurismas do segmento M1 apresentam desafios microcirúrgicos relacionados à variabilidade anatômica, à proximidade dos ramos perfurantes e à escassez de descrições topográficas padronizadas. Objetivo: Descrever uma classificação em quatro quadrantes no plano posteroanterior (PA) para aneurismas de M1 e avaliar sua associação com projeção sagital, morfologia do M1 e ruptura intraoperatória (RIO). Métodos: Revisamos retrospectivamente 86 pacientes submetidos à clipagem microcirúrgica por um único cirurgião sênior entre 2006 e 2018. Os aneurismas foram classificados como superolaterais, inferolaterais, inferomediais ou superomediais em imagens PA. Projeção sagital e morfologia do M1 foram avaliadas independentemente. Resultados: O quadrante inferolateral foi o mais frequente (62,3%). A topografia PA associou-se à projeção sagital (p=0,034); aneurismas mediais foram predominantemente anteriores em comparação aos laterais (88,9% vs. 50,0%; p=0,035). A RIO ocorreu em 10,5% dos casos. A morfologia curva do M1 mostrou tendência não significativa de maior RIO (OR 3,18; p=0,075), enquanto a clipagem temporária associou-se significativamente à RIO (OR 6,80; p=0,020). Conclusão: A classificação PA oferece uma estrutura simples para descrição dos aneurismas de M1. O risco cirúrgico parece estar mais relacionado à morfologia do vaso parental e à complexidade intraoperatória do que à posição em quadrante isoladamente.

Palavras-chave

Aneurisma intracraniano; Artéria cerebral média; Microcirurgia; Procedimentos neurocirúrgicos; Complicações intraoperatórias; Anatomia

Abstract

Introduction: M1 segment aneurysms remain challenging because of anatomical variability, perforator proximity, and limited standardized topographic descriptions for operative planning. Objective: To describe a four-quadrant posteroanterior (PA) classification for M1 aneurysms and evaluate its association with sagittal projection, M1 morphology, and intraoperative rupture (IOR). Methods: We retrospectively reviewed 86 patients who underwent microsurgical clipping by a single senior surgeon between 2006 and 2018. Aneurysms were classified as superolateral, inferolateral, inferomedial, or superomedial on PA imaging. Sagittal projection and M1 morphology were independently assessed. Results: The inferolateral quadrant was the most frequent location (62.3%). PA topography was associated with sagittal projection (p=0.034); medial aneurysms were predominantly anterior compared with lateral lesions (88.9% vs. 50.0%; p=0.035). Overall IOR occurred in 10.5% of cases. Curved M1 morphology showed a non-significant trend toward higher IOR (15.4% vs. 6.4%; OR 3.18; p=0.075), whereas temporary clipping was significantly associated with IOR (33.3% vs. 6.8%; OR 6.80; p=0.020). Conclusion: This PA-based classification offers a simple descriptive framework for M1 aneurysms. Surgical risk appears more closely related to parent-vessel morphology and intraoperative technical complexity than to quadrant position alone.

Keywords

Intracranial aneurysm; Middle cerebral artery; Microsurgery; Neurosurgical procedures; Intraoperative complications; Anatomy

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1Division of Neurosurgery, Hospital das Clínicas, Faculdade de Medicina, Universidade de São Paulo – USP, São Paulo, SP, Brasil.

2Graduate Program in Neurology, Faculdade de Medicina, Universidade de São Paulo – USP, São Paulo, SP, Brasil.

3Graduate Program in Public Health and Environment – PPGSPMA, Oswaldo Cruz Foundation – FIOCRUZ, Rio de Janeiro, RJ, Brasil.

4Hospital das Clínicas Gaspar Vianna, Belém, PA, Brasil.

 

Received May 25, 2026 

Accepted May 30, 2026