M1 segment morphology and temporary clipping during middle cerebral artery aneurysm surgery: a single-center surgical cohort

Background Microsurgical planning for middle cerebral artery (MCA) aneurysms usually emphasizes aneurysm size, rupture status, dome projection, neck configuration, and branch incorporation. The preoperative course of the parent M1 segment may also influence exposure and proximal control. This single-center surgical cohort evaluated whether M1 morphology is associated with temporary clipping during MCA aneurysm surgery. Methods Adult patients who underwent microsurgical clipping of MCA aneurysms involving the M1-bifurcation complex between 2006 and 2018 were retrospectively analyzed. M1 morphology was independently classified on preoperative vascular imaging as straight, upward-curved, or downward-curved by two senior cerebrovascular neurosurgeons. Temporary clipping was the primary outcome. Analyses were descriptive and unadjusted because of limited event counts. Results Eighty-six patients were included. Interobserver agreement for M1 classification was 95.3% (Cohen’s kappa = 0.92). M1 morphology was straight in 47 patients (54.7%), upward-curved in 27 (31.4%), and downward-curved in 12 (14.0%). Temporary clipping was used in 3 of 47 straight M1 cases (6.4%), 6 of 27 upward-curved cases (22.2%), and 4 of 12 downward-curved cases (33.3%; p = 0.041). In the straight-versus-curved analysis, temporary clipping was used in 3 of 47 straight cases (6.4%) and 10 of 39 curved cases (25.6%). Curved M1 morphology was associated with higher unadjusted odds of temporary clipping (odds ratio 5.06, 95% confidence interval 1.28–19.96; p = 0.017). Intraoperative rupture was numerically more frequent in curved anatomy, whereas multiple-clip use was similar. Conclusions Curved M1 morphology was associated with greater temporary clipping use during MCA aneurysm clipping. Temporary clipping was interpreted as a technical marker of proximal control demand rather than as a complication. These single-center, unadjusted findings are hypothesis-generating, do not establish causality, and require external validation. The study was not designed to assess postoperative clinical or angiographic outcomes.