Aneurysm location alone fails to predict need for multiple clips in MCA surgery

Neurosurgeons planning to clip an aneurysm of the middle cerebral artery have long used the lesion’s position along the vessel as an early clue to how difficult the operation might be. A new retrospective cohort study now offers a quantitative caution against relying on that clue alone. In a single-center series of 86 microsurgical clipping operations, aneurysms involving the artery’s bifurcation were not more likely to require multiple permanent clips than aneurysms arising on the M1 trunk segment. What did matter, after statistical adjustment, was aneurysm size: non-small lesions carried roughly sixfold higher adjusted odds of a multiple-clip construct.

The study, published in the Egyptian Journal of Neurosurgery, set out to test a specific hypothesis. Segmental location changes the arterial and branch relationships a surgeon encounters during middle cerebral artery aneurysm clipping, but its ability to anticipate a multiple-clip reconstruction had remained uncertain. The researchers, led by a senior cerebrovascular neurosurgeon at a tertiary academic center, asked whether bifurcation involvement, which is knowable before surgery and easy to communicate, could identify operations in which a single clip would not suffice to reconstruct the vessel’s closure line.

The methods were deliberately straightforward. The source database contained 107 adults who underwent transcranial microsurgical clipping of a saccular middle cerebral artery aneurysm between 2006 and 2018, all under the supervision of the same senior surgeon using a pterional approach. Twenty-one records were excluded because the segmental aneurysm location had not been documented with sufficient specificity, leaving 86 operations for the location analysis. Fusiform, traumatic, and mycotic lesions, along with primary endovascular treatments, were not eligible for the source surgical cohort. The unit of analysis was the index aneurysm operation itself.

The exposure of interest was grouped into two primary categories. Bifurcation-involving lesions, meaning aneurysms recorded as bifurcation or as combined bifurcation and proximal M1, totaled 62 operations. M1-segment lesions, recorded as proximal or distal M1, totaled 24. The four individual categories were also retained for descriptive and exact sensitivity analysis: 60 pure bifurcation cases, 2 combined bifurcation-proximal cases, 14 proximal M1 cases, and 10 distal M1 cases. The outcome was operationally defined as the use of at least two documented permanent clips, a threshold drawn from a numerical clip-count field rather than a subjective judgment of complexity.

The headline result was a statistical null. Multiple-clip reconstruction occurred in 31 of the 86 operations, or 36.0 percent. It was used in 21 of 62 bifurcation-involving operations, 33.9 percent, and in 10 of 24 M1-segment operations, 41.7 percent. The unadjusted exact odds ratio for bifurcation-involving versus M1-segment location was 0.72, with a 95 percent confidence interval of 0.25 to 2.14 and a p value of 0.618. Across all four recorded location categories, multiple-clip use ranged only from 33.3 percent in pure bifurcation cases to 50.0 percent in the two combined bifurcation-proximal cases, with 42.9 percent for proximal M1 and 40.0 percent for distal M1, and the Fisher-Freeman-Halton exact test returned a p value of 0.817.

Adjustment did not rescue the location hypothesis. In a parsimonious logistic regression model that included the location contrast, aneurysm size category, and the presence of multiple aneurysms, bifurcation involvement remained unassociated with the outcome, with an adjusted odds ratio of 0.61 and a 95 percent confidence interval of 0.22 to 1.73. The presence of multiple aneurysms was likewise not independently associated, at an adjusted odds ratio of 0.60. Non-small aneurysm category, however, was independently associated with multiple-clip reconstruction, with an adjusted odds ratio of 5.99, a 95 percent confidence interval of 1.93 to 18.56, and a p value of 0.002. Descriptively, multiple clips were used in 18 of 67 small-category operations, 26.9 percent, compared with 13 of 19 non-small operations, 68.4 percent.

Sensitivity analyses reinforced these patterns. Excluding the two combined bifurcation-proximal records left the location estimate essentially unchanged, at an adjusted odds ratio of 0.58. Adding ruptured presentation to the adjusted model produced a similar estimate of 0.60. When the outcome threshold was made stricter, requiring at least three permanent clips, 8 of 62 bifurcation-involving and 4 of 24 M1-segment operations met the criterion, yielding a conditional odds ratio of 0.74 with a p value of 0.731. Overall, one permanent clip was documented in 55 operations, two clips in 19, and at least three clips in 12.

The authors are careful about what these numbers do and do not mean. The clinically relevant message, they write, is not that segmental location is unimportant. Location determines which arterial structures are exposed and which branches must be preserved, and proximal M1 aneurysms can arise near early cortical branches and lenticulostriate perforators while bifurcation aneurysms may incorporate or splay the M2 trunks. Rather, the findings indicate that location is not a sufficient proxy for the morphology that determines whether a single clip can reproduce the desired closure line. Multiple-clip strategies appeared in every recorded segmental category, and the confidence intervals around the two primary group proportions overlapped substantially.

The association with size is technically plausible, the authors argue. Increasing lesion size can lengthen the closure line, broaden the neck, and amplify curvature, raising the probability that a single clip blade pair will not close the lesion while preserving adjacent vessels. Size is not the only relevant feature, however: lobulation, neck width, calcification, thrombus, branch incorporation, and perforator relationships can all shape the final construct. The database did not measure these features consistently, so the size estimate should be read as a marker of morphology rather than a complete predictive model. The study also carries the limitations of its retrospective, single-center design, the exclusion of 21 records without specific location documentation, and coarse size categories, and clip count was a purely technical endpoint that says nothing about occlusion quality, vessel patency, or neurological outcome.

For surgical planning, the practical implication is to avoid a deterministic assumption that bifurcation aneurysms will demand multiple clips while M1 aneurysms will not. The operative team should keep an appropriate range of clip lengths, curvatures, fenestrations, and applicator angles available across all middle cerebral artery locations, and a non-small lesion should heighten readiness for a reconstructive sequence. When multiple clips are used, direct inspection and available intraoperative flow assessment remain important, because cumulative clip geometry can distort or compromise adjacent vessels. The study was approved by the Research Ethics Committee of Hospital das Clinicas da Faculdade de Medicina da Universidade de Sao Paulo, with the requirement for informed consent waived because it used retrospective secondary clinical and imaging data.

Subject of Research: The association between middle cerebral artery aneurysm segmental location and the use of multiple-clip reconstruction in microsurgical clipping

Article Title: Segmental location and multiple-clip reconstruction in middle cerebral artery aneurysm surgery: a retrospective cohort

Article References: Serfaty-Fonseca, D., Hung Tzu, W., Almeida da Silva, S., Serfaty, D. D. S. M., Serfaty-de-Holanda, L., & Figueiredo, E. G. (2026). Segmental location and multiple-clip reconstruction in middle cerebral artery aneurysm surgery: a retrospective cohort. Egyptian Journal of Neurosurgery, 41(1), Article 181. https://doi.org/10.1186/s41984-026-00689-6

Image Credits: AI Generated

DOI: 10.1186/s41984-026-00689-6

Keywords: middle cerebral artery, aneurysm clipping, multiple-clip reconstruction, segmental location, retrospective cohort, bifurcation aneurysm, M1 segment, aneurysm size, surgical planning, cerebrovascular surgery, odds ratio, microsurgery