The Anterior Incisural Width as a Preoperative Indicator for Intradural Space Evaluation: An Anatomical Investigation

Objective: The opticocarotid triangle (OCT) and the caroticooculomotor triangle (COT) are two anatomical triangles used in accessing the basilar region. We conducted a morphometric study to evaluate the anterior incisural width (AIW) as an indicator to predict the intraoperative exposure via both triangles.

Methods: Twenty sides of ten cadaveric heads were dissected and analyzed. The heads were divided into groups: group A, narrow anterior incisura and group B, wide anterior incisura, using 26.6 mm as a cut-off distance of the AIW. The area of the COT and the OCT in the transsylvian approach was measured. The maximum widths via the two trajectories in a modified superior transcavernous approach were measured. The areas and the widths of the triangles were compared between the narrow and wide groups.

Results: The COT in the wide group was shown to have a significantly larger area compared with the COT in the narrow group (38.4 ± 12.64 vs. 58.3 ± 15.72 mm, p < 0.01). No difference between the two groups was reported in terms of the area of the OCT (50.9 ± 19.22 mm vs. 63.5 ± 15.53 mm, p = 0.20), the maximum width of the OCT (6.6 ± 1.89 vs. 6.5 ± 1.38 mm, p = 1.00), or the maximum width of the COT (11.7 ± 2.06 vs. 12.2 ± 2.32 mm, p = 0.50).

Conclusion: An AIW less than 26.6 mm is an unfavorable factor related with a limited COT area in a transsylvian approach for pathologies at the interpeduncular fossa such as basilar apex aneurysms at the level of the posterior clinoid process. Preoperative identification and measurement of a narrow AIW can suggest the need to add a transcavernous approach. The approach selection should be individualized based on multiple related factors comprehensively.

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