Impact of Microcatheter Position on Mechanical Stress in Intracranial Aneurysms

Background Endovascular coiling for intracranial aneurysms may lead to intraoperative rupture, a potentially devastating complication, with approximately 70% of events occurring during coil insertion. However, the factors responsible for generating mechanical stress are still not well defined. We aimed to identify how catheter positioning and the stage of coil delivery affect aneurysm wall stress using an in vitro model. Methods An anterior communicating artery aneurysm model was employed under physiologic temperature and flow to measure insertion force as coils were advanced at a constant rate of 2 mm/sec. Experiments tested two intermediate catheter (IMC) positions (distal A1 and proximal cavernous) combined with two microcatheter tip locations: close to the aneurysm wall (apex) or distant from the wall (neck). Four commercially available coil types were evaluated with 10 repeated trials. Analyses applied two‐way repeated‐measures ANOVA (factors: distance and microcatheter position) separately for each IMC position; force is reported as percent change from the −12 to −9 mm bin (set to 100%). Results As the coil advanced toward detachment, insertion force increased under all conditions, with a rise when the microcatheter tip was close to the apex compared with when it was positioned neck, regardless of IMC position. In the pooled four‐coil dataset, both main effects (coil insertion stage and microcatheter position) and their interaction were significant for distal (A1) and for proximal (cavernous) support (all p < 0.0001), indicating that the pre‐detachment slope is consistently greater when the tip is at the aneurysm wall. After passing the detachment point, force climbed further and reached a distinctly higher final level with the tip at the apex. Mean change at +0 to +3 mm was +50.2% for A1‐apex and +49.6% for cavernous‐apex, versus +11.9% (A1‐neck) and +5.6% (cavernous‐neck), corresponding to final levels ofabout 150% at the apex and about 110% at the neck. Subgroup analyses confirmed robustness across designs: every coil‐specific two‐way RM ANOVA showed a significant coil insertion stage × microcatheter tip location. Conclusions With the microcatheter tip close to the wall, force rises more steeply as detachment approaches and, beyond detachment, even slight over‐advancement produces a larger jump and higher final force—independent of distal or proximal IMC support. Physicians should gently push coils as detachment point nears and avoid post‐detachment point over‐push to reduce mechanical stress and potential rupture risk, particularly when the microcatheter is placed close to the wall.