Stent-Assisted Coil Embolization of MCA Bifurcation Aneurysms at a Hypoplastic M1 Branch by Use of Hook Technique

Background: We describe the Hook technique enabling coil embolization in unfavorable M1 bifurcation aneurysms and analyze the morphologic variations in M1 bifurcation to evaluate how often such aneurysms can be seen. Methods: Among 42 MCA aneurysms treated by stent-assisted coil embolization, aneurysms arising at the acute-angled hypoplastic M1 branch (n = 14) were treated by the Hook technique, in which a short stent was deployed only to protect the aneurysm neck after microcatheter selection of the hypoplastic M2, followed by subsequent coiling of the aneurysm. Outcome was evaluated, including Raymond classification, coil packing density, final modified Rankin Scale (mRS), and recurrence. Separately, 100 middle cerebral artery (MCA) bifurcation aneurysms were analyzed to assess the proportion of such unfavorable aneurysms. Results: Procedural success of the Hook technique was obtained in 13 of 14 patients (93%). A mean packing density of 30% was achieved. Magnetic resonance angiographic follow-up at a median 4 months (range, 1–26 months) showed complete occlusion in 11 patients and residual neck filling in 3 patients. There was no clinical event (mRS = 0) over a median 17 months (range, 2–26 months) of clinical follow-up. One patient had a thrombotic occlusion during the procedure, which was resolved after tirofiban infusion, without evidence of an infarct or deficit. Of the 100 MCA bifurcation aneurysms, aneurysm arising in asymmetric hypoplastic M2 division was the most common type (48%). Conclusions: The Hook technique enabled stent-assisted coiling of M1 bifurcation aneurysm with extension along the asymmetric hypoplastic M2 division and also securing the M2 branch.