Anterior Cerebral Artery: ACA trifurcation - Ep.1/2

Endovascular Treatments for Complex Bifurcated Cerebral Aneurysms 

Wide-neck aneurysms are more likely to arise from bifurcated or trifurcated locations including the middle cerebral artery, anterior communicating artery complex, basilar tip, or internal carotid artery terminal other than the junction with the posterior communicating artery in ruptured cases. Wide-neck bifurcation aneurysms (WNBAs) often require advanced endovascular techniques beyond primary coiling to achieve adequate aneurysm occlusion. Occasionally, more complex cases even require parent artery occlusion with high-flow bypass. 

Primary Treatment Strategies

Double stent assisted coiling

Stent-assisted coiling with double stents has been widely used for the treatment of complex and wide-neck bifurcation aneurysms before the era of intrasaccular devices. The geometry of double stent configurations varies with “Y”, “T”, “half-T” for bifurcation and “X”, “H” for trifurcation, according to configurations of parent arteries and branches needed to be protected. Double stent configurations carry technical complexity to achieve, and would establish a new hemodynamic status and set obstacles for possible retreatment. Take Acom aneurysm as an example, the balanced bilateral A1 and A2 configuration treated with H stent might establish the most preferrable hemodynamic status to restrict flow into the aneurysm; while unbalanced geometries with hypoplastic or atretic A1 would be expected to associate with higher thromboembolic and regrowth risks treated with Y-stent assisted coiling.

Combined remodeling technique

Complex wide-necked bifurcated aneurysms could also be treated with stent plus balloon-assisted coiling with low-profile braided stents delivered through dual-lumen balloon. This combined aneurysm neck remodeling technique enables adequate aneurysm occlusion without double stent implantation and spare more space for future treatment. Although overall complication risks increase, safety and efficacy for MCA bifurcation aneurysms are acceptable.

Flow diversion

New low-profile flow diverters delivered through 0.017-inch microcatheter have expanded their application to distal fusiform aneurysms or branches of bifurcated aneurysms, such as M2, A2, etc. Beyond primary flow diversion effect, flow diverter implantation might also change configurations and hemodynamics of parent artery related to development and growth of aneurysms to further reduce recurrence risks.  

Intrasaccular flow diversion and intrasaccular neck bridging

Intrasaccular devices primarily designed for WNBAs can be particularly useful for complex aneurysms with unfavorable anatomy, such as fusiform aneurysms. The delivery systems for these devices are more favorable to apex aneurysms compared to side-wall aneurysms. However, current available intrasaccular devices could be applied to up to approximately 10mm aneurysms.

Another strategy to reduce thrombogenicity while remodeling aneurysm neck is intrasaccular or extrasaccular neck bridging with devices like Nautilus and eCLIPs. The non-tubular eCLIPs acts like Y stenting without coverage of branches to reduce thromboembolic complications, and are suitable for aneurysm neck width up to 12mm. The device delivery process is similar to swinging-tail technique in stent assisted coiling.

Combined abovementioned strategies and hybrid procedures have been reported for complex cases. However, it’s always safer to keep procedures as simple as possible when technically feasible. 

Retreatment Strategies

Wide neck aneurysm obliteration rate is relatively low and the recurrence and retreatment rate is high treated with primary coiling, especially for giant or fusiform aneurysms. Recurrent aneurysms after stent-assisted coiling could be effectively and safely retreated with flow diversion, the primary stents were mainly close-cell or braided stents. Both proximal and distal ends of the flow diverter should contact the normal parent artery to span the entire length of the previous stent. However, a previous stent endoleak may reduce flow diversion efficacy contraindicated for this strategy. In case of intrasaccular flow diverter, roughly 10% of WNBAs initially treated with the WEB device will undergo retreatment, among them Acom aneurysms were most common. Reported strategies include stent-assisted coiling, flow diverters, another intrasaccular devices, or even open surgery. But complication risks are relatively high compared with primary treatment. 

References

1.         Hagen F, Maurer CJ, Berlis A. Endovascular Treatment of Unruptured MCA Bifurcation Aneurysms Regardless of Aneurysm Morphology: Short- and Long-Term Follow-Up. AJNR Am J Neuroradiol. 2019 Mar;40(3):503-509. doi: 10.3174/ajnr.A5977.

2.         Park KY, Yeon JY, Kim BM, Jeon P, Kim JH, Jang CK, Kim DJ, Lee JW, Kim YB, Chung J, Song DH, Park HG, Park JS. Efficacy and Safety of Flow-Diverter Therapy for Recurrent Aneurysms after Stent-Assisted Coiling. AJNR Am J Neuroradiol. 2020 Apr;41(4):663-668. doi: 10.3174/ajnr.A6476. 

3.         Cimflova P, et al. Long-term safety and efficacy of distal aneurysm treatment with flow diversion in the M2 segment of the middle cerebral artery and beyond. J Neurointerv Surg. 2021 Jul;13(7):631-636. doi: 10.1136/neurintsurg-2020-016790. 

4.         Schüngel MS, et al. Endovascular Treatment of Intracranial Aneurysms in Small Peripheral Vessel Segments-Efficacy and Intermediate Follow-Up Results of Flow Diversion With the Silk Vista Baby Low-Profile Flow Diverter. Front Neurol. 2021 May 28;12:671915. doi: 10.3389/fneur.2021.671915. 

5.         Kan P, Sweid A, Srivatsan A, Jabbour P. Expanding Indications for Flow Diverters: Ruptured Aneurysms, Blister Aneurysms, and Dissecting Aneurysms. Neurosurgery. 2020 Jan 1;86(Suppl 1):S96-S103. doi: 10.1093/neuros/nyz304.

6.         Srinivasan VM, et al. Retreatment of Residual and Recurrent Aneurysms After Embolization With the Woven EndoBridge Device: Multicenter Case Series. Neurosurgery. 2022 May 1;90(5):569-580. doi: 10.1227/neu.0000000000001883.

7. Sahnoun M, Soize S, Manceau PF, Gelmini C, Pierot L. Intracranial aneurysm treatment with WEB and adjunctive stent: preliminary evaluation in a single-center series. J Neurointerv Surg. 2022 Feb;14(2):164-168. doi: 10.1136/neurintsurg-2021-017379.