Totally Intracranial High-Flow Bypass: Morphometric Study with Dynamic Validation in a Fresh Cadaver Training Model Using a Continuous Extracorporeal Circulation System

Introduction: The introduction of endovascular techniques for the treatment of cerebrovascular disease has not only improved the outlook, but has also expanded the horizons in treatment for patients’ complex cerebrovascular disease. However, many conditions remain where endovascular methods have no proven efficacy, leaving surgical revascularization as the only alternative. Realistic training models for surgical cerebral revascularization are lacking; this underscores their need to achieve proficiency on bypass procedures. We describe a technique for high-flow bypass in a fresh cadaveric model with the incorporation of an extracorporeal circulating blood system that resembles clinical conditions, adding technologies used in the clinical setting for assessment of the anastomosis efficacy. The anatomical basis for the proposed high-flow bypass technique using an interposition radial artery graft from the petrous carotid as a donor exploring the supraclinoid internal carotid and the middle cerebral artery as putative recipients is discussed using a detailed morphometric analysis.

Methods: Ten cadaveric heads were used for this study. On seven embalmed heads, we performed a morphometric analysis of the subtemporal approach for exposure of the petrous (C2 segment) internal carotid artery (ICA) as a donor vessel for an interposition radial artery graft for bypass and a comparative analysis of two putative ipsilateral recipients for bypass, the supraclinoid ICA, and the M2 segment of the middle cerebral artery (MCA), using in situ measurements and neuronavigation. Subsequently, a dynamic intracranial bypass model was developed in three fresh heads using a continuous circulation system using pig blood, complemented by an objective, consistent and reliable method for assessment of the bypass technique using transcranial Doppler, intraarterial flow measurement, and indocyanine green (ICG) angiography.

Results: After using all available surgical maneuvers for maximum exposure, the horizontal segment of C2 averaged 18.9 mm (range: 14.7–22.7 mm), highlighting high variability among specimens. Comparative analysis of supraclinoid ICA and M2 as potential graft recipients favored the latter, which presented less technical complexity for exposure and graft suturing, wider surgical window and operative space volume. Successful C2 ICA to M2 was completed in all 3 fresh head. Patency was confirmed with qualitative Doppler, quantitative Doppler (MCA velocities average: 55 cm/second), and ICG angiography. Postoperative CT scan with radiopaque colored silicone injected through the ipsilateral carotid showed antegrade distribution through the graft and revascularized MCA territory.

Conclusion: This morphometric study validated by a fresh cadaver perfusion model confirmed the feasibility of a totally intracranial, short segment interposition graft high-flow bypass, delivering hemodynamic features in line with those of normal flow of the MCA in the clinical setting. Whereas this technique and model have been developed as a training model for continuous monitoring and improvement of the technique of high-flow bypass, the possibility of its application in the clinical setting arises in select cases.