Endoscopic Endonasal Transclival Approach Vs Dual Transorbital Port Technique for Clip Application to the Posterior Circulation: an Anatomic and Cadaveric Cerebral Perfusion Simulation Study

Background: Intracranial aneurysms of the posterior circulation are technically challenging to treat. Endoscopic endonasal approaches (EA) for treating posterior circulation aneurysms are a recent advancement in the field. Instrumentation must be manipulated in a confined compartment and angled for appropriate visualization. The technical expertise required to clip aneurysms via an endoscopic approach requires both a careful appreciation of vascular anatomy and adequate training. Simulation offers an excellent opportunity for neurosurgical and otolaryngology training regarding endoscopic techniques. 66% of residents participating in a recent simulation course agreed that simulation is a good complement to operative experience, and 33% strongly agreed. We show a feasible and replicable anatomic and simulation study that can be used to demonstrate EA transclival and transorbital portal approaches (TOPA) to the brainstem and posterior circulation.

Methods: Cadaveric specimens were all prepared at OHSU in accordance with the body donation program and VirtuOHSU laboratories. The cadavers were utilized to illustrate the anatomy of the posterior circulation were prepared with an embalming and microfil injection technique. Other cadavers were prepared fresh and preserved in formalin. Each cadaver was utilized innumerable times to demonstrate the reproducibility of this technique for simulation training and cost effectiveness. The EA transclival and TOPA were performed in each cadaver. The degrees of freedom, angles of visualization, ergonomics, multi-angled aneurysm clip and applier were evaluated.

Results: The EA transclival approach was successful in exposing the arteries of the posterior circulation, the 3rd cranial nerves, and ventral brainstem. Vascular control was best obtained via a bi-nostril technique. Adequate working space was obtained with this approach for placement of the endoscope as well as surgical instrumentation through the bilateral nasal passages. Enhanced degrees of visualization were obtained with the 0, 30, and 45 degree endoscopes. The multi-angled aneurysm clips on a single shaft applier were successfully positioned on the major arteries of the posterior circulation, which was appreciated by both pictures and video. This demonstrated both proximal vascular control and feasibility of aneurismal clipping. The purely EA transclival approach was superior to the EA transclival and TOPA due to better visualization of the posterior circulation above the level of AICA. The view of the posterior circulation via a zero degree endoscope via the TOPA alone was limited by the pituitary gland above the level of the AICA. However, it did improve the functional working area. The EA transclival alone provided better visualization of the basilar apex, PCA, and SCA’s bilaterally. Both approaches required superior or superolateral pituitary gland mobilization to provide excellent visualization and aneurysm clip application/removal.

Conclusions: In this EA transclival and transorbital anatomic and simulation study, we successfully demonstrate the technical considerations to optimize visualization, aneurysm clip application/removal and vascular control of the posterior circulation. With advances in technology and simulated cadaveric training, endoscopic endonasal approaches may become a safer and more widely utilized approach for aneurysm treatment. This model transcends aneurysm clipping specifically, in that it prepares learners as to the steps needed to the clivus as it pertains to tumor or neurovascular surgery.