Endoscopic Vascular Anatomy of the Retroclival Junction

Objectives: The purpose of this study is to examine the endoscopic vascular anatomy of the clival region (CR) in cadavers in order to determine the feasibility of vascular control during endoscopic endonasal approach to the retroclival area (RCA).

Methods: Modified endonasal endoscopic approaches were performed using rigid endoscopes (4 mm diameter, 18 cm length, 0° lenses) in five formalin-fixed cadaveric heads injected with colored silicone to study the RCA and adjacent structure. Retroclival regions were divided in three segments—upper, middle and lower. We studied the length of posterior vascular exposure of each segment and the adjacent anatomy. Vascular exposure was marked with hemoclips, and segments between clips were measured in situ and in radiographs.

Results: The upper segment, bounded posteriorly by the dorsum sellae in the midline and the posterior clinoids in the paramedian region, was exposed after pituitary transposition. Average width was 10.8 mm (range, 10–12 mm). Basilar artery length averaged 7.4 mm (range, 6–8 mm). Endoscopic control of P1 and proximal superior cerebellar artery (SCA) was obtained.

The middle segment, extending from the sellar floor superiorly and a projected line between both paraclival carotids at the vidian intersection inferiorly, had an average length of 15 mm (range, 15–16 mm) and a trapezoidal shape. Upper width averaged 14.6 mm (range, 12–20 mm); lower width averaged 12.2 mm (range, 10–14 mm). The anterior inferior cerebellar arteries (AICAs) were followed laterally to expose an average of 4.6 mm (range, 3–7 mm) on the right and 3.2 mm (range, 1–5 mm) on the left.

The lower segment was exposed by removing the lower third of the clivus, extending from cranial nerve VI at the pontomedullary sulcus to the inferior border of the basiocciput. The vertebrobasilar junction was exposed, and the anterior spinal artery was visualized in 60% of specimens. Upper width of this segment averaged 12.2 mm (range, 10–14 mm), and the lower width averaged 9.4 mm (range, 11–8). Length of exposure of the right vertebral artery (VA) was 8.2 mm (range, 4–13 mm); the left VA was 7.2 mm (range, 2–13 mm).

Conclusion: Exposure of the RCA using the modified endoscopic endonasal approach allowed for exposure of the vertebrobasilar complex vessels, and the proximal branches are also feasible, potentially affording vascular control. Further anatomic studies are required to establish the potential clinical applications of these results.