Endonasal and transoral approaches to the craniovertebral junction: A quantitative anatomical study

Background: The endoscopic endonasal approach has recently been added to the surgical armamentarium to access the anterior craniovertebral junction (CVJ). Comparative analyses with the transoral approach are scarce. The aim of this study was to provide a quantitative anatomical analysis of both approaches. Methods: In four specimens the endoscopic endonasal approach (before and after sphenoidectomy) and the transoral approach (without and with a soft palate split) were performed. ApproachViewer—part of GTx-UHN (Guided Therapeutics software, developed at University Health Network, Toronto, ON, Canada)—was used to quantify and visualize the working volume, as well as the exposed area, of each surgical approach. Different modalities (crossing and non-crossing) were used to quantify the exposure of the deep surface, providing an indirect quantitative value of the ‘surgical freedom’. The lowest point exposed by the endonasal approaches was compared with that predicted by preoperative radiological lines. Non-parametric Welch analysis of variance (ANOVA) was used for statistical analyses. Results: The working volume was significantly larger and the distance to the target was shorter with the transoral approaches than with the endonasal approaches. Clival exposure was better with the endonasal approaches than with the non-crossing transoral approach without a soft palate split; areas below C1 were better exposed with the transoral routes. The nasoaxial line best predicted surgical exposure with the endonasal approaches. Conclusion: Endoscopic endonasal and transoral approaches to the anterior CVJ provide optimal exposure of different areas that overlap at the level of C1 when no anatomical anomalies are present. A split of the soft palate is not necessary during the transoral approach if it is combined with an endoscopic endonasal approach.