Transnasal Endoscopic and Lateral Approaches to the Clivus: A Quantitative Anatomic Study

Highlights

• Endoscopic endonasal approaches to the clivus have been recently described, and their benefits compared with transcranial approaches are a matter of debate.

• A novel quantitative research method has been systematically applied to evaluate endonasal endoscopic and lateral approaches to the clivus in the anatomy laboratory.

• We quantify the significant anatomic differences in working volume and exposure among the most frequently used approaches to the clivus, documenting the generally more significant values obtained by endonasal endoscopic approaches compared with lateral approaches.

Background

Transnasal endoscopic approaches to the clivus have been established recently. Comparative analyses with classic lateral approaches are limited. In this study, we compared transnasal endoscopic and lateral approaches to the clivus, quantifying the exposure and working volume of each approach in the anatomy laboratory.

Methods

High-resolution computed tomography scans were performed on 5 injected specimens (10 sides). In each specimen, transnasal endoscopic approaches (i.e., paraseptal, transrostral, extended transrostral, transethmoidal, and extended transclival without and with intradural hypophysiopexy) and lateral approaches (i.e., retrosigmoid, far-lateral, presigmoid retrolabyrinthine and translabyrinthine) to the clivus were performed. An optic neuronavigation system and dedicated software (ApproachViewer; Guided Therapeutics Program, University Health Network, Toronto, Ontario, Canada) were used to quantify the working volume and exposed clival area of each approach. Statistical evaluation was performed with the Kruskal–Wallis test and Steel–Dwass–Critchlow–Fligner post hoc test.

Results

Endoscopic transnasal transclival approaches showed higher working volume and larger clival exposure compared with lateral approaches. Incremental volumetric values were evident for transnasal approaches; presigmoid approaches provided less working volume than retrosigmoid approaches. A transnasal transclival approach with hypophysiopexy provided significant exposure of the upper clivus (84.4%). The transrostral approach was the first transnasal approach providing satisfactory access to the midclivus (66%); retrosigmoid and far-lateral approaches provided exposure of approximately one half of the midclivus. The lower clivus was optimally exposed with endoscopic transclival approaches (83%), whereas access to this region was limited with lateral approaches.

Conclusions

This quantitative anatomic study shows that endoscopic transnasal approaches to the clivus provide a larger working volume and wider exposure of the clivus compared with lateral approaches.

Introduction

In the past 2 decades, transnasal endoscopic surgery has become a cornerstone in the treatment of lesions of the skull base and adjacent areas.1, 2, 3, 4 However, the optimal surgical approach for lesions in challenging sites, such as the clival area, remains a matter of debate.5, 6, 7, 8, 9, 10, 11

Endoscopic transnasal transclival approaches (ETCAs) provide a median corridor to the clivus by exploiting the nasal cavities to create a working space that is free of major nerves and vessels. ETCAs can be subdivided in upper, middle, and lower routes, which can be combined according to the need for exposure and surgical maneuverability.¹² The lateral boundaries of the corridor can be expanded up to the cavernous sinus,13, 14 inferior petrosal sinus, and hypoglossal nerve.¹⁵

ETCAs have gained wide favor in recent years, replacing most median approaches to the clivus. They were first used for extradural disease involving the clivus and petroclival junction and have been progressively adopted to resect lesions with transdural and intradural extensions (e.g., chordomas,¹⁶ chondrosarcomas,⁹ meningiomas,¹⁷ aneurysms of the posterior fossa¹⁸). Their major drawback is the need for skull base reconstruction, which can be challenging due to the geometry, dimension, and site of the defect. In cases of intradural pathology, ETCAs are still associated with a relatively high postoperative cerebrospinal fluid (CSF) leak rate.6, 7, 17, 18, 19

Surgical options to expose the clivus include lateral transcranial corridors, with retrosigmoid⁷ and far-lateral¹⁹ approaches being the most widely used, together with retrolabyrinthine and translabyrinthine approaches. These approaches provide exposure of the clivus with a diagonal trajectory and involve crossing a number of neurovascular structures.

In this preclinical anatomic study, the most commonly used transnasal and lateral approaches to the clivus were compared using a novel research tool based on an optic neuronavigation system and dedicated software that quantifies the working volume and exposure of a surgical corridor.²⁰ The aim was to provide objective and quantitative data on the most commonly used surgical approaches to the clivus in terms of working space and surgical exposure.