The Role of Endoscopic Endonasal Approach to the Axis Combined with Inferior Clivectomy and Extended Far Medial Approaches: Correlation of Morphometric Data with Stereotactic CT Landmarks in Cadaveric Dissection

Background: The inferior clival and CCJ region is an anatomically complex and difficult-to-access area and endoscopic skull base surgeons would require detailed knowledge of the surgical anatomy and nuances while performing lower clivectomy with further caudal extension to involve C2 body/dens.

Methods: In the current study, stepwise image-guided dissections were performed in eleven colored latex-injected human heads. Morphometric measurements on the ventral foramen magnum, depth of the corridor, surgical exposure and the surgical freedom were verified by stereotactic CT scan thin-slice images. We describe an expanded endonasal transclival transodontoid approach to the C2 vertebra, highlighting the surgical key points with a stepwise image-guided cadaveric dissection to enhance surgical safety. The authors have performed a comprehensive literature review pertinent to the indications, limitations, outcomes along with technical pearls and pitfalls to avoid complications. Special attention is given to the endoscopic visualization of the landmarks on the posterior nasopharyngeal region.

Results: The bony depression of the occipital condyle labeled as the supracondylar groove was a reliable external reference to locate the hypoglossal canal and bilateral condyles which articulates with the lateral masses of the atlas. To approach the axis, drilling the anterior arch of C1 in between the medial borders of the lateral masses, to avoid injury to the vertebral artery situated lateral to the lateral masses at the C1–C2 level. We observed that dissecting in between the Eustachian tubes using the midpoint of the posterior pharyngeal wall as the guiding landmark will reduce the risk of carotid injury as the parapharyngeal ICA often runs posterolaterally. The maximum diameter corresponding to the safe bony drilling area on the anterior arch of C1 presented an average of 17.5 ± 1.6 mm. The widest odontoid diameter, the thickness, and the height (measured from the body of C2 up to the tip of the odontoid process) was an average of 10.1 ± 1.05 mm, 10.04 ± 1.05 mm and 14.3 ± 2.4 mm, respectively. The depth of the nasal corridor measured from the anterior nasal spine to the posterior aspect of C2 along the plane of the hard palate was 96.7 ± 7.6 mm.

Conclusion: The endoscopic endonasal approach to the craniocervical junction uses a minimally invasive endonasal route instead of the traditional transoral approach, reducing morbidity and complications such as dysphagia, phonation dysfunction, and pharyngeal dehiscence. A stepwise procedure and deep knowledge of the anatomical landmarks are essential for complication avoidance.