The Role of Endoscopic Condylectomy in Endonasal Inferior Clivectomy and Extended Far Medial Approaches: Demonstration of Stereotactic CT Landmarks in Cadaveric Dissection with Clinical Correlation

Background: Exposing the inferior clivus, the tubercular and the condylar compartments through a narrow sinonasal corridor is a challenging task reserved for specifically trained endoscopic skull base surgeons and requires an excelsior knowledge of anatomy. We offer a comprehensive update on the role of endoscopic condylectomy in expanded endoscopic transclival approach, with special references to stereotactic intraoperative landmarks, that can help in the avoidance and mitigation of surgical complications.

Methods: In the current study, stepwise image-guided dissections were performed in 11 colored latex-injected human heads and morphometric measurements on the inferior clival region were performed verified by two independent observers. The greatest area of neurosurgical exposure was defined as the quadrangular area bounded by the most lateral accessible point at the lacerum level and at the level of the anterior arch of C1, bilaterally. The angle of attack was calculated at the level of the hypoglossal nerve and glossopharyngeal nerve. All these data points were verified by stereotactic scan thin-slice CT images.

Results: The expanded endoscopic techniques involve a deep endonasal corridor (100.1 mm ± 8.1 mm) and provide a valuable area of surgical exposure of the lower clivus (677 ± 158 mm²). The narrowest transverse length of the ventral foramen magnum (anterior intercondylar distance) was 19.1 m ± 1.51 mm, with an average gain of 6 mm, making it ∼25.5 mm ± 1.64 mm after bilateral transcondylar approach. The transverse length measured from either medial side of the ICA at the lacerum level representing the superolateral limit of the exposure was 22.8 mm ± 2.53 mm, and the mean lower clivus exposure from the floor of the sphenoid sinus to the anterior arch of C1 was 31.1 mm ± 2.04 mm. The stereotactic intraoperative landmarks were also studied by two independent observers and we have elucidated some cardinal signs for ensuring surgical safety: for example, the correlation between the radiological landmark such as the “American eagle” beak and the endoscopic landmark offered by the supracondylar groove.

Conclusion: We have demonstrated stepwise and meticulous utilization of intraoperative stereotactic CT landmarks in endonasal inferior clival surgery such as the eustachian tube, lateral pharyngeal tubercle, supracondylar groove, hypoglossal canal, and the occipital condyle. The additional area of surgical exposure obtained by bilateral endoscopic condylectomy has been demonstrated with the help of CT-guided stereotaxic in silicon injected cadavers. Customization of each anteromedial skull base lesion is hence mandated for EEA, especially in the hypoglossal canal and jugular foramen regions.