Endoscopic Total Odontoidectomy with Preservation of C1 Anterior Arch through the Contralateral Nasofrontal Trephination Technique: A Cadaveric Study with Quantitative Analysis

Background: Endoscopic endonasal odontoidectomy represents a significant advancement in the realm of minimally invasive spine surgery, offering an alternative to the traditional transoral approach for resection of the odontoid process and anterior decompression. The corridor afforded by the endoscopic endonasal approach (EEA) to the odontoid and craniovertebral junction (CVJ) reduces the risk of velopharyngeal insufficiency and facilitates faster recovery by avoiding postoperative wound, airway, and swallowing complications or sequelae. An EEA odontoidectomy usually requires drilling of the anterior arch of the C1 vertebra, which entails disruption of the CVJ ligaments affecting joint stability. Existing literature posits the nasoaxial line as a determinant for the caudal limitation of an endonasal approach. This study demonstrates the viability of a novel technique to enhance the access afforded by the endonasal corridor to the CVJ, eliminating this limitation. In addition, the precision of stability-sparing odontoidectomy via the EEA + CNT corridor is improved as the technique enables complete preservation of the C1 anterior arch and the transverse portion of the cruciate ligament.

Method: EEA and EEA + contralateral nasofrontal trephination (CNT) approaches for exposure to the odontoid process and the CVJ were carried out in 15 latex-injected cadaveric specimens. Endoscopic odontoidectomy was performed with preservation of the C1 anterior arch and the transverse ligament of the atlas using both approaches. The angle of attack on the sagittal plane, inferior reach advantage, volume of surgical freedom, and area of deep exposure through both approaches were quantified with neuronavigation system and adjuvant software. After software analysis, all data were compared statistically.

Results: EEA + CNT provided a superior area of target exposure and volume of surgical freedom around the odontoid process and the CVJ. Only the tip of the odontoid could be drilled endonasally while total drilling of the odontoid process till its base could be carried out through the CNT port in all 15 cadavers sparing the C1 anterior arch and the transverse portion of the cruciate ligament. The CNT demonstrated an increased inferior reach advantage of 35 mm and a wider sagittal angle of attack of 48.33 degrees compared to the EEA (17.32 degrees). The area of exposure of the CNT around the odontoid (542.98 ± 167.32 mm²) was significantly greater than the EEA (378.54 ± 109.66 mm²). Moreover, the volume of surgical freedom of the CNT was 2,683.66 ± 309.44 mm³, while the EEA showed a surgical freedom of 1,375 ± 177.42 mm³. All the differences were statistically significant between the two groups (p < 0.001).

Conclusion: The EEA + CNT technique has demonstrated superior access characteristics to the odontoid and CVJ region with acceptable approach-related morbidity. For select midline lesions in this territory, an EEA + CNT corridor may serve as a viable alternative for minimally invasive extirpation.

Publication History

Article published online:
07 February 2025