How Low Can You Go? Expansion of the Nasopalatine Angle through Palatal Drill-Out

Background: The nasopalatine line (NPL) and nasopalatine angle (NPA) estimate the potential caudal exposure of an endoscopic endonasal approach (EEA) to the craniovertebral junction/cervical spine. Augmentation of this angle has been described by retraction of the soft palate or via palatal split. However, these techniques offer minimal improvement and may cause significant postoperative morbidity including dysphagia and/or velopharyngeal insufficiency, respectively. The primary limitation of EEAs to the craniovertebral junction/cervical spine is the degree of caudal exposure. This project evaluates the impact of the endonasal removal of the posterior portion of the horizontal segment of the palatine bone to increase caudal exposure.

Objectives: To evaluate if removal of the posterior portion of the horizontal segment of the palatine bone with concurrent posteroinferior septal window increases caudal access to the craniovertebral junction/cervical spine.

Study Design: Anatomic cadaveric study.

Methods: CT scans were performed on three fresh-frozen cadaveric heads using a rigid suction to radiographically demonstrate the NPL and identify the caudal limit of a potential EEA. The posterior portion of the horizontal segment of the palatine bone was then removed using a high-speed drill and scans were repeated to assess the change in the NPL and the associated new potential caudal limit. Of note, NPAs were calculated using both the preoperative and postoperative NPLs.

Results: The average initial NPA was 17 ± 6 degrees which corresponded to access at 14 ± 5 mm below the caudal edge of the clivus. On average 20.2 mm of the posterior portion of the horizontal segment of the palatine bone was removed resulting in an increase of the NPA by 9 ± 4 degrees. This increased our caudal exposure of the spine to 33 ± 15 mm below the caudal edge of the clivus, corresponding to an increase in caudal access by 18 ± 11 mm. Anatomically, in relation to the odontoid process of C2, the procedure increased exposure from the tip/upper third to the base of the odontoid process/body of C2.

Conclusion: Removal of the posterior portion of the horizontal segment of the palatine bone allows for expanded caudal access to the craniovertebral junction/cervical spine via an EEA. Further studies will be done to clarify the extent of postoperative morbidity and to determine the intraoperative improvement that is obtained. This approach represents another tool in the endoscopic skull base surgeon’s armamentarium.

No conflict of interest has been declared by the author(s).