Extending the Inferior Limit of Endoscopic Endonasal Surgery to the Cervical Spine Utilizing an Endoscopic Endonasal Posterior Palatectomy

Introduction: The endoscopic endonasal approach (EEA) has become an increasingly utilized means of addressing pathology at the craniovertebral junction (CVJ) as an alternative to the transoral-transpharyngeal approach (TOA). Although the EEA may offer decreased morbidity compared with the TOA, it is physically limited in its caudal working exposure by the nasal bone anteriorly and the hard palate posteriorly and thus offers restricted caudal access compared with the TOA.

Objective: We hypothesized that performing an endoscopic endonasal partial posterior palatectomy would extend the inferior limit of the EEA caudally, thereby, increasing the working corridor to the upper cervical spine.

Methods: A total of 10 formalin-fixed cadaveric specimens underwent high-resolution computed tomography (CT) scanning for registration to a stereotactic navigation device. These were assigned to one of two groups: one utilizing an angled drill and one utilizing a straight drill to perform bony resection. Using the navigation probe, the caudal-most limit of access with the assigned drill system to the anterior aspect of the vertebral bodies (AVB) and posterior aspect of the vertebral bodies (PVB) in the upper cervical spine were recorded. Then, the posterior hard palate was resected with the assigned drill from the midline maxillary crest to approximately halfway between midline and the medial maxillary sinus wall unilaterally on the side of the drill. This was done in 0.5 mm incremental resections with basion-to-AVB (b-AVB) and basion-to-PVB (b-PVB) measurements taken immediately afterward until no further caudal exposure was gained. The maximal gain in the b-AVB and b-PVB line was recorded for each specimen and averaged within each group of five specimens.

Results: The average prepalatectomy b-AVB and b-PVB distances accessible to the straight drill were 18.74 and 20.96 mm respectively, and the postpalatectomy b-AVB and b-PVB distances were 29.88 and 36.24 mm. For the straight drill, the average caudal exposure gained with palatectomy was 11.14 mm to the AVB and 15.28 mm to the PVB. The average prepalatectomy b-AVB and b-PVB distances accessible to the angled drill were 28.84 and 38.04 mm, respectively, and the postpalatectomy b-AVB and b-PVB distances were 44.64 and 51.14 mm. For the angled drill, the average caudal exposure gained with palatectomy was 15.8 mm to the AVB and 13.1 mm to the PVB.

Conclusion: Posterior palatectomy improved caudal access substantially when using both the straight and angled drills. Angled drills provided substantially improved caudal access via EEA compared with straight drills both with and without palatectomy. On the basis of our measurements, the additional caudal access gained for the straight drill was approximately equal to the b-AVB and b-PVB available to the angled drill without palatectomy.