Anatomical Relationships of Internal Carotid Artery with Posterior Pharyngeal Wall and Upper Cervical Spine: Analysis of 238 Computed Tomography Angiograms.

Objective: To evaluate internal carotid artery's (ICA) anatomical relationships with atlantoaxial joints and posterior pharyngeal wall and to illustrate ICA injury risk during transoral procedures to the upper cervical spine.

Methods: Cervical spine computed tomography angiography of 238 patients was retrospectively evaluated. Each ICA was classified into 1 of 3 zones: areas medial (Zone 1), anterior (Zone 2), or lateral (Zone 3) to the atlantoaxial joint. For an ICA in Zone 1, the shortest distances to the posterior pharyngeal wall and midsagittal plane were measured. For an ICA in Zone 2, the closest distances to the midsagittal plane and anterior cortex of the C1-2 complex were measured.

Results: Fifteen ICAs in Zone 1 were found in 12 (5%) patients, with 3 female patients having bilateral ICAs medial to the atlantoaxial joint. The incidence of ICA in Zone 1 was higher in females than in males. In cases of ICAs in Zone 2, the ICAs were close to the anterior cortex of the C1-2 complex, with the shortest distance being 2.6 ± 1.5 mm. A total of 39.9% of patients had bilateral ICAs in Zone 3.

Conclusions: Transoral surgeries in the upper cervical spine carry potential ICA injury risk. They should be carefully deliberated in patients whose ICAs are in Zone 1. In cases of ICAs in Zone 2, meticulous subperiosteal stripping and gentle traction should be performed on the posterior pharyngeal wall. Preoperative identification of the course of ICAs is mandatory in patients undergoing transoral surgeries in the upper cervical spine.