Anatomical relationship between carotid artery and styloid and hyoid bones in patients showing unintended head rotation on CTA.

Styloid process length and styloid/hyoid bone proximity to the internal carotid artery (ICA) have been implicated in certain carotid pathologies (e.g. carotid artery dissection). Neck movement or trauma may contribute to some of these carotid pathologies. Styloid/hyoid bone to ICA distances have never been systematically analyzed in regard to head rotation and head flexion-extension. We studied axial slices on computed tomography angiograms of 103 nondissection patients showing > 1° head rotation. We measured the distance between ICA and the hyoid bone (HICA) and the closest point and the tip of the styloid bone (SCICA and STICA, respectively), the length of the styloid, and the angle of head rotation and head flexion-extension. STICA distances were significantly smaller on the right as compared to the left side in both the right and the left rotating patient groups (right STICA, 4.4 mm for the right rotating group and 6.4 mm for the left rotating group, p = 0.0091; left STICA, 5.1 mm for the right rotating group and 6.9 for the left rotating group, p = 0.034). No significant differences were observed for SCICA and HICA distances between right and left rotating groups, and head flexion-extension did not altered significantly SCICA, STICA, or HICA distances. Both right- and left-sided head rotation seems to be associated with decreased right-sided and increased the left-sided styloid tip to internal carotid artery distances. This has to be studied and confirmed in single patient analyses using more severe head rotation and flexion-extension angles.