Vertical Levels of the Occipital Artery Origin.

The occipital artery (OA) is a posterior branch of the external carotid artery (ECA). The origin of the OA is commonly referred to a single landmark. We hypothesized that the origin of the OA could be variable as referred to the hyoid bone and the gonial angle. We thus aimed at patterning the vertical topographic possibilities of the OA origin. One hundred archived computed tomography angiograms were randomly selected, inclusion and exclusion criteria were applied, and 90 files were kept (53 males, 37 females). The cases were documented bilaterally for different levels of origin of the OA origin: type 1-infrahyoid; type 2-hyoid; 3-infragonial; 4-gonial; 5-supragonial; 6-origin from the internal carotid artery (ICA). The incidence of unilateral types in the 180 OAs was: type 1-1.11%, type 2-5.56%, type 3-40.56%, type 4-28.33%, type 5-23.33% and type 6, ICA origin of the OA-1.11%. There was found a significant association between the location of the left and right origins of the OAs (Pearson Chi2 = 59.18, < 0.001), which suggests the presence of a strong symmetry of the origins. Bilateral symmetry of the vertical types of the OA origin was observed in 56.67% of cases; in 43.33% there was bilateral asymmetry. The ICA origin of the OA is an extremely rare variant. For surgical planning or prior to endovascular approaches the topography of the OA origin should be carefully documented, as it may be located from an infrahyoid to a supragonial level.