Entrance and origin of the extracranial vertebral artery found on computed tomography angiography.

To investigated morphological variability of vertebral artery (VA) origin and its entrance level into cervical transverse foramina by computed tomography angiography (CTA). To retrospectively investigated CTA of 223 subjects (446 VA courses). Investigated were origin of the VA and its level of entrance into vertebral transverse foramen with notification of the sex and side of variation. The VA entered the C6 transverse process in 91.70% of specimens (409 out of 446 VA courses). Abnormal entrance of VA was observed in 8.30% of specimens (37 VA courses), with the level of entrance into the C3, C4, C5, or C7 transverse foramen at 0.22%, 2.47%, 4.71% and 0.90% respectively. Comparably, the overall variability of abnormal origin of VA was 1.57% (7 out of 466 VA courses), in which the left vertebral arteries all arose from aortic arch. The variation rate of vertebral entrance rose up to 50% in abnormal origin subgroup. When comparing subgroups of subjects with normal and abnormal origin, there was significance difference in the frequency of entrance variation in the level of transverse foramen (p < 0.001). Abnormal entrance and origin of VA were observed in 8.30% and 1.57% of VA courses, which can be accurately appeared by CTA. Regarding to the subgroups of abnormal origin, the frequency of entrance variation was significantly increased in the level of transverse foramen compared to that of normal origin.