Incidence of vertebral artery of aortic arch origin, its level of entry into transverse foramen, length, diameter and clinical significance.

The aim of this study was to show the incidence of vertebral artery of aortic arch origin, its level of entry into transverse foramen, including extra- and intracranial morphometry, and clinical significance. A total of 266 embalmed cadavers were studied. We found 14 left vertebral arteries (5.3%) emerging from aortic arch. Most of the left vertebral arteries of aortic arch origin (78.6%) entered the fifth cervical transverse foramina, whereas most of the vertebral arteries of subclavian origin (94.7% left and 99.2% right) entered the sixth cervical transverse foramina. Their average prevertebral length was 8.24 ± 1.09 cm ,which was about twice as long as the right vertebral artery (3.88 ± 1.14 cm). The average outer diameters of the prevertebral part and ensuing intracranial part of the left vertebral artery of aortic arch origin were 4.36 ± 0.93 and 3.62 ± 0.62 mm, respectively. The mean corresponding diameters of the vertebral artery of subclavian origin were 5.06 ± 1.04 and 3.87 ± 0.83 mm, respectively. All of the vertebral arteries decreased significantly in size after entering the cranial cavity. The reduction in caliber of the intracranial part of the vertebral artery compared with the prevertebral part of its own vessel has never been reported elsewhere. Knowledge of such anatomical variations is important in interpreting CT angiography, anterior cervical decompression and aortic arch surgery to prevent iatrogenic injury of the vertebral artery.