An unusual course of the vertebral artery posterior to the nerve root in the inter-transverse space: a cadaveric study

BACKGROUND The V2 segment of the vertebral artery is very vulnerable to injury during cervical spine surgery. The incidence of vertebral artery injury during anterior cervical spine procedures is reported to be 0.22-2.77 %. This is partially due to its variable course while running in the transverse foramens of the cervical vertebrae. CASE PRESENTATION The course of the vertebral artery in the dissected cadaver of a 79 year old female is presented. Dissection of the left vertebral artery showed that the 5(th) nerve root passes in front of the vertebral artery in the 4(th) intertransverse space. Further exploration showed that although vertebral artery at first passed at the back of the nerve root it curved downwards again and after passing underneath the 5(th) nerve root entered the 4(th) vertebral body. After making a loop in the left half of the vertebrae, vertebral artery ran anterior to the nerve root and after entering the 4(th) transverse foramen showed up in the 3(rd) intertransverse space. The shortest distance of the vertebral artery to the midline at the 4(th) vertebrae level was 4.78 mm. CONCLUSIONS To our knowledge this case is the first report of a nerve root lying anterior to the vertebral artery in the intertransverse space of the cervical spine. Additionally vertebral artery has never been reported to be so close to the midline. This report signifies the importance of obtaining MRI or contrast enhanced CT scan prior to any cervical spine surgery in the vicinity of the vertebral artery including corpectomies and also careful approach to the intertransverse space during the operation.