Morphological expression of the anterior spinal artery and the intracranial segment of the vertebral artery: a direct anatomic study.

Given its importance for clinical diagnosis and management, the purpose of this study was to determine the morphological expression of the intracranial segment of both vertebral and spinal arteries. Ninety-five fresh cadaveric specimens autopsied at the Instituto de Medicina Legal of Bucaramanga (Colombia) were perfused with polyester resins at the vertebrobasilar vascular bed, by canalizing the proximal segment of the internal carotids and vertebral arteries. The intracranial segment of the vertebral arteries (VA) had a length of 33.2±5.2 mm and a caliber of 3.03±0.81 mm. The left vertebral artery had a caliber of 3.12±0.85 mm, this being greater than the caliber of the right artery in 59.6% of the cases. The VA junction was seen at the level of the ponto-medullary sulcus in 44.2%, above this level in 30.5%, and below it in 25.3%. The distance from the origin of the anterior spinal branches (ASBs) to the VA junction was 7.34±2.71 mm, with a greater distance corresponding to the right ASBs, a difference that did not reach statistical significance (p=0.32). The anterior spinal arteries (ASA) had a bilateral origin in 65.3% of the cases, with the caliber being balanced in 37 (39%) and dominant at the right side in 15.8%. A right unilateral origin of the ASA was observed in 13.7% and a left unilateral origin in 9.5% of the specimens. There is disagreement in the literature as to the level of the junction of the two vertebral arteries. The unilateral origin of the spinal arteries is more frequent than most prior studies have indicated.