Spinal anatomy: Anterior spinal artery syndrome

The spinal cord receives blood supply from two posterior arteries (25%) and one anterior spinal artery (75%). The posterior arteries supply the sensory tracts in the spinal cord and receive flow from posterior and inferior cerebellar arteries, the vertebral arteries, and the posterior radicular arteries. The anterior artery supplies the motor tracts and is formed by the fusion vertebral arteries and receives reinforcement of blood supply from 6 to 8 radicular arteries, the artery of Adamkiewicz is the most important of these. This leaves multiple areas of the cord vulnerable to watershed ischemia, particularly during aortic occlusion or hypotension. Anterior spinal artery syndrome manifests as flaccid paralysis of the lower extremities and bowel and bladder dysfunction with sparing of proprioception and sensation, due to the selective ischemia to the anterior portion of the cord. In vascular surgery, the risk of paralysis related to ASAS ranges from 0.2% in elective infra-renal AAA repair, 8% in elective thoracic aneurysm repair and 40% in the setting of dissection or rupture involving the thoracic cord. The duration of cord clamping is a key determinant of the risk of paraplegia.