Neurovascular Anatomy II: The Spinal Cord Blood Supply
The spinal and radicular arteries supply blood to the spinal cord at all levels, however different spinal cord segments are preferentially supplied by one or other sets of arteries. The cervical spinal cord is supplied by both the vertebral and radicular arteries (the ascending cervical artery). The thoracic, lumbar, and sacral segments are supplied primarily by the radicular arteries (the intercostal and lumbar arteries) but fewer segmental radicular arteries supply the individual rostral thoracic segments. The sources of arterial blood to the cord can be traced to the segmental vessels of the cervical and vertebral arteris of the neck, thorax and abdomen (intercostal and lumbar branches of the thoracic and abdominal aorta) cervical and sacral arteries of the pelvis.
The systemic circulation of arterial blood supplies blood to the spinal cord by one anterior and two posterolateral vessels that run along the length of the cord. An irregular plexus of segmentally arranged vessels encircles the spinal cord and interconnects the major vessels. There is an anterior and posterior supply, the anterior spinal artery (anterior supply) is a single vessel lying in the ventral median fissure. It arises from a pair of small branches of the vertebral arteries that fuse along the caudal medulla and descend along the cervical spinal cord.
A series of six to eight ventral radicular arteries arising form the intercostal, lumbar, and sacral arteries connect with the anterior spinal artery at various levels along the length of the spinal cord. The largest of these radicular arteries enters at the low thoracic or upper lumbar region. Because of this uneven blood supply, the spinal cord is most vulnerable to ischemia at the mid thoracic and upper lumbar levels.
The anterior surface of the spinal cord is supplied by the anterior spinal artery and its branches. It is considered to be the longest identifiable artery in the body; its continuity is maintained by a series of segmental vessels joining it at several levels bilaterally. It is formed rostrally by two arteries that arise from the intracranial portion of the vertebral arteries. These paired spinal arteries descend to merge at the vertebral level of C3 to form the unpaired anterior spinal artery. As this vessel descends within the anterior median fissure, it is variably supplied by a series of radicular arteries from segmental vessels, such as spinal branches of thyro-cervical, costo-cervical, intercostal and lumbar arteries. The radicular arteries approach the spinal cord from the sides, riding over the spinal roots. Branches of the anterior spinal artery penetrate into the gray matter via the various sulci.
The posterior spinal arteries (posterior supply) are paired structures that run along the posterolateral aspect of the cord near the dorsal roots. They receive contributions from the posterior radicular arteries and supply the dorsal funiculus and dorsal gray horns. The paired posterior spinal arteries also arise from the vertebral arteries; they descend near the dorsal root entry zones. They receive posterior branches of the radicular arteries mentioned above. The spinal cord is cradled in a loosely woven network of vessels, some of which encircle the cord. In this way blood vessels reach the gray and white matter of the spinal cord.The sources of arterial blood to the cord can be traced to the segmental vessels of the thorax and abdomen (intercostal and lumbar branches of the thoracic and abdominal aorta) cervical and vertebral arteries of the neck, and sacral arteries of the pelvis.
Axons traveling to the periphery are gathered into bundles or fascicles that have a connective tissue covering. Within this covering, along the entire course of the nerve, is a rich and highly anastomotic plexus of small arterioles derived from the branches of the major extremity vessels. This dense anastomosis renders the peripheral nerve relatively immune to ischemic vascular disease. Such abnormality, when noted in the peripheral neural structures is usually associated with either direct compression of a nerve or with multiple segmental vascular lesions from small vessel arterial disease.
Spinal Cord blood is drained in part, by an extensive venous plexus associated with the vertebral column. The veins of the spinal cord tend to follow the arteries, except that they are more numerous and tend to merge into complex networks. The spinal cord blood supply is drained by an extensive, anastomotic venous plexus within the vertebral column surrounding the dural sac. Veins drain outward along both the dorsal and ventral roots into this plexus, which has numerous connections with the veins of the thoracic abdominal and pelvic cavities. The spinal veins, like their arterial counterparts, consist of a single anterior spinal vein and paired posterior spinal veins interconnected by a venous vasocorona. These veins are drained by anterior and posterior radicular veins, which are the tributaries of the internal vertebral venous plexus. This plexus of veins, located in the epidural space, runs the length of the spinal cord. Between each pair of vertebrae, intervertebral veins drain into segmental veins as well as the external vertebral venous plexus. In the neck, the radicular veins join the vertebral veins.
What happens when the shit hits the fan
All neural structures must receive adequate arterial blood supply in order to sustain life and to maintain their integrity. When spinal cord segments are supplied by a single artery, they are particularly susceptible to injury after arterial occlusion. For example, individual rostral thoracic segments are supplied by fewer radicular arteries than are more caudal segments. When a radicular artery that serves the rostral thoracic segments becomes occluded, serious damage is more likely to occur because there is no backup suppply for perfusion of oxygenated blood. Interruption of the blood supply to critical areas of the spinal cord can produce sensory and motor control impairments similar to those produced by traumatic mechanical injury, like an automobile accident.Segments that receive a redundant (or collateral) blood supply tend to fare better following single vessel occlusion.