The spinal cord, a bundle of nerves extending from the brainstem, transmits signals throughout the body. This delicate structure requires a constant supply of oxygen and nutrients, delivered through a sophisticated network of blood vessels. This system, known as the spinal cord vascular supply, ensures the healthy functioning of the spinal cord. Any disruption can have significant consequences, highlighting the importance of understanding its anatomy.
The Spinal Cord’s Arterial Network
The spinal cord receives its arterial blood supply from longitudinal and segmental arteries. Three main longitudinal arteries extend along the spinal cord: a single anterior spinal artery and two posterior spinal arteries. These are reinforced by numerous segmental medullary arteries, which provide additional blood flow.
The anterior spinal artery, a sizable vessel formed by branches from the vertebral arteries, travels along the anterior median fissure of the spinal cord. This artery is responsible for supplying the anterior two-thirds of the spinal cord, including the anterior gray column, lateral gray column, central gray matter, and the anterior and lateral funiculi. Its diameter varies, being notably larger in the cervical and lumbar regions compared to the mid-thoracic sections.
The paired posterior spinal arteries supply the posterior one-third of the spinal cord. These arteries are small and often discontinuous, running along the posterolateral sulcus near the dorsal nerve roots. They primarily originate from the vertebral arteries in about 25% of individuals or the posterior inferior cerebellar artery in roughly 75% of cases. These vessels provide blood to the posterior columns, dorsal gray matter, and dorsal sensory columns.
Radicular arteries reinforce the main longitudinal arteries. These arteries arise from spinal branches of various larger vessels, including vertebral, ascending cervical, deep cervical, intercostal, lumbar, and sacral arteries. They course alongside spinal nerve roots and can pierce the dura mater to directly supply the spinal cord.
A significant reinforcing artery is the Great Anterior Medullary Artery of Adamkiewicz (AKA). This artery is the dominant segmental feeding vessel to the lower spinal cord, supplying the anterior spinal artery in the lower thoracic, lumbar, and sacral segments. It originates from the left side of the aorta, usually from a posterior intercostal or lumbar artery, between vertebral levels T8 and L2. The AKA takes a characteristic “hairpin turn” before joining the anterior spinal artery.
The spinal cord’s arterial network features arterial anastomoses and collateral circulation. The anterior and posterior spinal arteries are interconnected by a pial plexus called the arterial vasocorona, which encircles the cord. This network of interconnected vessels, including an epidural arterial network, can provide compensatory blood flow if some direct inputs are compromised. This helps ensure a consistent blood supply, even with partial blockage or damage.
How Blood Drains from the Spinal Cord
The venous drainage of the spinal cord mirrors its arterial supply, but is more extensive and variable. Blood is collected through a system of veins that ultimately empty into larger systemic veins.
Three anterior and three posterior spinal veins run longitudinally along the spinal cord’s surface. These veins form an interconnected plexus. The anterior spinal veins run alongside the anterior spinal artery within the anterior median fissure, and can be paired or single.
These longitudinal spinal veins receive blood from smaller radial and sulcal veins that drain the spinal cord’s interior. Blood then flows into radicular veins, which accompany the spinal nerve roots, and empty into larger venous plexuses surrounding the vertebral column.
The primary receiving plexuses are the internal and external vertebral venous plexuses. The internal vertebral venous plexuses lie within the epidural space, while the external plexuses surround the vertebral column. These plexuses are highly anastomotic and communicate freely via intervertebral veins. Their valveless nature allows for bidirectional blood flow, which can have implications for the spread of infections or cancer cells. Ultimately, these plexuses connect to systemic veins, such as the azygos, hemiazygos, lumbar, and deep cervical veins, which return blood to the heart.
Why Spinal Cord Blood Supply Matters
The spinal cord’s vascular supply is susceptible to disruption, leading to serious neurological consequences. Certain areas are particularly vulnerable to reduced blood flow, known as ischemia. These “watershed areas” are typically located where different arterial supplies meet and collateral circulation may be less robust. A longitudinal watershed zone is commonly found in the mid-thoracic spinal cord, often between T4 and T6. A transverse watershed zone can exist in the central and peripheral gray matter, where higher metabolic demand and reduced blood supply combine to increase vulnerability.
Compromised blood flow to the spinal cord can result in spinal cord ischemia or infarction, often referred to as a “spinal stroke.” This condition involves the death of spinal cord tissue due to insufficient blood supply. Spinal cord infarction occurs less frequently than cerebral infarction but can lead to significant disability.
Symptoms of spinal cord ischemia appear suddenly, within minutes or hours. Patients experience sudden, severe back pain, often radiating down the legs. This is accompanied by rapidly progressive weakness or paralysis in the limbs.
Sensory loss, particularly for pain and temperature, is common, while touch and proprioception may be relatively spared. Incontinence can also occur. Upper cervical spinal cord infarction can lead to breathing difficulties or respiratory failure.
Several scenarios and conditions can lead to compromised spinal cord blood supply. A common cause is injury to an extravertebral feeder artery or the aorta itself, which can occur due to atherosclerosis, aortic dissection, or clamping of the aorta during certain surgeries. For example, thoracoabdominal aortic aneurysm repairs carry a risk of spinal cord ischemia due to temporary interruption of blood flow.
Severe hypotension (low blood pressure) and trauma can also reduce blood flow to the point of causing ischemia. Conditions like thrombosis (blood clotting disorders) and specific arterial blockages, such as those affecting the artery of Adamkiewicz, can also lead to spinal cord infarction. Maintaining adequate blood pressure and oxygenation is important for spinal cord health.