Blood Supply of the Spinal Cord
The vertebral arteries are the main source of blood to the spinal cord. However, the following arteries branch from the vertebral arteries to directly supply the spinal cord itself:
- one anterior spinal artery
- two posterior spinal arteries
- anterior and posterior radicular arteries
- arterial vasocorona (anastomose between the spinal arteries)
The anterior and two posterior spinal arteries are direct branches of the two vertebral arteries which merge rostrally to form a single artery - the basilar artery of the Circulus arteriosus (Circle of Willis).
Thus, the vertebral arteries are very important, as they serve as the primary source of blood to the brain and the spinal cord.
Similarly, the radicular arteries take origin from spinal branches of the vertebral arteries and spinal branches of ascending cervical arteries, deep cervical arteries, intercostal arteries, lumbar arteries and sacral arteries.
To understand the arterial distribution of the spinal cord, a good knowledge of the gross and internal structures of the spinal cord is encouraged.
The radicular arteries represent highly important contributions that reinforce the anterior and posterior spinal arteries. At a particular stage in neurulation and further embryonic development, every segment of the spinal cord receives a radicular vessel on both sides of the midline.
These vessels enter through the intervertebral foramina as spinal arteries to penetrate the meninges and run along the nerve roots, and are derived from various parent vessels depending on the level – vertebral, costocervical, posterior intercostal, lumbar, lateral sacral.
As fetal growth proceeds, most of the radicular arteries disappear. Those that remain form anastomoses with the anterior and two posterior spinal arteries. These communicating radicular arteries are commonly called booster or feeder vessels. This is because blood from the vertebral arteries to the anterior and posterior spinal arteries cannot sustain the spinal cord beyond the level of the cervical segments, and the arterial supply to a considerable length of the spinal cord depends on the radicular supply.
Course and Distribution
The anterior and posterior radicular arteries arise from spinal branches of the vertebral, ascending cervical, deep cervical, intercostal, lumbar and sacral arteries. These radicular arteries are arranged radially, and course alongside the dorsal and ventral roots of spinal nerves to pierce and supply blood to the spinal cord. Some of the very small radicular arteries end by supplying those spinal nerve roots. A few of those which are larger, join the anterior and posterior spinal arteries and contribute blood to them.
The largest of the anterior radicular branches usually arise from the lumbar arteries between the L1 and L2 vertebrae. This largest anterior radicular branch is called the artery of Adamkiewicz or anterior radicularis magna (ARM) or arteria radicularis magna.
Thus the anterior and posterior radicular arteries supply the:
- spinal cord (along its entire length)
- spinal nerve roots
- anterior and posterior spinal arteries
The spinal cord is covered along its length within the vertebral canal (spinal canal), by spinal meninges. The pia mater of spinal meninges is highly vascularized and has an arterial plexus called the arterial vasocorona. This arterial network also sends branches into the spinal cord.
The spinal cord receives blood from three longitudinal arterial channels that extend along the length of the spinal cord. These longitudinal arteries are:
- the anterior spinal artery, which runs along the anterior median fissure
- two posterior spinal arteries, which run (one on each side of the midline) along the posterolateral sulcus (i.e., along the line of attachment of the dorsal nerve roots).
Although the anterior and posterior spinal arteries are longitudinal and extend the length of the spinal cord, blood to these spinal arteries (flowing from the vertebral arteries) reaches only up to the cervical segments of the spinal cord. Lower down, the spinal arteries receive blood through radicular arteries. Thus, the radicular arteries are commonly referred to as feeder arteries of the spinal cord.
Arterial distribution of the spinal cord is more readily visualised on a transverse section of the cord. The greater part of the cross sectional area of the spinal cord is supplied by branches of the anterior spinal artery.
The anterior spinal artery gives off branches, some of which enter the cord through the anterior median fissure (or anterior median sulcus) and are, therefore, called sulcal branches of the anterior spinal artery. The anterior spinal artery and its branches supply:
- the anterior grey column of the spinal cord (lamina VIII & IX)
- the lateral grey column of the spinal cord (lamina VII)
- the central grey matter (lamina X)
- the anterior funiculus (white matter)
- the lateral funiculus
- the anterior portion of the posterior grey matter
The two posterior spinal arteries and the pial arterial plexus (arterial vasocorona) supply the:
- posterior grey column (including lamina I – VI)
- posterior funiculus
Thrombosis (formation of blood clot) in the anterior spinal artery produces a characteristic syndrome. The territory of supply/areas affected includes the corticospinal tracts and the spinothalamic tracts.
Thrombosis to vessels supplying the corticospinal tracts leads to an upper motor neuron paralysis below the level of lesion (level in the artery where the clot is located). Thrombosis to the arterial supply of the spinothalamic tracts lead to loss of sensations of pain and temperature below the level of lesion. Thrombosis in the posterior spinal arteries affect the posterior column tracts and thus leads to loss of touch and conscious proprioceptive sensations.