Segmental Spinal Arteries

The segmental spinal arteries are arterial vessels that approach the vertebral canal at successive levels of the vertebral column and contribute to the blood supply of the vertebrae, meninges, spinal nerve roots, and spinal cord. Rather than arising from a single continuous parent artery, they originate from different regional arteries according to their location in the cervical, thoracic, lumbar, and sacral regions.^[1][2]

After entering the vertebral canal through the intervertebral foramina, their spinal branches divide into vessels supplying local structures. Some branches accompany the anterior and posterior spinal nerve roots as radicular arteries. A smaller number continue along the roots to reach the spinal cord and reinforce its longitudinal arteries. These larger vessels are termed segmental medullary arteries.

This distinction is fundamental to spinal vascular anatomy. Although arteries enter the vertebral canal at many segmental levels, not every spinal branch reaches the spinal cord, and not every radicular artery contributes to the longitudinal spinal arterial circulation.

Regional Origins

The arterial sources of spinal branches change along the vertebral column. These vessels arise from arteries that already supply the corresponding regions of the neck, thorax, abdomen, and pelvis.

Region	Important Arterial Sources
Cervical	Vertebral, ascending cervical, and deep cervical arteries
Thoracic	Posterior intercostal arteries
Lumbar	Lumbar arteries
Sacral	Primarily lateral sacral arteries and related pelvic arterial branches

The segmental pattern reflects the organization of the vertebral column and spinal nerves. Regional arteries send branches toward the intervertebral foramina, allowing blood to reach structures within the vertebral canal from multiple levels.

Entry into the Vertebral Canal

Spinal branches enter the vertebral canal through the intervertebral foramina, closely related to the spinal nerves and their roots. Once inside the canal, they participate in the supply of several different anatomical structures.

Branches may supply the vertebral bodies and arches, epidural tissues, meninges, and spinal nerve roots. Selected vessels continue farther toward the spinal cord itself.

The resulting arterial arrangement is therefore more complex than a simple series of vessels passing directly from the body wall to the cord. Each spinal branch can contribute to several local vascular territories before, in some cases, giving rise to a vessel that reaches the spinal cord.

Branches within the Vertebral Canal

After entering the vertebral canal, spinal arterial branches can be considered according to the structures they supply.

Branch Type	Principal Distribution
Vertebral branches	Vertebral bodies, arches, and associated tissues
Meningeal branches	Spinal meninges and related tissues
Anterior radicular arteries	Anterior spinal nerve roots
Posterior radicular arteries	Posterior spinal nerve roots
Segmental medullary arteries	Reach and reinforce the longitudinal arteries of the spinal cord

The terminology emphasizes destination. Radicular arteries terminate primarily in the nerve roots, whereas segmental medullary arteries extend to the spinal cord and contribute directly to its arterial circulation.^[1]

Radicular Arteries

Radicular arteries accompany the anterior and posterior roots of spinal nerves. They supply the roots, their coverings, and associated structures as the roots pass between the spinal cord and intervertebral foramina.

Anterior radicular arteries accompany anterior roots, while posterior radicular arteries accompany posterior roots. These vessels should not automatically be regarded as contributors to the spinal cord itself.

Many radicular arteries terminate before reaching the longitudinal spinal arteries. Only selected larger vessels extend sufficiently far to establish substantial connections with the anterior or posterior spinal arterial systems. Those vessels are classified as segmental medullary arteries.

Segmental Medullary Arteries

Segmental medullary arteries are the major segmental vessels that reach the spinal cord and reinforce its longitudinal arterial supply. They are fewer than the spinal nerve roots and are not present as large reinforcing vessels at every vertebral level.

They are divided according to the longitudinal arterial system they reinforce:

• Anterior segmental medullary arteries: Accompany anterior roots and reinforce the anterior spinal artery.
• Posterior segmental medullary arteries: Accompany posterior roots and reinforce the posterior spinal arteries.

The number, caliber, and levels of these arteries vary substantially among individuals. Their irregular distribution is one reason the spinal cord cannot be understood as receiving identical segmental arterial input at every level.

Relationship to the Anterior Spinal Artery

The anterior spinal artery begins superiorly from branches associated with the vertebral arteries and descends along the anterior median fissure. It supplies much of the anterior and central spinal cord.

As it descends, it receives reinforcement from anterior segmental medullary arteries. This additional inflow is essential because the longitudinal vessel alone does not provide an independent uninterrupted source of blood sufficient for the entire length of the spinal cord.

The importance of individual segmental contributions differs by region. In the lower thoracic and lumbosacral cord, one particularly large anterior segmental medullary artery commonly provides a major contribution.

Great Anterior Segmental Medullary Artery

The great anterior segmental medullary artery, commonly called the artery of Adamkiewicz, is the largest segmental medullary artery and an important source of arterial blood to the lower spinal cord.

It usually originates from a spinal branch of a posterior intercostal or lumbar artery. It most often arises on the left side and commonly enters the vertebral canal in the lower thoracic or upper lumbar region, although both its side and level are variable.^[1][2]

The artery accompanies an anterior spinal nerve root toward the spinal cord and joins the anterior spinal artery. Because it may provide a substantial proportion of the arterial inflow to the lower cord, preservation of this vessel can be important during procedures involving the thoracic and abdominal aorta.

Relationship to the Posterior Spinal Arteries

The paired posterior spinal arteries descend along the posterolateral surface of the spinal cord and predominantly supply the posterior portion of the cord.

Posterior segmental medullary arteries reinforce this longitudinal system at variable levels. They generally accompany posterior nerve roots as they approach the spinal cord.

The posterior spinal circulation typically receives multiple segmental contributions. As elsewhere in the spinal vascular system, however, their number and precise distribution vary between individuals.

Pial Arterial Network

The anterior and posterior spinal arterial systems are interconnected around the surface of the spinal cord by a pial arterial network commonly called the vasocorona.

This network surrounds the cord and distributes arterial branches to its peripheral regions. It also provides anastomotic connections between the longitudinal arteries.

Segmental medullary arteries therefore contribute to more than isolated longitudinal channels. Their blood enters an interconnected vascular system composed of the anterior spinal artery, posterior spinal arteries, pial vessels, and penetrating branches.

Arterial Supply by Region

Cervical Region

In the cervical region, spinal branches may arise from the vertebral arteries and from branches of the subclavian arterial system, particularly the ascending cervical and deep cervical arteries.

These vessels enter the vertebral canal through the cervical intervertebral foramina and contribute to the supply of the nerve roots, meninges, vertebral structures, and spinal cord.

Thoracic Region

In the thorax, spinal branches arise principally from the posterior intercostal arteries. These arteries travel in the intercostal spaces and give off spinal branches near the intervertebral foramina.

Thoracic segmental supply is clinically important because selected posterior intercostal arteries give rise to medullary vessels that contribute substantially to spinal cord perfusion.

Lumbar Region

In the lumbar region, spinal branches arise from the lumbar arteries, which originate from the posterior aspect of the abdominal aorta. Their spinal branches enter the intervertebral foramina and divide into local and neural branches.

A lumbar artery may give rise to a major segmental medullary contribution, including the artery of Adamkiewicz when that vessel originates at a lumbar level.

Sacral Region

In the sacral region, branches from the lateral sacral arteries and related pelvic vessels contribute to the vascular supply of the sacral canal, nerve roots, meninges, and surrounding structures.

The lower end of the spinal cord normally lies well above the sacrum in adults, so vessels in the sacral canal are principally related to the descending roots of the cauda equina and associated tissues rather than to the spinal cord proper.

Relationship to the Spinal Nerve Roots

The close association between segmental vessels and spinal nerve roots reflects their common route through the intervertebral foramina. After a spinal branch enters the canal, radicular vessels follow the roots toward the spinal cord.

This arrangement creates an important anatomical distinction between the vertebral level at which an artery enters the canal and the spinal cord territory to which its blood may ultimately contribute. The relationship becomes especially significant in the lower vertebral column because spinal nerve roots descend for considerable distances before reaching their exit foramina.

Segmental vascular anatomy therefore cannot be interpreted solely by matching a spinal nerve number with the same-numbered vertebra.

Relationship to the Vertebrae and Meninges

Segmental spinal branches also participate in the vascular supply of structures surrounding the spinal cord. Branches enter the vertebral bodies and posterior elements and form anastomoses with neighboring vertebral vessels.

Meningeal branches supply the dura mater and other tissues within the vertebral canal. These branches are distinct from the vessels that continue to the surface and substance of the spinal cord.

The same regional arterial source can therefore contribute simultaneously to vertebral, meningeal, radicular, and spinal cord circulation through different branches.

Anatomical Variation

Variation is a defining feature of the segmental spinal arterial system. The number of arteries that actually reach the spinal cord, their vertebral levels, their side of entry, and their relative caliber differ between individuals.

Segmental medullary arteries are not arranged as one equivalent artery for each spinal cord segment. Some levels have substantial arterial reinforcement, while other levels depend more heavily on longitudinal flow from neighboring regions.

The artery of Adamkiewicz is an important example of this variation. Although it is commonly left-sided and usually arises in the lower thoracic to upper lumbar region, its precise origin cannot be reliably predicted in an individual without vascular imaging.

Clinical Significance

The clinical importance of segmental spinal arteries comes from their role in maintaining blood flow to the spinal cord and from their close relationship to the vertebral column, nerve roots, and major regional vessels.

Aortic Surgery

Posterior intercostal and lumbar arteries arise directly from the thoracic and abdominal aorta and may give rise to important segmental medullary arteries. Procedures involving the aorta can therefore alter the arterial supply of the spinal cord.

Interruption of a major segmental contributor can reduce spinal cord perfusion, particularly when collateral pathways are insufficient. The artery of Adamkiewicz receives particular attention during thoracic and thoracoabdominal aortic procedures because of its important contribution to the lower spinal cord.

Spinal Surgery

Segmental vessels are also relevant during surgery involving the vertebral bodies, pedicles, intervertebral foramina, and paravertebral tissues. A vessel entering a foramen may ultimately supply a nerve root, the meninges, or the spinal cord.

Because the major medullary arteries are variable, their presence cannot be inferred reliably from external landmarks alone. Vascular imaging may be used when identification of critical arterial contributors is necessary for procedural planning.

Spinal Cord Ischemia

Compromise of a major segmental medullary artery can contribute to spinal cord ischemia. The neurological pattern depends on the vascular territory affected, the level of the cord involved, and the adequacy of collateral circulation.

Anterior spinal arterial insufficiency can affect motor pathways, anterior horn cells, and anterolateral sensory pathways. Posterior circulation compromise may preferentially involve structures such as the posterior columns, although actual infarction patterns can extend beyond simplified textbook vascular territories.

Segmental spinal arteries are therefore best understood as the regional gateways to the vascular supply of the vertebral canal and spinal cord. Their branches supply local vertebral and meningeal structures, follow spinal nerve roots, and, at selected levels, reinforce the anterior and posterior spinal arteries through segmental medullary vessels. Their variable distribution is a central feature of spinal vascular anatomy and explains why individual segmental arteries can have disproportionate importance for spinal cord perfusion.