Anterior Spinal Artery

The anterior spinal artery is the principal longitudinal artery supplying the anterior portion of the spinal cord. It begins superiorly from branches of the right and left vertebral arteries and descends along the anterior median fissure of the spinal cord. Through its penetrating and circumferential branches, it supplies much of the central and anterior spinal cord, conventionally described as approximately the anterior two-thirds of the cord.^[1][2]

The artery is not supplied along its entire length solely by blood entering from the vertebral arteries. As it descends, its circulation is reinforced at variable levels by anterior segmental medullary arteries arising indirectly from regional segmental vessels. This reinforcement is particularly important in the thoracic and lumbosacral regions, where the longitudinal spinal arteries alone are insufficient to maintain the entire blood supply of the cord.^[1]

The anterior spinal artery is clinically important because interruption of its blood supply can damage major motor and sensory pathways within the spinal cord. Its anatomy is also essential during procedures involving the vertebral column, thoracic and abdominal aorta, and vessels that contribute to the segmental arterial supply of the spinal cord.

Origin

Near the craniovertebral junction, each vertebral artery gives rise to a small anterior spinal branch. The paired branches descend and unite to form the anterior spinal artery.

The exact pattern of union can vary, and the vessel is better understood as part of a longitudinal arterial system than as a perfectly uniform single tube. After its formation, the anterior spinal artery continues inferiorly along the ventral surface of the spinal cord.^[1][3]

Its superior origin distinguishes it from the segmental arteries that subsequently reinforce it. The vertebral arteries establish the cranial portion of the longitudinal circulation, while additional arterial inflow reaches the system at selected levels along the vertebral column.

Course

The anterior spinal artery descends in the anterior median fissure of the spinal cord. This deep longitudinal groove separates the right and left anterior funiculi at the ventral surface of the cord.

The artery extends along the spinal cord toward the conus medullaris. During its descent, it receives blood from anterior segmental medullary arteries that enter the vertebral canal with spinal nerve roots and establish anastomoses with the longitudinal vessel.

The caliber of the anterior spinal artery and the pattern of its reinforcement are not uniform throughout the spinal cord. Segmental contributions vary considerably between individuals, making the arterial supply of the cord anatomically variable.

Segmental Reinforcement

The spinal cord receives additional arterial inflow from vessels derived from arteries outside the vertebral canal. These segmental vessels give rise to spinal branches that enter the intervertebral foramina.

Depending on the vertebral level, the parent vessels include branches associated with the vertebral, deep cervical, ascending cervical, posterior intercostal, lumbar, and lateral sacral arterial territories.^[1][2]

After entering an intervertebral foramen, a spinal branch may divide into branches associated with the vertebrae, meninges, and spinal nerve roots. Some radicular arteries supply the roots themselves, while a smaller number of larger vessels reach and reinforce the longitudinal spinal arteries. These are the segmental medullary arteries.

This distinction is important. Not every radicular artery supplying a spinal nerve root continues to the spinal cord, and not every vertebral level contributes an anterior segmental medullary artery.

Anterior Segmental Medullary Arteries

Anterior segmental medullary arteries accompany anterior roots toward the spinal cord and join the anterior spinal arterial system. Their number, size, and vertebral levels are variable.

These arteries provide essential reinforcement because blood flow through the longitudinal anterior spinal artery alone does not provide a uniform independent supply along the entire cord. Some regions therefore depend heavily on particular segmental inputs.

Arterial Component	Role
Anterior spinal artery	Longitudinal artery supplying much of the anterior and central spinal cord
Radicular arteries	Supply anterior or posterior spinal nerve roots
Anterior segmental medullary arteries	Reach and reinforce the anterior spinal artery
Posterior segmental medullary arteries	Reinforce the posterior spinal arterial system
Pial arterial network	Provides circumferential arterial connections around the spinal cord

Great Anterior Segmental Medullary Artery

The largest and most clinically important anterior segmental medullary artery is the great anterior segmental medullary artery, commonly called the artery of Adamkiewicz. It provides a major contribution to the arterial supply of the lower thoracic and lumbosacral spinal cord.

The artery usually arises from a posterior intercostal or lumbar arterial branch and most often enters the vertebral canal on the left side. Its level of origin is variable, although it most commonly arises in the lower thoracic to upper lumbar region.^[1][2]

After entering through an intervertebral foramen, it follows a spinal nerve root toward the cord and joins the anterior spinal artery. Its relatively large caliber makes it an important source of blood for the inferior portion of the anterior spinal arterial circulation.

Because its origin varies substantially, its location cannot be assumed from a single vertebral level in an individual patient.

Branches

The anterior spinal artery supplies the cord through two broad arterial patterns: penetrating central branches and circumferential branches associated with the pial arterial network.

Sulcal Arteries

Numerous sulcal arteries arise from the anterior spinal artery and enter the spinal cord through the anterior median fissure. These penetrating vessels supply much of the central gray matter and adjacent white matter.

Sulcal arteries commonly pass alternately toward the right and left sides rather than dividing symmetrically to supply both halves of the cord. Their distribution contributes substantially to the deep arterial supply of the spinal cord.^[1]

Pial Arterial Network

Branches of the anterior and posterior spinal arterial systems communicate around the surface of the cord through a pial arterial network, often referred to as the vasocorona.

This circumferential network contributes particularly to the peripheral portions of the spinal cord and creates connections between the anterior and posterior longitudinal arterial systems.

Territory of Supply

The anterior spinal artery and its branches conventionally supply approximately the anterior two-thirds of the spinal cord. This description is useful for understanding the major vascular territories, although the actual boundary is not a simple geometric division.

Structures substantially dependent on the anterior spinal arterial circulation include:

• Anterior horns: Contain lower motor neurons supplying skeletal muscle.
• Central gray matter: Much of the gray matter surrounding the central canal receives penetrating arterial supply from anterior spinal branches.
• Anterior funiculi: Contain several ascending and descending pathways.
• Lateral funiculi: Include major pathways such as the lateral corticospinal and anterolateral systems.
• Anterior commissural region: Includes crossing fibers of important sensory pathways.

The posterior columns are supplied predominantly by the posterior spinal arterial system and associated pial vessels, although arterial territories overlap at their margins.

Relationship to the Anterior Median Fissure

The anterior median fissure is a deep longitudinal groove on the ventral surface of the spinal cord. The anterior spinal artery follows this fissure throughout much of its course.

The vessel itself lies superficially in relation to the fissure, while sulcal branches enter the fissure and penetrate deeply into the cord. These branches then distribute blood to central and anterior spinal cord structures.

This relationship explains how a superficially positioned longitudinal artery supplies deep gray and white matter.

Relationship to the Spinal Nerve Roots

The segmental reinforcement of the anterior spinal artery is closely related to the spinal nerve roots. Spinal branches of regional arteries enter the vertebral canal through the intervertebral foramina alongside the spinal nerves.

Radicular branches accompany the anterior and posterior roots. Most primarily supply the roots and associated structures, while selected larger branches continue to the surface of the spinal cord as segmental medullary arteries.

Anterior segmental medullary arteries follow the anterior roots toward the cord before joining the anterior spinal arterial system. Their association with the roots provides the pathway by which arterial blood from outside the vertebral canal reaches the longitudinal vessels of the spinal cord.

Regional Sources of Spinal Arterial Supply

The parent arteries providing spinal branches differ according to vertebral level.

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

Only some of the spinal branches arising from these sources become segmental medullary arteries. This discontinuous pattern of reinforcement is a fundamental feature of spinal cord vascular anatomy.

Relationship to the Posterior Spinal Arteries

The anterior spinal artery is accompanied by paired posterior spinal arteries that descend along the posterolateral surface of the spinal cord. Together, these vessels form the principal longitudinal arterial system of the cord.

The posterior spinal arteries supply predominantly the posterior portion of the cord, particularly the posterior columns and adjacent structures. They also receive segmental reinforcement and communicate with the anterior circulation through the pial arterial network.

The anterior and posterior territories are therefore interconnected rather than completely isolated vascular compartments.

Anatomical Variation

Variation is a major feature of spinal cord arterial anatomy. The number and levels of segmental medullary arteries differ between individuals, and the relative importance of individual vessels varies along the length of the cord.

The artery of Adamkiewicz is especially variable in its vertebral level and side of origin. Although a left-sided origin is more common, right-sided origins occur. Other anterior segmental medullary arteries may also differ substantially in caliber.

The anterior spinal artery itself may show variations in caliber and continuity. Anastomoses within the pial arterial network provide additional connections, but they do not make every region equally resistant to interruption of major arterial inputs.

Clinical Significance

The clinical importance of the anterior spinal artery follows directly from the neural structures within its vascular territory. Interruption of the anterior spinal circulation can produce ischemia affecting motor pathways, anterior horn cells, and pathways carrying pain and temperature information.

Anterior Spinal Artery Syndrome

Anterior spinal artery syndrome refers to the neurological pattern produced by ischemia or infarction involving the anterior spinal arterial territory. The exact findings depend on the level and extent of the lesion.

Damage to the corticospinal tracts can produce motor deficits below the lesion. Involvement of anterior horn cells at the affected level may produce lower motor neuron findings in muscles supplied by those segments. Damage to the anterolateral system can impair pain and temperature sensation.

The posterior columns may be relatively preserved because their arterial supply is predominantly derived from the posterior spinal arterial system. As a result, modalities carried mainly in the posterior columns, including vibration and conscious proprioception, may be less affected than motor function and pain and temperature sensation.^[3][4]

Aortic Surgery

The segmental medullary arteries are particularly important during procedures involving the thoracic or abdominal aorta. Posterior intercostal and lumbar arteries arising from the aorta can provide critical segmental contributions to the anterior spinal circulation.

Interruption of important segmental vessels can reduce spinal cord perfusion. The artery of Adamkiewicz is of particular concern because of its major contribution to the lower spinal cord.

Spinal and Vertebral Procedures

Procedures involving the vertebral column, intervertebral foramina, or paravertebral region require awareness of the segmental arterial pathways supplying the spinal cord. Medullary vessels can accompany nerve roots through the foramina and may not be predictable from external anatomy alone.

When precise vascular localization is necessary, imaging can be used to identify major segmental contributors and their relationship to the vertebral column.

Spinal Cord Ischemia

The spinal cord depends on both its longitudinal arteries and segmental reinforcement. Reduced perfusion can therefore result from disease or injury affecting the anterior spinal artery itself, its parent vessels, or important segmental contributors.

The anterior spinal artery is best understood as the central longitudinal component of a larger arterial network. It begins from the vertebral arterial circulation, descends along the anterior median fissure, receives variable segmental reinforcement, and supplies much of the anterior and central spinal cord. This network arrangement explains both the complexity of spinal cord vascular anatomy and the neurological consequences that can follow interruption of critical arterial inputs.