Posterior Spinal Arteries

The posterior spinal arteries are paired longitudinal vessels that descend along the posterolateral aspect of the spinal cord. Together with the single anterior spinal artery, they form the principal longitudinal arterial system of the cord. The posterior spinal arteries supply predominantly the posterior portion of the spinal cord, including much of the posterior columns and adjacent peripheral white and gray matter.^[1][2]

Unlike the anterior spinal artery, which occupies the anterior median fissure as a relatively distinct midline vessel, each posterior spinal artery follows a less sharply defined longitudinal course near the attachment of the posterior spinal nerve roots. The arteries communicate extensively with surrounding pial vessels and may appear as an interconnected longitudinal arterial network rather than as two completely uniform vessels.

Blood flow through the posterior spinal arterial system is reinforced at variable levels by posterior segmental medullary arteries. These vessels reach the spinal cord through the intervertebral foramina and supplement the longitudinal circulation, making the posterior spinal arteries part of a broader segmental and pial vascular network.

Origin

The posterior spinal arteries arise intracranially near the medulla and upper cervical spinal cord. Their origin is variable. They commonly arise from the vertebral arteries or from the posterior inferior cerebellar arteries, which themselves are branches of the vertebral arteries.^[1][3]

A posterior spinal artery is present on each side. After arising near the craniovertebral junction, each vessel descends toward the posterior surface of the spinal cord and contributes to the longitudinal arterial network extending along the cord.

The variable origin of these arteries is an important feature of their anatomy. Regardless of the exact proximal source, their spinal circulation is subsequently supported by segmental arterial contributions along the vertebral column.

Course

The posterior spinal arteries descend along the posterolateral surface of the spinal cord, generally near the line of attachment of the posterior nerve roots.

Their course is less confined to a single deep groove than that of the anterior spinal artery. Instead, each posterior spinal artery is closely associated with a network of pial vessels distributed over the surface of the cord.

As the arteries descend, they receive variable reinforcement from posterior segmental medullary arteries. Numerous anastomotic connections also link the posterior vessels with each other and with branches of the anterior spinal arterial circulation.

Relationship to the Posterior Nerve Roots

The posterior spinal arteries lie close to the posterior root entry zone, where sensory nerve rootlets enter the posterolateral surface of the spinal cord.

Spinal branches of regional arteries enter the vertebral canal through the intervertebral foramina. Some of these branches accompany the posterior roots as posterior radicular arteries. Most radicular arteries primarily supply the nerve roots and associated tissues, but selected larger vessels continue to the spinal cord and reinforce the posterior spinal arteries.

These larger vessels are termed posterior segmental medullary arteries. The distinction between radicular and segmental medullary arteries is important because not every artery accompanying a spinal nerve root contributes directly to the longitudinal arterial supply of the spinal cord.

Segmental Reinforcement

The longitudinal posterior spinal arteries do not function independently of regional arterial sources. They are reinforced at multiple, variable levels by vessels derived from segmental arteries outside the vertebral canal.

Depending on the level of the vertebral column, spinal branches may arise from arterial territories including the vertebral, ascending cervical, deep cervical, posterior intercostal, lumbar, and lateral sacral arteries.^[1][2]

These spinal branches enter the vertebral canal through the intervertebral foramina. Some terminate in the vertebrae, meninges, or nerve roots, while selected branches reach the spinal cord and join the longitudinal arterial system.

Arterial Component	Principal Role
Posterior spinal arteries	Paired longitudinal supply to the posterior spinal cord
Posterior radicular arteries	Supply posterior spinal nerve roots
Posterior segmental medullary arteries	Reinforce the posterior spinal arteries
Anterior spinal artery	Supplies predominantly the anterior and central spinal cord
Pial arterial network	Connects arterial territories around the circumference of the cord

Posterior Segmental Medullary Arteries

The posterior segmental medullary arteries are larger spinal arterial branches that reach the posterior surface of the spinal cord and reinforce the posterior spinal arteries. They accompany posterior nerve roots toward the cord.

The number and levels of these vessels vary considerably. They are not present as major contributors at every spinal level. This discontinuous pattern of reinforcement is characteristic of the arterial supply of the spinal cord.

In contrast with the anterior circulation, where the great anterior segmental medullary artery may form a particularly dominant contribution to the lower cord, the posterior circulation is generally supported by a greater number of segmental connections distributed along the cord.

Pial Arterial Network

The surface of the spinal cord contains an extensive arterial plexus formed by branches of the anterior and posterior spinal arteries. This network is commonly called the vasocorona.

The vasocorona encircles the spinal cord and provides circumferential connections between the anterior and posterior longitudinal arterial systems. Small branches arising from this network penetrate the peripheral portions of the spinal cord.

The posterior spinal arteries therefore should not be viewed as isolated vessels supplying sharply separated territories. Their branches participate in an interconnected pial circulation with overlapping vascular distributions.

Branches

The posterior spinal arteries give rise to numerous small branches that spread over and penetrate the posterior spinal cord. Their distribution differs from the deeper central supply arising from the anterior spinal artery.

Branches from the posterior spinal arterial system supply the posterior columns and portions of the posterior horns. Peripheral branches also communicate with the vasocorona and contribute to the supply of superficial white matter around the circumference of the cord.

The arterial territories overlap at their margins, so the boundary between anterior and posterior spinal arterial supply is not an exact line.

Territory of Supply

The posterior spinal arteries supply predominantly the posterior one-third of the spinal cord. This conventional description is useful for understanding the major vascular territories but should not be interpreted as a precise geometric division.

Their territory includes much of the following:

• Posterior columns: Ascending pathways carrying information important for discriminative touch, vibration, and conscious proprioception.
• Posterior horns: Portions of the dorsal gray matter involved in processing sensory information.
• Posterolateral white matter: Peripheral regions supplied through posterior spinal and pial arterial branches.

Central portions of the cord receive substantial supply from sulcal branches of the anterior spinal artery, while peripheral territories receive additional contributions from the circumferential pial network.

Supply of the Posterior Columns

The posterior columns, also called the dorsal columns, occupy the posterior funiculi of the spinal cord. They contain the fasciculus gracilis throughout the cord and, above the upper thoracic region, the fasciculus cuneatus.

These ascending pathways transmit sensory information related principally to fine or discriminative touch, vibration, and conscious proprioception. Their predominant arterial supply from the posterior spinal arteries helps explain the sensory pattern that can occur when posterior spinal circulation is selectively impaired.

The posterior column territory contrasts with the major motor and anterolateral sensory pathways that lie largely within the territory supplied by the anterior spinal arterial system.

Relationship to the Anterior Spinal Artery

The posterior spinal arteries and anterior spinal artery form complementary components of the longitudinal spinal circulation.

Feature	Anterior Spinal Artery	Posterior Spinal Arteries
Number	One longitudinal artery	Paired longitudinal arteries
Position	Anterior median fissure	Posterolateral spinal cord near posterior root entry zones
Major territory	Approximately anterior two-thirds	Approximately posterior one-third
Important pathways	Corticospinal and anterolateral systems within its territory	Posterior column pathways within its territory
Segmental reinforcement	Anterior segmental medullary arteries	Posterior segmental medullary arteries

The two systems communicate through the vasocorona and other pial anastomoses. Their territories are therefore interconnected and overlap rather than being completely independent.

Regional Sources of Arterial Reinforcement

The arterial sources providing spinal branches change along the length of the vertebral column.

Region	Potential Sources of Spinal Branches
Cervical	Vertebral, ascending cervical, and deep cervical arteries
Thoracic	Posterior intercostal arteries
Lumbar	Lumbar arteries
Sacral	Lateral sacral and related pelvic arteries

Only selected spinal branches continue as segmental medullary arteries. Others terminate in the spinal nerve roots, meninges, vertebral structures, or surrounding tissues.

Relationship to the Meninges

The posterior spinal arteries lie within the subarachnoid space and are closely applied to the pia mater covering the spinal cord. Their branches participate in the vascular network associated with the pial surface.

The vessels are therefore internal to the dura mater and arachnoid mater. Cerebrospinal fluid within the subarachnoid space surrounds the cord, nerve roots, and associated vessels.

Small meningeal branches from regional spinal arteries also supply the coverings of the spinal cord, but these should be distinguished from the arteries that directly supply spinal cord tissue.

Anatomical Variation

The posterior spinal arterial system shows considerable anatomical variation. The proximal arteries may arise directly from the vertebral arteries or through the posterior inferior cerebellar arteries, and their caliber and continuity can differ between sides and between individuals.

Segmental reinforcement is also variable. The number, size, and vertebral levels of posterior segmental medullary arteries are not identical from one person to another.

The extensive pial network further means that the posterior circulation may not appear as two simple uninterrupted arteries throughout its entire length. Describing paired posterior spinal arteries remains anatomically useful, but the actual vascular pattern is more plexiform than the simplified textbook representation may suggest.

Clinical Significance

Ischemia confined predominantly to the posterior spinal arterial territory is less common than anterior spinal artery syndrome. When it occurs, the neurological findings reflect involvement of posterior spinal cord structures, particularly the posterior columns.

Posterior Spinal Artery Infarction

Infarction of the posterior spinal arterial territory can impair functions carried by the posterior columns. Depending on the level and extent of injury, this may produce loss or reduction of vibration sense, discriminative touch, and conscious proprioception below the affected level.

Loss of proprioceptive input can produce sensory ataxia because accurate information about limb and joint position is required for coordinated movement. The precise clinical pattern varies because spinal cord infarcts do not always conform perfectly to simplified arterial territory diagrams.^[3][4]

Comparison with Anterior Spinal Artery Syndrome

Anterior spinal artery syndrome typically affects motor pathways and the anterolateral sensory system while relatively sparing posterior column modalities. Posterior spinal arterial ischemia produces a different pattern because the posterior columns lie within its principal vascular territory.

This distinction illustrates the relationship between spinal cord vascular anatomy and neurological examination, although real vascular lesions may cross arterial boundaries or involve more than one vascular territory.

Spinal Procedures and Surgery

Operations involving the vertebral column, spinal canal, intervertebral foramina, or regional segmental vessels require awareness of the arterial supply of the cord. Posterior segmental medullary arteries may accompany nerve roots through the foramina and contribute directly to the posterior spinal circulation.

Their variable number and location mean that individual arterial anatomy cannot always be predicted from vertebral level alone. When vascular preservation is particularly important, preoperative or intraoperative imaging may be used to define relevant vessels.

The posterior spinal arteries are best understood as paired components of an interconnected longitudinal and pial arterial network. They descend near the posterior root entry zones, receive variable segmental reinforcement, communicate with the anterior spinal circulation through the vasocorona, and provide the predominant arterial supply to the posterior spinal cord and its posterior column pathways.