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Posterior spinal veins

Medically Reviewed by Anatomy Team

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The posterior spinal veins are a network of veins that run along the posterior aspect of the spinal cord. They are located within the subarachnoid space in the spinal canal, specifically along the dorsal (back) surface of the spinal cord. These veins run parallel to the spinal cord, extending from the cervical region down to the sacral region. The posterior spinal veins are part of a larger venous system that includes the anterior spinal veins, which together form a venous plexus around the spinal cord. They drain into the internal vertebral venous plexus, which is situated within the vertebral column.

Location

The posterior spinal veins are situated along the dorsal (posterior) aspect of the spinal cord, running longitudinally from the cervical region at the base of the skull down to the sacral region at the lower end of the vertebral column. They are located within the subarachnoid space of the spinal canal, surrounded by cerebrospinal fluid (CSF), and positioned posterior to the spinal cord. These veins form part of the venous plexus system that encircles the spinal cord and are contained within the layers of the spinal meninges, specifically between the arachnoid mater and pia mater.

Anatomy

Structure

The posterior spinal veins are not single continuous vessels but consist of a longitudinal network of interconnected veins that run parallel to the spinal cord. Typically, there are two main posterior spinal veins, one on each side of the midline, running along the dorsal surface of the spinal cord. These veins are interconnected by smaller transverse and oblique venous branches, forming a rich network of anastomoses that provide redundancy and multiple pathways for venous drainage. The posterior spinal veins form part of the spinal venous plexus, which includes both the anterior and posterior spinal veins.

Relations

  • Anterior relations: The posterior spinal veins are situated directly posterior to the spinal cord, separated from the anterior spinal veins by the spinal cord itself. They are enclosed within the subarachnoid space, lying deep to the arachnoid mater and in direct contact with the pia mater.
  • Posterior relations: The veins are related posteriorly to the arachnoid mater and the dura mater, the outermost meningeal layers. Further posteriorly, the veins are adjacent to the vertebral laminae and the ligamentum flavum that form the posterior boundary of the vertebral canal.
  • Lateral relations: The lateral extensions of the posterior spinal veins connect with smaller venous channels that run along the sides of the spinal cord, ultimately merging with the internal vertebral venous plexus within the epidural space.

Venous Network and Anastomoses

The posterior spinal veins are part of a complex spinal venous plexus that includes the anterior spinal veins and smaller segmental veins.[1] These veins are interconnected through a series of transverse and oblique anastomosing branches that allow blood to flow between the posterior and anterior venous systems. This network of veins is supported by smaller radicular veins, which enter the spinal canal at various vertebral levels. The venous network is highly interconnected, allowing for variations in venous flow based on positional changes and pressure gradients.

Tributaries

The posterior spinal veins receive venous blood from several tributaries that drain different components of the spinal cord and its associated structures:

  • Radicular veins: These veins accompany the spinal nerve roots and drain into the posterior spinal veins. Radicular veins enter the spinal canal at each vertebral level and provide a pathway for venous blood from the spinal cord and nerve roots to reach the larger venous plexus.
  • Medullary veins: These veins drain the central gray matter of the spinal cord and contribute to the venous return through both the anterior and posterior spinal veins.[2]
  • Dorsal sulcal veins: Small veins that drain the dorsal surface of the spinal cord and empty directly into the posterior spinal veins.

Course

The posterior spinal veins run longitudinally along the entire length of the spinal cord, starting in the cervical region at the upper part of the spinal canal and continuing down to the thoracic, lumbar, and sacral regions.[3] They maintain a parallel course along the dorsal surface of the spinal cord and are enclosed within the layers of the meninges. Throughout their course, these veins are joined by smaller segmental veins and radicular veins that enter the spinal canal through the intervertebral foramina at each vertebral level.

Termination

The posterior spinal veins terminate by draining into the internal vertebral venous plexus, which is located within the epidural space of the spinal canal. The internal vertebral venous plexus is a complex network of veins that runs along the length of the vertebral column and communicates with the external venous plexus outside the vertebrae. From the internal vertebral venous plexus, venous blood is further drained into larger systemic veins, such as the vertebral veins, azygos veins, and segmental veins, depending on the spinal level.

Communication with the Anterior Spinal Veins

The posterior spinal veins are connected to the anterior spinal veins through a series of small transverse anastomosing veins that run across the surface of the spinal cord. These connections form a venous ring around the spinal cord at each segmental level, allowing for efficient venous drainage from both the anterior and posterior surfaces. This network of anastomoses provides flexibility in venous flow and helps balance venous pressure across different regions of the spinal cord.[4]

Variations

The anatomy of the posterior spinal veins can show anatomical variations in size, number, and pattern of anastomoses. In some individuals, the posterior spinal veins may be larger or more prominent, while in others, they may form multiple smaller channels that merge at various levels. The number and arrangement of the transverse anastomotic veins connecting the posterior and anterior systems can also vary, leading to different patterns of venous drainage across the spinal cord.

Function

Venous Drainage of the Posterior Spinal Cord

The primary function of the posterior spinal veins is to drain deoxygenated blood from the posterior aspect of the spinal cord. These veins collect blood from the dorsal part of the spinal cord, including the spinal cord tissue, meninges, and associated structures.[6] The posterior spinal veins play a vital role in ensuring that blood is efficiently drained from these tissues, allowing for proper circulation and metabolic waste removal. This drainage helps prevent blood from pooling in the spinal cord, ensuring that the spinal cord tissue remains healthy and functional.

Drainage of Venous Blood from the Dorsal Gray and White Matter

The posterior spinal veins are involved in draining venous blood from the dorsal gray matter and white matter of the spinal cord. The gray matter contains nerve cell bodies and synapses involved in sensory and motor processing, while the white matter contains the myelinated axons responsible for transmitting nerve signals. The posterior spinal veins collect venous blood from these regions, ensuring the removal of deoxygenated blood and metabolic waste products that accumulate during neural activity. This drainage is critical for maintaining the health and function of the neurons and glial cells in the spinal cord.

Removal of Metabolic Waste from Spinal Cord Tissue

As part of their venous drainage function, the posterior spinal veins help remove metabolic waste from the spinal cord tissue. During normal cellular processes, especially neural activity, the cells of the spinal cord produce metabolic byproducts, including carbon dioxide and other waste products. The posterior spinal veins ensure that these waste materials are removed from the spinal cord and transported to the larger venous system for processing and elimination. This process is essential for maintaining the metabolic balance of the spinal cord tissue and preventing the buildup of toxic byproducts.

Communication with the Anterior Spinal Veins

The posterior spinal veins are connected to the anterior spinal veins via transverse anastomoses. This communication allows for the redistribution of venous blood between the anterior and posterior venous systems of the spinal cord. If there is increased pressure in one part of the venous system, blood can be redirected to the other system, ensuring balanced venous drainage. This communication helps regulate venous pressure within the spinal cord, preventing congestion in any specific area and promoting efficient venous return.

Venous Return from Spinal Nerve Roots

The posterior spinal veins are responsible for draining venous blood from the spinal nerve roots, particularly the dorsal (sensory) nerve roots. Each segment of the spinal cord has nerve roots that extend outward through the intervertebral foramina to form the spinal nerves. The posterior spinal veins collect blood from these nerve roots, ensuring that the nerves and associated tissues are adequately drained. This function is crucial for maintaining the health of the sensory nerve roots and preventing issues such as venous congestion, which could impair nerve function.

Connection to the Internal Vertebral Venous Plexus

The posterior spinal veins are part of a larger venous network that connects to the internal vertebral venous plexus. This plexus is located in the epidural space surrounding the spinal cord and vertebrae. By draining into the internal vertebral venous plexus, the posterior spinal veins ensure that venous blood from the spinal cord is efficiently transported to the larger systemic venous circulation. This connection to the vertebral venous system is important because it provides a pathway for blood to travel from the spinal cord to major veins like the vertebral veins, azygos vein, and segmental veins.

Support for Venous Return During Movement

During movement, such as bending, twisting, or extending the spine, the posterior spinal veins assist in maintaining venous return from the spinal cord. The dynamic nature of the spine and surrounding muscles can create fluctuations in pressure within the spinal canal. The posterior spinal veins, with their network of anastomoses and tributaries, help accommodate these pressure changes, ensuring continuous venous return despite the movement of the vertebral column. This adaptability ensures that blood flow is not interrupted during physical activities.

Regulation of Venous Pressure in the Spinal Cord

The posterior spinal veins play a key role in regulating venous pressure within the spinal cord. They help balance the flow of blood between the anterior and posterior spinal veins, as well as between the venous systems of different spinal segments.[7] If venous pressure increases in one area due to increased blood flow or positional changes, the posterior spinal veins help redistribute the blood to lower-pressure areas through their anastomotic connections. This regulation of pressure is critical for maintaining the integrity of the spinal cord and ensuring smooth venous return.

Drainage from the Meninges and Surrounding Structures

The posterior spinal veins also contribute to the drainage of blood from the meninges—the protective layers that cover the spinal cord, including the dura mater, arachnoid mater, and pia mater. As part of their drainage role, these veins help remove blood from the vascularized meninges, especially from the pia mater, which is closely associated with the surface of the spinal cord. This function is essential for preventing the buildup of venous blood in the meninges and ensuring that the protective coverings of the spinal cord remain healthy.

Venous Drainage from the Posterior Sulcal Region

In addition to draining the broader posterior surface of the spinal cord, the posterior spinal veins are responsible for draining venous blood from the posterior sulcal region—the grooves and fissures on the dorsal surface of the spinal cord. The veins located in these sulci, known as dorsal sulcal veins, feed into the larger posterior spinal veins, ensuring that even the deeper parts of the posterior spinal cord are adequately drained.

Clinical Significance

The posterior spinal veins are clinically significant due to their role in spinal cord drainage and their involvement in various neurological and vascular conditions. Obstruction or compression of these veins, such as in conditions like spinal cord tumors, epidural hematomas, or spinal arteriovenous malformations, can lead to impaired venous drainage, resulting in venous congestion and increased pressure within the spinal cord.[8] This can cause symptoms such as back pain, motor weakness, or even neurological deficits if blood flow is significantly disrupted.

The posterior spinal veins are also involved in certain pathological conditions like spinal cord edema or myelopathy, where impaired venous return can exacerbate spinal cord damage. During surgical procedures involving the spine, such as decompression surgeries or spinal tumor resections, care must be taken to avoid damaging these veins, as injury can lead to complications like bleeding or venous thrombosis, which can further compromise spinal cord function.

References

  1. Clemente, C. D. (2012). Clemente’s Anatomy Dissector (5th ed.). Lippincott Williams & Wilkins.
  2. Haines, D. E. (2013). Fundamentals of Human Neuroanatomy. McGraw-Hill Education.
  3. Tandler, J., & Hennemann, H. (2007). Anatomy of the Human Vertebral Column and Spinal Cord. Springer.
  4. Rhoton, A. L. (2002). The Neurosurgical Atlas. Quality Medical Publishing.
  5. Gross, J. (2000). The Human Nervous System (2nd ed.). Academic Press.
  6. Naidich, T. P., & Lee, K. S. (2011). Imaging of the Spine (2nd ed.). Wolters Kluwer.
  7. Yasargil, M. G. (2011). Microsurgery of the Spine. Thieme Medical Publishers.
  8. Williams, P. L., Bannister, L. H., Berry, M. M., & Collins, P. (1995). Gray’s Anatomy: The Anatomical Basis of Clinical Practice (38th ed.). Churchill Livingstone.