External vertebral venous plexuses
The external venous network, known as the external vertebral venous plexuses (plexus venosi vertebrales externi), is located directly on the outer surface of the bony structures of the vertebral column. Depending on the topography relative to the vertebrae, this vascular network is divided into two separate, yet interconnected parts:
- Anterior external vertebral venous plexus (plexus venosus vertebralis externus anterior). This structure encompasses the anterior parts of the spine. Its main function is to collect venous blood from the anterior elements of the axial skeleton. Specifically, this plexus receives blood from the vertebral bodies themselves, the adjacent anterior longitudinal ligament, and neighboring muscle groups, such as the deep cervical muscles.
- Posterior external vertebral venous plexus (plexus venosus vertebralis externus posterior). Located on the opposite, dorsal side. The vessels of this plexus densely encircle the posterior surface of the vertebral arches, as well as their transverse and spinous processes. Blood inflow into this part of the venous bed is derived from the deep back muscles, the skin of the back, and the posterior bony elements of the vertebrae themselves.
Internal vertebral venous plexuses
Unlike the superficial veins, the internal vertebral venous plexuses (plexus venosi vertebrales interni) are hidden inside the vertebral canal (canalis vertebralis). They have a significant length, accompanying the central nervous system along its entire course: these plexuses begin at the level of the foramen magnum of the cranium and descend downwards to the lower end of the sacral canal.
From the standpoint of topography within the canal, the internal plexuses run along the inner surface of its bony walls. They are located strictly in the epidural space, meaning they lie external to the dura mater protecting the spinal cord.
The internal system is also not uniform. Classification identifies two main venous pathways, which are abundantly interconnected by large blood vessels:
- Anterior internal vertebral venous plexus (plexus venosus vertebralis internus anterior).
- Posterior internal vertebral venous plexus (plexus venosus vertebralis internus posterior).
Basivertebral veins
A special element of the spinal drainage system is represented by the basivertebral veins (vv. basivertebrales). These are specialized intraosseous blood vessels that ensure the outflow of blood directly from the bulk of the bone tissue.
Basivertebral veins are formed and run in special channels located directly inside the spongy substance of the vertebral bodies. The course of these vessels is directed from the central parts of the bone to its posterior surface (i.e., towards the vertebral canal). Emerging from the vertebral body, the basivertebral veins empty into the anterior internal vertebral venous plexus, transferring the collected venous blood there.
Anastomoses and formation of venous rings
The venous system of the spine functions as a single entity due to an exceptionally well-developed network of anastomoses (connections between vessels). This ensures a reliable and uninterrupted outflow of blood.
Within the vertebral canal, the anterior and posterior internal plexuses regularly exchange blood. At the level of each vertebra, they connect with each other via transverse anastomoses. As a result of this connection, closed vascular structures—venous rings—are formed around the spinal cord.
In addition, there is a direct connection between the internal and external venous beds. This communication obeys strict anatomical logic:
- The posterior internal plexus communicates via vessels with the posterior external plexus.
- The anterior internal plexus sends anastomoses to the anterior external plexus.
Thus, blood can freely redistribute between the vertebral canal cavity and the external tissues of the spine.
Briefly: answers to topical questions
From which structures does the anterior external vertebral venous plexus collect blood?
The anterior external vertebral venous plexus (plexus venosus vertebralis externus anterior) collects venous blood from structures located on the anterior surface of the spinal column. The main sources of inflow include:
- Vertebral bodies — anterior parts of the bony structures.
- Anterior longitudinal ligament — the connective tissue structure of the spine.
- Deep cervical muscles — the adjacent muscular apparatus.
Through which openings do the anastomoses connecting the internal and external vertebral plexuses pass?
The anastomoses connecting the internal and external vertebral venous plexuses pass through the intervertebral foramina. The internal plexuses, located in the epidural space of the vertebral canal, form venous rings and communicate with the external plexuses (anterior and posterior) via these foramina. Outflow from the spinal cord also occurs via the intervertebral veins passing through these openings.
Into which veins does the systemic blood outflow from the vertebral venous plexuses occur?
The systemic outflow of blood from the vertebral venous plexuses occurs into the veins corresponding to the regions of the spinal column. Blood flows into the following vessels:
- Vertebral veins (vv. vertebrales) — collect blood in the cervical region (including the accessory vertebral vein).
- Posterior intercostal veins (vv. intercostales posteriores) — provide outflow in the thoracic region.
- Lumbar veins (vv. lumbales) — receive blood in the lumbar region.
- Lateral sacral veins (vv. sacrales laterales) — participate in outflow at the pelvic level.
The connection is carried out via the intervertebral veins (vv. intervertebrales).
With which dural venous sinuses do the internal vertebral plexuses communicate at the level of the foramen magnum?
At the level of the foramen magnum, the internal vertebral venous plexuses connect with the occipital sinus and the basilar plexus.
The topographic connection of the plexuses works like a direct mirror: the ANTERIOR internal communicates only with the ANTERIOR external, and the POSTERIOR internal strictly with the POSTERIOR external.
Class and exam questions
Where exactly are the internal vertebral venous plexuses located?
They are located directly inside the vertebral canal. Their exact localization is the epidural space, meaning they lie along the inner bony walls of the canal, external to the dura mater of the spinal cord.
Where do the basivertebral veins collect blood from and where do they carry it?
The basivertebral veins collect venous blood from the spongy substance of the vertebral bodies. They travel inside the bone toward the posterior surface of the vertebral body and empty into the anterior internal vertebral plexus.
How are the venous rings of the spine formed?
Venous rings are formed at the level of each individual vertebra. They are formed due to transverse anastomoses that connect the anterior and posterior internal vertebral venous plexuses with each other.
What structures are associated with the anterior external plexus?
The anterior external plexus is located on the anterior surface of the spine and collects blood from the vertebral bodies, the anterior longitudinal ligament, and adjacent muscles, such as the deep cervical muscles.
What else to study on this topic
- Detailed anatomy of the channels of the spongy substance for the basivertebral veins.
- Features of the topography of the anterior external plexus in the region of the deep cervical muscles.
- The nature of transverse anastomoses forming venous rings.
- Specifics of venous drainage from the dura mater of the spinal cord.
- Pathways of venous outflow from the deep muscles and skin of the back into the posterior external plexus.
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