Veins of Spinal Cord, Nerve Roots, and Vertebrae

The external vertebral plexus consists of anterior and posterior parts, which anastomose freely. The veins forming the anterior external plexus lie in front of the vertebral bodies, from which they receive venous tributaries and through which they communicate with the basivertebral veins. The posterior external plexus is a network located over the vertebral laminae and extending around the spinous, transverse, and articular processes. In the upper cervical region, the posterior plexus communicates with the occipital veins and, via these, with the mastoid and occipital emissary veins. The posterior plexus also communicates with the vertebral and deep cervical veins, and a few channels pass through the foramen magnum to the dural sinuses in the posterior cranial fossa.

The internal vertebral plexus is formed by networks of veins lying in the epidural space within the vertebral canal. The networks are arranged in anterior and posterior groups, which are interconnected by many smaller oblique and transverse channels. The anterior internal plexus consists of longitudinal veins lying on the posterior surfaces of the vertebral bodies and intervertebral disks found on each side of the posterior longitudinal ligament. Interconnecting branches lie between the ligament and the vertebral bodies and receive the basivertebral veins. The longitudinal veins in the posterior internal plexus are smaller than their anterior counterparts. They are located on each side of the median plane in front of the vertebral arches and ligamenta flava. They anastomose with the veins of the posterior external vertebral plexus via small veins that pierce the ligaments and pass between them.

The basivertebral veins resemble the cranial diploë, and tunnel through the cancellous tissue of the vertebral bodies. They converge to form a comparatively large, single (occasionally, double) vein that emerges through the posterior surface of the vertebral body to end, via openings guarded by valves, in the transverse interconnections of the anterior internal vertebral plexus. The basivertebral veins also drain into the anterior external plexus through openings in the front and sides of the vertebral body.

The veins of the spinal cord resemble the related arteries in their distribution and form a tortuous plexus in the pia mater (see Plate 2-5). Intrinsic veins from the anteromedial region of the spinal cord and radial veins from the anterior funiculus drain into the anterior median spinal (longitudinal)vein, sometimes duplicated. Capillaries and venules from the rest of the spinal cord drain by radial veins into the coronal veins on the posterior and lateral surface of the spinal cord. These superficial veins drain, in turn, by the anterior and posterior medullary veins, sometimes called radicular veins, which accompany the nerve roots and radicular or radiculomedullary arteries. The medullary veins unite with radicular veins draining the nerve roots and with branches from the anterior and posterior internal vertebral plexuses to form the intervertebral veins. Above, the spinal veins communicate with veins draining the medulla oblongata and the inferior surface of the cerebellum through the foramen magnum.

The intervertebral veins drain most of the blood from the spinal cord and from the internal and external vertebral venous plexuses. They accompany the spinal nerves through the intervertebral foramina and end in the vertebral, posterior intercostal, subcostal, lumbar, and lateral sacral veins. Their orifices are usually protected by valves.

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