Vertebral venous plexus
The vertebral venous plexus is a highly anastomotic network of valveless veins running along the entire length of the vertebral column from the foramen magnum to the sacral hiatus.
The vertebral venous plexus is comprised of three interconnected divisions:
- internal vertebral venous plexus
- external vertebral venous plexus
- basivertebral veins
The internal vertebral venous plexuses and external vertebral venous plexuses communicate with one another via the intervertebral veins, which run through the intervertebral foramina.
Internal vertebral venous plexus
The internal vertebral venous plexuses consist of two anterior and two posterior interconnecting longitudinal vessels lying in the epidural space and surrounded by a small collection of semi-liquid fat. They receive tributaries from the radicular and basivertebral veins as well as the Batson plexus.
The anterior internal vertebral venous plexus is more prominent and largely lies posterior to the vertebral bodies, while the posterior internal vertebral venous plexus largely lies anterior to the laminae.
External vertebral venous plexus
The external vertebral venous plexuses are composed of the anterior and posterior external vertebral plexuses that surround the vertebral column. In addition to the internal vertebral venous plexus, they form several connections with the azygos, lumbar and deep cervical veins.
The anterior external vertebral venous plexus lies anterior to the vertebral bodies while the posterior external vertebral venous plexus lies posterior to the vertebral arch.
The basivertebral veins course horizontally within the vertebral bodies, receiving tributaries from numerous small venous channels. These are drained posteriorly by the anterior internal vertebral venous plexus and anteriorly by the external vertebral venous plexus.
As such, and owing to its unvalved nature, the vertebral venous plexus is subject to distension in cases of increased intrathoracic or intra-abdominal pressure due to ascites, pregnancy, large tumors, etc. This leads to an increased risk of trauma during needle placement into the epidural space.