Vertebral Venous Plexus
On this page
Direct answer
Batson's plexus — the valveless vertebral venous network — runs the length of the spinal column as an internal (epidural) plexus inside the vertebral canal between the dura and periosteum, and an external plexus on the vertebral bodies and arches, the two linked by basivertebral veins from the marrow of each body and by intervertebral veins leaving through each intervertebral foramen. The intervertebral veins drain into the segmental veins — vertebral, deep cervical, posterior intercostal, lumbar and lateral sacral — which empty into the azygos system and the inferior vena cava. Superiorly the plexus is continuous through the foramen magnum with the occipital and basilar sinuses, and hence with the whole intracranial dural sinus system including the cavernous sinus. Because no valve exists anywhere in the network, blood flows wherever pressure directs it — the property that lets prostate carcinoma reach the vertebrae and even the brain without passing through the lungs.
What you must remember
- Four plexuses in two planes: internal anterior and posterior (epidural, in the canal) and external anterior and posterior (on the vertebral bodies and on the laminae and spines); the internal anterior pair is the largest, lying on the posterior longitudinal ligament.
- Valvelessness as the organising fact: flow direction reverses with raised intrathoracic or intra-abdominal pressure — coughing, straining, Valsalva — propelling pelvic and abdominal blood into the plexus.
- Cranial continuity: through the foramen magnum the occipital and basilar plexuses join the cavernous and other dural sinuses, making the spine a venous extension of the skull's interior.
- Segmental exit: intervertebral veins accompany the spinal nerves through the intervertebral foramina to the vertebral, deep cervical, intercostal, lumbar and lateral sacral veins, ultimately to the azygos system and inferior vena cava.
- Metastasis highway: prostate, breast, lung, kidney and thyroid carcinomas seed the vertebral bodies — prostate classically producing osteoblastic (sclerotic) lumbar and pelvic metastases — and may even reach the brain bypassing the pulmonary capillary filter.
- Epidural anaesthesia relevance: the plexus fills the epidural space with fat and veins; intravascular injection of local anaesthetic is the feared complication, prevented by aspiration and a test dose — and the space distends (and bleeds more) in pregnancy and in the sitting, awake patient.
- Bleeding encounters: lumbar puncture and spinal surgery frequently meet the plexus — a "blood tap" or troublesome epidural venous ooze — and vertebral haemangiomas, the commonest benign vertebral tumours, arise from these channels.
Why the spine fills with prostate cancer
An elderly man presents with relentless lower back pain and sclerotic patches through the lumbar spine and pelvis on X-ray; his prostate-specific antigen is high. The anatomy explains why bone, and why there. The prostatic venous plexus communicates freely with the internal vertebral plexus through the lateral sacral and ascending lumbar veins; during straining, blood with its tumour emboli is pushed up this valveless ladder into the vertebral bodies, whose red marrow traps the cells. This is Batson's 1940 demonstration: it resolves why vertebrae are a first metastatic site when the arterial route would demand lung deposits first, and why prostate carcinoma reaches the brain without visible lung disease. The same reverse flow explains how pelvic sepsis seeds the epidural space and why a cough can pump venous blood up the entire column.
High-yield viva angles
Examiners frame three questions here. "Why is the epidural space vascular, and what does that mean for the anaesthetist?" — it contains fat, lymphatics and this plexus; accidental intravascular injection causes perioral tingling, tinnitus or frank local-anaesthetic toxicity and seizures, so aspirate before injecting and use a test dose. "Why does an epidural blood patch work?" — injecting the patient's own blood into the epidural space seals the dural hole and tamponades the plexus, relieving the post-dural puncture headache. And "why do metastases respect the venous geography?" — the lower thoracic and lumbar bodies, drained by the largest basivertebral channels, top the distribution lists.
Frequently asked questions
What are the divisions of the vertebral venous plexus?
An internal (epidural) plexus inside the vertebral canal with anterior and posterior parts, and an external plexus on the vertebral bodies and posterior elements, all interconnected and valveless.
How does the vertebral plexus connect with the intracranial venous sinuses?
Through the foramen magnum, where it is continuous with the occipital and basilar plexuses, and thereby with the cavernous sinus and the rest of the dural venous sinus system.
Why can prostate carcinoma metastasise to vertebrae without lung deposits?
Tumour emboli pass from the prostatic plexus into the valveless Batson's plexus during straining, reaching vertebral marrow directly and bypassing the pulmonary capillary bed.
What precaution does the vertebral venous plexus impose during epidural anaesthesia?
Aspirate before injecting and use a test dose, because the rich plexus risks intravascular injection with systemic toxicity.
What is a blood tap in lumbar puncture, and why does it occur?
Aspiration of blood because the needle has entered the epidural venous plexus — a reminder that the space between ligamentum flavum and dura is a venous sheet, not empty.