What is the blood supply and venous drainage of the thoracic and lumbar spine, and how does it relate to the spread of infection and secondary metastasis in adults?

Blood Supply and Venous Drainage of the Thoracolumbar Spine

Arterial Blood Supply

The thoracolumbar spinal cord receives its arterial supply through a continuous anterior spinal artery system fed by segmental vessels, with the critical arteria radicularis magna (artery of Adamkiewicz) most commonly arising from lumbar arteries rather than thoracic vessels. 1

Primary Arterial Architecture

• The anterior spinal artery forms an uninterrupted pathway extending from the vertebral arteries superiorly through connections with posterior intercostal and lumbar arteries throughout the thoracolumbar region 1
• Posterior intercostal arteries arise as 7 pairs in 80% of cases, 8 pairs in 15%, and 9 pairs in 5% from the thoracic aorta 2
• Five pairs of lumbar arteries consistently arise from the abdominal aorta in all individuals 2
• The arterial supply includes both central and peripheral components through the vasocorona network, with the anterior spinal artery supplying central structures and posterior spinal arteries supplying peripheral components 3

Critical Vascular Landmarks

• The arteria radicularis magna (artery of Adamkiewicz) arises from a lumbar artery in 70.5% of cases and is left-sided in 62.7% 1
• This vessel exhibits significant anatomical variability, with its origin ranging from T9 to L5 1
• Branches entering the ventral spinal artery are left-sided in 64.2% and right-sided in 35.8% of cases throughout the thoracolumbar region 2
• Branches supplying the dorsal spinal arteries are left-sided in 60.8% and right-sided in 39.2% 2

Vertebral Body Perfusion

• Vertebral bodies receive blood through 2 posterior central arteries originating from ascending branches on the dorsal plane 4
• 2-3 anterior central arteries supply the ventrolateral plane, with all vessels converging centrally within the vertebral body 4
• Large arched anastomoses exist between ascending and descending branches on the dorsal vertebral body surface 4
• Intervertebral discs receive lateral vascular supply through dedicated rami disci intervertebralis 4

Venous Drainage System

Venous Architecture and Asymmetry

• Lumbar veins rarely demonstrate bilateral pairing, contrasting sharply with the more consistent pairing of lumbar arteries 5
• These veins preferentially drain into the left side of the inferior vena cava and diverge closer to the iliocaval confluence 5
• The perimedullary venous system includes longitudinal anastomotic chains interconnected by the coronary plexus 3
• Radiculomedullary veins follow spinal nerve roots to the epidural plexus, with their passage through the thecal sac forming a valve-like antireflux mechanism 3

Venous Pressure Dynamics

• When CSF pressure exceeds spinal venous pressure, a "critical closing pressure" occurs where veins collapse independent of inflow pressure, critically affecting spinal cord perfusion 6, 7, 8
• This phenomenon has direct implications for understanding how venous congestion can compromise spinal cord blood flow 6

Clinical Relevance to Infection Spread

Mechanisms of Infectious Dissemination

The extensive anastomotic network and valveless nature of spinal veins create bidirectional flow patterns that facilitate hematogenous spread of infection to vertebral bodies and epidural spaces.

• Infection can spread to the spine through three primary mechanisms: contiguous spread from adjacent structures (mediastinitis, paravertebral abscess), septic emboli from bacterial endocarditis, and hematogenous dissemination during sepsis or IV drug abuse 6
• The rich vascular plexus surrounding vertebral bodies provides multiple entry points for bloodborne pathogens 4
• Staphylococcus aureus and Salmonella are the most commonly identified organisms in spinal infections 6
• Infection typically arises in diseased tissue, including preexisting aneurysms, atherosclerotic plaques, or sites of prior trauma 6

Anatomical Vulnerabilities

• The central convergence of 4-5 arteries within each vertebral body creates a vascular watershed area susceptible to seeding during bacteremia 4
• Anastomotic connections between ascending and descending branches provide continuous pathways for infection spread across multiple spinal levels 4
• The epidural venous plexus, with its valve-like antireflux mechanisms at radiculomedullary vein entry points, can paradoxically trap infected emboli 3

Clinical Relevance to Metastatic Spread

Batson's Venous Plexus Concept

The valveless vertebral venous system allows bidirectional flow that bypasses portal and caval systems, explaining the predilection of certain cancers to metastasize to the spine despite relatively low cardiac output to vertebral structures.

• The preferential left-sided drainage pattern and asymmetric venous anatomy create predictable patterns of metastatic seeding 5
• Increased intra-abdominal or intrathoracic pressure can reverse flow direction in the valveless vertebral venous plexus, propelling tumor cells from pelvic, prostatic, breast, or lung primaries directly to vertebral bodies
• The rich anastomotic network between segmental veins allows tumor emboli to spread across multiple spinal levels once they enter the vertebral venous system 3

Arterial Metastatic Pathways

• The continuous anterior spinal artery system provides an uninterrupted pathway for arterial tumor emboli throughout the entire spinal axis 1
• The variability in arteria radicularis magna origin (T9-L5) means that arterial emboli can access different spinal levels depending on individual vascular anatomy 1
• Vertebral body metastases preferentially occur at sites of arterial convergence within the vertebral body center, where 4-5 vessels meet 4

Surgical Implications

• During thoracic aortic repair, sacrifice of intercostal arteries may be anatomically justified given the continuous anterior spinal artery, but preservation of lumbar arteries is prudent during extended thoracoabdominal repairs since the arteria radicularis magna most commonly arises from lumbar vessels 1
• The asymmetric and unpaired nature of lumbar veins increases risk of intraoperative vascular injury during retroperitoneal approaches 5
• Understanding that lumbar veins diverge closer to the iliocaval confluence is critical for avoiding hemorrhagic complications during anterior lumbar approaches 5