The intrinsic venous drainage of the spinal cord consists of equally distributed radial veins draining into a pial venous plexus. Anastomosing channels drain the venous blood into radicular veins which usually (60%) penetrate the dura with the nerve roots. The remainder penetrate the dura separately. There are no valves between the spinal cord and the dura. The veins play a key role in the balance of spinal tissue perfusion, and it is the venous component of vascular malformations that usually cause symptoms.
The radicular veins drain into the lateral confluence of epidural veins. In the cervical region, the vertebral veins drain into the suboccipital venous system, the internal jugular and the deep cervical veins. The thoracic veins drain into the azygous and hemiazygous systems. The lumbar veins drain into the inferior vena cava and left renal vein, and the sacral veins drain into the internal iliac veins. These systems form an almost continuous bilateral paraspinous axis.
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