What is Inside the Vertebral Canal?
The canal space is lined with periosteum. It encloses the spinal cord (42–46 cm long and 10–14 mm in diameter), which in adults terminates at the level of the first or second lumbar vertebra (L1–L2).
Structural layers and spaces within the canal from superficial to deep:
- Epidural space (spatium epidurale) — located between the periosteum and the dura mater. It contains adipose tissue and the internal vertebral venous plexus.
- Dura mater (dura mater spinalis).
- Arachnoid mater (arachnoidea mater spinalis).
- Subarachnoid space (spatium subarachnoideum) — located between the arachnoid and pia mater.
- Pia mater (pia mater spinalis) — tightly adheres to the spinal cord. Its specialization is the denticulate ligament (ligamentum denticulatum), which anchors the spinal cord within the canal.
Blood Supply and Venous Drainage
Inside the vertebral canal (canalis vertebralis), external to the dura mater, lie the internal vertebral venous plexuses (plexus venosi vertebrales interni). They extend from the foramen magnum to the lower end of the sacral canal and are divided into anterior and posterior plexuses. The anterior internal plexus receives basivertebral veins originating from the vertebral bodies. The internal plexuses anastomose with the external ones.
Arterial blood supply is provided by radicular arteries (aa. radiculares), which enter the vertebral canal alongside the anterior and posterior spinal nerve roots. Because the spinal cord grows more slowly than the vertebral column during embryogenesis (ascensus medullae spinalis), the level at which the artery penetrates the spinal cord lies higher than its origin from the aorta. This accounts for the oblique (ascending) course of the arteries within the canal.
Innervation of Canal Structures
The meninges and tissues of the canal itself are innervated by the meningeal branch (r. meningeus). It branches off the spinal nerve, loops back into the vertebral canal, and innervates:
- The dura mater;
- The periosteum;
- Blood vessels, as it contains sympathetic fibers.
Clinical Significance
Space-occupying lesions in the vertebral canal lead to compression of neural structures:
- Intervertebral disc herniation: extrusion of a free fragment (sequestration) into the canal causes massive compression. At the lumbar level, this results in cauda equina syndrome, manifested by lower paraparesis, sensory loss in the saddle/anogenital region, and overflow incontinence.
- Tumors: can be extradural or intradural. Schwannomas often grow in a "dumbbell" shape—originating in the intervertebral foramen and growing bidirectionally: inside and outside the canal. Lateral spinal cord compression leads to Brown-Séquard syndrome. Advanced skin cancers (such as T4/T4b stages) may also invade the epidural space of the canal.
- Tonsillar herniation: in space-occupying processes of the posterior cranial fossa, the cerebellar tonsils may shift downward through the foramen magnum into the vertebral canal, compressing the caudal brainstem.