Corpus: Spinal canal

The spinal canal is the passageway formed by the vertebral arches and the back side of the vertebral bodies within the spinal column. The spinal cord and the cauda equina run through it.

The spinal canal extends from the large opening at the base of the skull (foramen magnum) through the cervical, thoracic, and lumbar spine, down to the sacral hiatus at the base of the spine. Its ventral wall is formed by the vertebral bodies and the intervertebral discs, while the lateral and dorsal walls are formed by the vertebral arches.

2.1. Ligaments

Two long, strong ligaments are located in the spinal canal:

• The posterior longitudinal ligament: at the front of the spinal canal, running along the vertebral bodies.
• The ligamentum flavum: at the back of the spinal canal, connecting one vertebral arch to the next.

Between the vertebrae are openings for the spinal nerves, the intervertebral foramina.

2.2. Spinal meninges

Like the brain, the spinal cord within the spinal canal is surrounded by specialized layers of tissue called meninges. The outermost layer is the periosteum, which is fused with the vertebrae and is also referred to as the outer layer (stratum periostale) of the spinal dura mater. Beneath this is the outer covering of the spinal cord, known as the meningeal layer (stratum meningeale) of the dura mater.

Below the dura mater is the arachnoid membrane (arachnoid mater), followed by the innermost layer, the pia mater, which directly covers the spinal cord.

The meningeal layer of the dura mater (the dura mater in the narrower sense) is often referred to clinically as the "dural sac."

2.3. Spinal canal spaces

Within the spinal canal, several spaces exist between the layers of the meninges:

• Epidural space: Located between the periosteum (outer layer) and the meningeal layer of the dura mater. This space contains fatty tissue and the epidural venous plexus.
• Subdural space: Found between the dura mater and the arachnoid mater. Normally, it only exists as a thin fissure.
• Subarachnoid space: Located between the arachnoid mater and the pia mater. This space is filled with cerebrospinal fluid (CSF).

The epidural space of the spinal canal is the target for procedures like epiduroscopy and epidural injections.

The subarachnoid space is used for procedures such as cerebrospinal fluid puncture (lumbar puncture) and myelography.