Spinal dura mater
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The spinal dura mater is a fibrous, non-adherent, tough layer surrounding the spinal cord. Unlike the intracranial dura mater, it only has a single layer which is continuous with the inner (meningeal) layer of the intracranial dura at the foramen magnum. It is separated from the wall of the vertebral canal by the epidural space. This space contains loose areolar tissue and a network of internal vertebral venous plexuses. The subdural space separates the spinal dura mater from the arachnoid mater. Both membranes are in direct contact with each other, apart from a small amount of fluid which lubricates the opposing surfaces 1.
The spinal dura mater is attached to the circumferential base of the foramen magnum and also to the second and third cervical vertebra. It extends to the level of S3 2. Distal to this, it blends in with the periosteum to form a thin layer surrounding the filum terminale. It is anchored firmly to the posterior base of the coccyx via the periosteum.
The spinal dura mater consists of parallel longitudinally oriented fibrous and elastic bands 1. Internally it is covered by mesothelium and supplied by few blood vessels.
The blood supply to the spinal dura mater is primarily derived from the anterior and posterior radicular arteries as they anastamose with one anterior and two posterior spinal arteries1. The segmental arteries themselves originate from a variety of sources depending on which level they supply (see spinal cord blood supply).
The largest of these segmental arteries and the dominant supplying artery to the thoracolumbar spinal cord is the artery of Adamkiewicz which has a variable origin 1.
The venous drainage principally follows the arterial supply. The anterior and posterior spinal veins drain into the segmental veins. The major addition is the internal vertebral venous plexus which lies in the epidural space of the vertebral canal and drains the external surface of the dura mater 3.
The spinal dura mater is innervated by sensory fibers of the meningeal branches of each spinal nerve. These fibers branch off from each spinal nerve near the bifurcation of the ventral and dorsal rami, usually proximally to the grey and white rami communicantes. The fibers then pass through the intervertebral foramen.
In addition to supplying the meninges of the spinal cord, these meningeal branches also supply the annulus fibrosus of the intervertebral disc and the facet joints amongst other structures1.