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ANATOMY FOR DIAGNOSTIC IMAGING
The dura mater is a loose sheath around the spinal cord representing the inner layer of the cerebral dura. The outer periosteal layer is represented by the periosteum of the vertebral bodies with the extradural - or epidural - space between these layers. The extradural (epidural) space contains loose areolar tissue, fat and a plexus of veins. It extends laterally for a short distance beyond the intervertebral foramina along the spinal nerves. The dural sac or thecal sac extends inferiorly as far as the S2 vertebral level. Below this the arachnoid and dura blend with the pia on the filum terminale. THE BLOOD SUPPLY OF THE SPINAL CORD (Figs 3. 17 and 3. 18) The spinal cord is supplied by two posterolateral spinal arteries that supply the posterior white columns and part of the grey matter of the dorsal horns, and a single midline anterior spinal artery that supplies the remainder (i. e. twothirds of the cross-sectional area) of the spinal cord. At the lower end of the cord (i. e. the conus) the anterior artery divides in two and anastomoses with each posterior spinal artery. A small 'twig' continues on the filum terminale. The posterolateral spinal arteries arise by one or two branches on each side from the vertebral artery or, more commonly, its posterior inferior cerebellar branch. The anterior spinal artery also arises from the vertebral artery by union, in the midline, of a branch from each side. These arteries receive further supply at intervals along the length of the cord from branches of the deep cervical branch of the subclavian artery, the cervical part of the vertebral artery, and by branches from the intercostal and first lumbar arteries. These segmental branches pass into the intervertebral foramen and along the nerve roots towards the spinal cord.
Fig. 3. 17 Arterial supply of the spinal cord.
