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//VASCULAR SUPPLY OF SPINAL CORD, ROOTS AND NERVES

VASCULAR SUPPLY OF SPINAL CORD, ROOTS AND NERVES

ARTERIES

The spinal cord, its roots and nerves are supplied with blood by both longitudinal and segmental vessels (Fig. 43.9). Three major longitudinal vessels, a single anterior and two posterior spinal arteries (each of which is sometimes doubled to pass on either side of the dorsal rootlets), originate intracranially from the vertebral artery and terminate in a plexus around the conus medullaris. The anterior spinal artery forms from the fused anterior spinal branches of the vertebral artery, and descends in the anterior median fissure of the cord. Each posterior spinal artery originates either directly from the ipsilateral vertebral artery or from its posterior inferior cerebellar branch, and descends in a posterolateral sulcus of the cord. The segmental arteries are derived in craniocaudal sequence from spinal branches of the vertebral, deep cervical, intercostal and lumbar arteries. These vessels enter the vertebral canal through the intervertebral foramina and anastomose with branches of the longitudinal vessels to form a pial plexus on the surface of the cord. The segmental spinal arteries send anterior and posterior radicular branches to the spinal cord along the ventral and dorsal roots. Most anterior radicular arteries are small, and end in the ventral nerve roots or in the pial plexus of the cord. The small posterior radicular arteries also supply the dorsal root ganglia: branches enter at both ganglionic poles to be distributed around ganglion cells and nerve fibres. (See also Crock 1996.)

  

Fig. 43.9  Arteries of the spinal cord.
(Reprinted from Netter Anatomy Illustration Collection, © Elsevier Inc. All Rights Reserved.)

Segmental medullary feeder arteries

Some radicular arteries, mainly situated in the lower cervical, lower thoracic and upper lumbar regions, are large enough to reach the anterior median sulcus where they divide into slender ascending and large descending branches. These are the anterior medullary feeder arteries (Dommisse 1975). They anastomose with the anterior spinal arteries to form a single or partly double longitudinal vessel of uneven calibre along the anterior median sulcus. The largest anterior medullary feeder, the great anterior segmental medullary artery of Adamkiewicz, varies in level, arising from a spinal branch of either one of the lower posterior intercostal arteries (T9–11), or of the subcostal artery (T12), or less frequently of the upper lumbar arteries (L1 and L2). It most often arises on the left side (Carmichael & Gloviczki 1999). Reaching the spinal cord, it sends a branch to the anterior spinal artery below and another to anastomose with the ramus of the posterior spinal artery which lies anterior to the dorsal roots. It may be the main supply to the lower two-thirds of the cord. Central branches of the anterior spinal artery enter the anterior median fissure, and then turn right or left to supply the ventral grey column, the base of the dorsal grey column, including the dorsal nucleus, and the adjacent white matter (Fig. 43.9).

Each posterior spinal artery contributes to a pair of longitudinal anastomotic channels, anterior and posterior to the dorsal spinal roots. These are reinforced by posterior medullary feeders from the posterior radicular arteries. The latter are variable in number and size, but smaller, more numerous and more evenly distributed than the anterior medullary feeders. The anterior channel is joined by a ramus from the descending branch of the great anterior segmental medullary artery of Adamkiewicz. In all longitudinal spinal arteries the width of the lumen is uneven, and complete interruptions may occur. At the conus medullaris they communicate by anastomotic loops. Anastomoses other than those between the pial or peripheral spinal arterial branches may be important, e.g. a posterior spinal series of anastomoses between rami of the dorsal divisions of segmental arteries near the spinous processes.

Intramedullary arteries

The central branches of the anterior spinal artery supply about two-thirds of the cross-sectional area of the cord. The rest of the dorsal grey and white columns and peripheral parts of the lateral and ventral white columns are supplied by numerous small radial vessels which branch from posterior spinal arteries and the pial plexus. In a microangiographic study of the human cervical spinal cord, up to six anterior, and eight posterior, radicular spinal arteries were described, and up to eight central branches arose from each centimetre of the anterior spinal artery (Turnbull et al 1966).

Spinal cord ischaemia

The spinal cord can rely neither for its transverse nor for its longitudinal blood supply entirely on the longitudinal arteries. The anterior longitudinal artery and the intramedullary arteries are functional endarteries, although overlap of territories of supply has been described. Damage to the anterior longitudinal artery can result in loss of function of the anterior two-thirds of the cord. The longitudinal arteries cannot supply the whole length of the cord, and the input of the segmental medullary feeder vessels is essential. This is especially true of the artery of Adamkiewicz (great anterior segmental medullary artery), which may effectively carry the major supply for the lower cord. The midthoracic cord, distant from the main anterior medullary feeders, is particularly liable to become ischaemic after periods of hypotension.

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