Functional Vascular Anatomy Important To The Interventionist

Arterial supply to the spine arises at segmental levels based on embryologic development of the somites. In the adult, arterial origins are variable based on the level of the spine. From the T3-5 to the L4 vertebral levels, segmental arteries arise from the thoracic or abdominal aorta. In the cervical region, supply to the segments is predominantly from the vertebral arteries as well as the ascending and deep cervical branches of the thyrocervical and costocervical trunks of the subclavian artery, respectively. The upper thoracic segmental supply is in balance between the uppermost segmental/intercostal branch of the aorta (the supreme intercostal) and the costocervical and thyrocervical trunk branches. At the skull base and in the upper cervical region supply can be from the occipital and ascending pharyngeal systems as well as from the posterior inferior cerebellar and vertebral arteries. Supply to the lower lumbosacral region including L5 and sacrum arises from iliolumbar, middle (median) sacral, and lateral sacral arteries of the distal aorta and internal iliac systems.

For most of the thoracic and lumbar spine, paired posterior segmental arteries arise from the posterolateral aorta and course from anterior to posterior along the vertebral body. Several small central branches pierce the cortical bone. Before continuing posterolaterally to join the neural structures to form the subcostal neurovascular bundle (intercostal artery), the dorsospinal artery arises medially. In the cervical and lower lumbosacral region where the arteries supplying the spine originate more laterally, the dorsospinal branch also arises near the neural foramen. The dorsal artery supplies adjacent osseous and soft tissue structures, while the more medial spinal artery courses into the foramen. The spinal artery gives rise to a posterior central branch with its superior and inferior division. These divisions meet with branches from adjacent vertebral bodies and with its counterpart from the opposite side to create a vascular anastamosis in the center of the posterior surface of the vertebral body. The spinal artery gives rise to a prelaminar artery, which follows the dorsal aspect of the vertebral canal, and to anterior and posterior radicular branches. These anterior and posterior radicular branches supply the ventral and dorsal nerve roots, respectively.

Supply to the spinal cord itself arises predominantly from the radicular arteries (Fig. 2). The anterior spinal artery is a midline artery that runs on the anterior surface of the cord and supplies the anterior two thirds of the cord including the deep "medullary" portion containing the primary motor fibers. An arterial "pial" plexus that encompasses the posterior one third of the cord supplies the posterior cord. Radicular arteries supplying the anterior spinal artery are called radiculomedullary arteries. Radicular arteries supplying the posterior spinal plexus are called radiculopial arteries. The number and location of feeding radicular branches are highly variable in any individual. There are roughly two to four, two to three, and zero to four cervical, thoracic, and lumbosacral radicu\omedullary arteries, respectively. There are three to four, six to nine, and zero to three cervical, thoracic, and lumbosacral radiculop'al arteries, respectively. The dominant supply of the lower anterior thoracic cord is the artery of Adamkiewicz or artery of lumbar enlargement, which arises 85% of the time from the left T9-L2 radicular branches. But because it can arise from T4-L2 or L3, it is imperative to exclude its presence at a potential embolization site. The dominant supply to the cervical anterior spinal artery is the artery of cervical enlargement, which arises from either right or left midcervical vertebral artery.

The cord parenchyma drains into anterior and posterior spinal veins, which run the surface of the cord. At some levels, these join the anterior and posterior radicular veins on the exiting roots and coalesce to join the foraminal intervertebral vein. The majority of the venous drainage of the vertebral body is into the anterior internal (epidural) venous plexus along the posterior margin of the vertebral body. The anterior (epidural) plexus, with the smaller posterior internal (epidural) plexus along the anterior margin of the posterior elements, drain into the intervertebral vein exiting the neural foramen. Drainage then is into the posterior intercostal, superior intercostal, and subcostal veins. From there, drainage is into the innominate vein and azygos system depending on the level.

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