The anterior spinal artery supplies the anterior portion of the spinal cord and arises from the vertebral artery (V4, intradural segment) in the region of the medulla oblongata. The two vertebral arteries (one of which is usually bigger than the other) anastomose in the midline to form a single anterior spinal artery at the level of the foramen magnum.
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Gross anatomy
It descends along the anterior surface of the spinal cord, within the anterior median fissure and is covered by pia mater, which creates a sheath (linea splendens). Along its course, it is reinforced by other branches that enter the spinal canal via the intervertebral foraminae. Although communication exists at multiple levels, the supply of the cord can be thought of as occurring in three relatively separate sections, supplied by somewhat predictable feeders 4.
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C1-T3
anterior segmental medullary arteries (branches of the vertebral artery) at ~C3
ascending cervical artery (the branch of the inferior thyroid artery) at ~C6-7
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T3-7
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T8-conus
artery of Adamkiewicz, usually between T9 and T12
cone artery, a.k.a. artery of Desproges-Gotteron - a branch arising from the iliolumbar arteries
The anterior spinal artery communicates sporadically with the posterior spinal arteries via a pial plexus that encases the cord. At most levels it gives off a sulcal artery which enters the anterior median fissure.
It terminates inferiorly by forming the cruciate anastomosis of the conus medullaris with the posterior spinal arteries 5.
Variant anatomy
Variation of the anterior spinal artery origin include 6:
duplication, or two independent anterior spinal arteries
single origin of anterior spinal artery from unilateral vertebral artery
single or duplicate anterior spinal arteries arising off vascular arcade between vertebral arteries