Paired vertebral arteries provide blood supply for the upper part of the spinal cord, brainstem, cerebellum, and posterior part of the brain. Each artery originates from the first part of the subclavian artery, it then courses superiorly along the sides of the neck, merging with its companion at the pons level to form the single, midline basilar artery.
Basilar and internal carotid arteries give off multiple communicating branches which anastomose with each other at the base of the brain, forming the hexagonal vascular network called the circle of Willis. The circle of Willis connects the anterior and posterior brain circulations. This reflects the importance of the vertebral artery for the human organism.
|Preforaminal (from subclavian artery to transverse foramen of C6)
Foraminal (through the transverse foramina of C6 to C2)
Extradural (from the transverse foramen of axis to the vertebral canal)
Intradural (from the vertebral canal to the inferior border of pons)
|Anterior spinal, posterior spinal, posterior inferior cerebellar, meningeal, medullary, basilar arteries
This article will discuss the anatomy, segments and branches of the vertebral artery, as well as most frequent, life-threatening clinical condition related to it.
- Clinical relations
There are four segments of the vertebral artery, following its way through the neck; preforaminal, foraminal, extradural (atlantic), and intradural (intracranial) parts.
The vertebral artery originates from the first part of the subclavian artery, then extends superiorly and posteriorly, passing between the longus colli and the anterior scalene muscles.
Anterior to it are the vertebral and internal jugular veins, while posteriorly, there are the transverse process of C7 vertebra, the sympathetic trunk, and the superior cervical ganglion.
After passing between the longus colli and anterior scalene muscles, the vertebral artery runs superiorly through the transverse foramina of the C6 to C2 vertebrae. It pursues an almost vertical course as far as the transverse process of the axis (C2).
While passing through the transverse foramina, the vertebral artery is located anterior to the trunks of the cervical spinal nerves. Also, it is surrounded by the venous plexus, which form the vertebral vein at the lower part of the neck.
Extradural (atlantic) segment
This segment begins after the artery passes through the transverse foramen of the axis (C2) where it is subdivided into two parts; vertical and horizontal:
- Vertical part courses superiorly, crossing the root of the C2 spinal nerve and entering the transverse foramen of the atlas (C1).
- After passing through the transverse foramen of atlas, the horizontal part begins. The artery curves medially and posteriorly, passing behind the superior articular process of the atlas and reaches the groove on the upper surface of the posterior arch of the atlas. From there, it passes under the posterior atlantooccipital membrane and enters the vertebral canal. The horizontal part is contained in the occipital triangle.
Learn more about the triangles of the neck, including the occipital triangle here.
Intradural (intracranial) part
After entering the vertebral canal, the vertebral artery pierces the dura mater and courses superiorly over the anterior surface of the medulla oblongata. At the lower border of the pons, it merges with the opposite vertebral artery and forms the basilar artery. The basilar artery ascends along the ventral surface of the pons in its basilar groove within the pontine cistern. The vessel terminates as it bifurcates into two posterior cerebral arteries.
Along its course, the vertebral artery gives rise to the following branches:
- Anterior spinal artery from its intradural segment. This artery originates from two smaller vessels from each vertebral artery which unite around the intradural segment. The anterior spinal artery then passes through the foramen magnum and descends along the anterior aspect of the spinal cord, supplying its anterior portion.
- May give off the posterior spinal artery; although this vessel usually arises from the posterior inferior cerebellar artery.
- Posterior inferior cerebellar artery originates from each vertebral arteries’ intracranial segment and supplies the cerebellum.
- Meningeal branches from its intracranial part near the foramen magnum, for supplying the meninges.
- Medullary arteries from its intracranial part that supply the medulla oblongata.
The terminating branch of the vertebral artery is the basilar artery. The basilar artery contributes to the circle of Willis. It terminates by bifurcating into two posterior cerebral arteries. Each of these gives off the posterior communicating artery, which anastomoses with the middle cerebral artery, a branch of the internal carotid artery. This is how the communication between vertebral and internal carotid arteries is established.
Test your knowledge on the arteries of the vertebral column with this quiz.
The vascular network of the posterior circulation made by vertebral arteries is susceptible to ischemic and hemorrhagic insults that can result in a cerebrovascular accident (stroke). Since vertebral and basilar arteries mostly contribute to vascularization of the brainstem, it will be the most severely affected.
Cerebrovascular incidents (ischemic) are usually caused by a thrombus that occludes the arterial lumen and blocks the blood flow to the target tissue. In a lack of arterial blood, the tissue undergoes ischemia, which, eventually leads to its necrosis (infarction).
Usually occlusions happen within the small perforating branches which supply the medulla oblongata, pons or mesencephalon. Brainstem infarction leads to dysfunction of the cranial nerves. The cranial nerves do not decussate, except for the CN II, CN IV, CN VII and CN XII. That means if a lesion affects the nuclei of the remainder of the cranial nerves, it will manifest either as the sensation loss or atrophy of the muscle of the same side as the place of the infarction.
One of the common syndromes that occur during mesencephalon infarctions is the Weber syndrome, in which the infractions affect the nuclei of the oculomotor nerve. The symptoms are the drop of the upper eyelid (ptosis) at the same side, with hemiplegia or hemiparesis of the contralateral side of the body, due to the damage of the fibers of the corticospinal pathway before they decussate.
Infarction in the pons causes the Millard-Gubler syndrome, which manifests as the ipsilateral paralysis of the mimic musculature (due to affection of the nuclei of CN VII) and contralateral hemiparesis/hemiplegia (damage of the corticospinal tract).
If the infarction is in the medulla oblongata, it will cause the Wallenberg syndrome, which consists of the ipsilateral paresis of the soft palate with dysphagia (due to affection of the nucleus ambiguus), ipsilateral ataxia of the limbs (due to affection of the inferior cerebellar peduncle), ipsilateral deficit in pain and temperature sensation of the face (due to affection of the spinal trigeminal nucleus), and contralateral deficit in pain and temperature sensation of the body (due to the damage of the lateral spinothalamic tract).
Stroke is one of the most urgent conditions in medicine. The therapy consists in recanalization of the occluded vessel, either by pharmacotherapy or with endovascular intervention. After that, neuroprotective therapy is indicated, with subsequent therapy for secondary prevention of another stroke.
Prevention is based on three principles:
- Control the risk factors, such as arterial hypertension, diabetes mellitus, hyperlipidemia, alcohol consuming and smoking
- Apply anticoagulant therapy with medications such as acetylsalicylic acid
- Surgical treatment
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