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Carotid Overview

Overview of Major Regions Supplied

  • optic nerves and retina 
  • cortex and deep white matter of the frontal and parietal lobes and lateral aspects of the temporal and occipital lobes 
  • all of the corpus callosum except its posterior regions
  • most of the basal ganglia and internal capsule 

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Course of the carotid arteries and formation of major branches

The right common carotid artery originates from the bifurcation of the brachiocephalic trunk, while the left common carotid originates directly from the aortic arch. Each common carotid then branches to form the internal and external carotid vessels. After the internal carotid ascends through the neck, traverses the temporal bone, and passes through the cavernous sinus, it finally reaches the subarachnoid space at the base of the brain.

As the internal carotid leaves the cavernous sinus, it gives rise to its first intracranial branch, the ophthalmic artery, which travels along the optic nerve into the orbit. There its branches supply the retina and other structures of the eyeball itself, as well as other structures in and around the orbit. The internal carotid continues in a superior direction and usually gives off two additional branches: the posterior communicating artery and anterior choroidal artery.

The posterior communicating arteries usually link the internal carotid to the posterior cerebral artery (PCA), and may be either large or threadlike. However, in a number of individuals one or both of the posterior cerebral arteries retain their embryological state as direct branches of the internal carotid artery itself. The anterior choroidal artery also varies a great deal in size and importance in different individuals, and may branch from the middle cerebral artery rather than the internal carotid. For this reason, we will discuss it when we cover the middle cerebral artery (MCA). Finally, the internal carotid divides to form the anterior cerebral artery (ACA) and middle cerebral artery.

Clinical Note:

There is a tendency for atheromatous plaques to form at branchings and curves of the cerebral arteries.  Thus in the carotid circulation the most frequent sites are: in the internal carotid artery at its origin from the common carotid, in the stem MCA or its bifurcation into superior and inferior divisions, and in the ACA as it curves backwards over the corpus callosum.