Internal carotid artery

At a glance

English

Internal carotid artery

Latin (TA2)

Carotis interna

System

Artery

Region

Head

Side

Paired, left and right

About the internal carotid artery

The internal carotid artery is one of the two terminal branches of the common carotid artery. The split usually happens near the upper border of the thyroid cartilage, at about the level of the third or fourth cervical vertebra. Its partner, the external carotid, serves the face and scalp, whereas the internal carotid is reserved for the brain, eye and orbit. Right at its start the vessel is slightly widened; this swelling, the carotid sinus, holds pressure receptors that help the body regulate blood pressure.

In the neck the artery climbs almost straight up inside the carotid sheath, with the internal jugular vein on its lateral side and the vagus nerve behind and between the two. It begins in the carotid triangle, just under the edge of sternocleidomastoid, and then passes deep to the parotid gland and the styloid muscles. Below the skull, the last four cranial nerves run between it and the jugular vein. The cervical part has no branches, which distinguishes it from the external carotid.

At the skull base the artery passes into the carotid canal of the petrous temporal bone, turns forwards and medially, and comes out above the foramen lacerum without truly passing through it. It then runs inside the cavernous sinus beside the body of the sphenoid, with the abducent nerve against its lateral side, and bends sharply up and back on itself in an S-shaped loop called the carotid siphon. Emerging medial to the anterior clinoid process, it pierces the dura, gives off the ophthalmic artery, and runs beside the optic nerve to its end below the anterior perforated substance.

Here it gives off the posterior communicating and anterior choroidal arteries, then divides into the anterior and middle cerebral arteries. Through the posterior communicating and anterior communicating arteries it joins the arterial circle at the base of the brain, which can carry blood around a blockage. Narrowing at the carotid bifurcation is a major cause of stroke and of brief attacks of visual loss in one eye. Aneurysms tend to form at its branching points, and a tear in the cavernous part can open a direct channel into the venous sinus. Neurosurgeons and radiologists usually name its course in seven numbered segments, C1 to C7.

Course and supply

Arises from

One of the two terminal branches of the common carotid artery, at the carotid bifurcation, usually at the level of C3 to C4.

Ends in

Ends below the anterior perforated substance by dividing into the anterior and middle cerebral arteries, after giving off the ophthalmic, posterior communicating and anterior choroidal arteries.

Supplies

Supplies most of the cerebral hemisphere on its side, the eye and orbit, the pituitary gland and parts of the forehead and nose through ophthalmic branches.