Overview

Neck and skull base. The ICA starts at the carotid bifurcation and ascends in the carotid sheath, deep to the parotid region and the styloid muscles, to the skull base. It enters the carotid canal in the petrous part of the temporal bone and runs forward and medially through it. It then passes above (not through) the foramen lacerum.

Cavernous sinus. The artery next enters the cavernous sinus. Inside the sinus it forms an S-shaped bend, the carotid siphon, with the abducens nerve (CN VI) lying beside it. The oculomotor, trochlear and ophthalmic and maxillary trigeminal nerves (CN III, IV, V1 and V2) run in the sinus's lateral wall.

Intracranial course. The artery pierces the dura next to the anterior clinoid process. It gives off the ophthalmic artery, then the posterior communicating and anterior choroidal arteries. Lateral to the optic chiasm it divides into the anterior and middle cerebral arteries.

Segments. Neurosurgeons and radiologists number its segments C1–C7: cervical, petrous, lacerum, cavernous, clinoid, ophthalmic and communicating.

Anatomy

Course: It runs from the carotid bifurcation (C3–C4) through the carotid canal and the cavernous sinus, then through the dura beside the anterior clinoid process to its termination beside the optic chiasm.
Branches: There are no branches in the neck. Small branches in the petrous and cavernous parts supply the pituitary and the dura. The main intracranial branches are the ophthalmic artery (which gives the central retinal artery), the posterior communicating artery and the anterior choroidal artery. It ends as the anterior and middle cerebral arteries.

Function

Supplies most of the cerebral hemisphere, including the frontal, parietal and much of the temporal lobes, plus the internal capsule and basal ganglia.
Supplies the orbit and retina through the ophthalmic artery.
Forms the anterior part of the circle of Willis.

Clinical significance

Amaurosis fugax and ICA stenosis

Emboli from an ICA plaque can block the central retinal artery and cause temporary loss of vision in one eye, often described as a curtain coming down. The same plaque can cause a stroke in the territory of the middle cerebral artery.

Carotid dissection

A tear in the wall of the ICA is an important cause of stroke in young adults. It typically causes neck pain and headache with a partial Horner syndrome, because sympathetic fibres run along the artery.

Carotid–cavernous fistula and PCom aneurysm

A rupture of the ICA into the cavernous sinus (a carotid–cavernous fistula) causes a pulsating, protruding eye, conjunctival swelling, a bruit and a CN VI palsy. An aneurysm where the posterior communicating artery leaves the ICA presses on CN III and causes a painful third nerve palsy with a dilated pupil.

Compiled from standard anatomy and physiology references — see the Cardiovascular System sources. For education only; not medical advice.