ICA Anatomy and Course

Overview

This lecture covers the anatomy and course of the internal carotid artery (ICA), discusses its segments and branches, and demonstrates how to visualize it using imaging techniques.

Course of the Internal Carotid Artery

• ICA originates from the bifurcation of the common carotid artery, posterior and medial to the external carotid.
• The left ICA comes directly from the left common carotid; the right ICA branches from the right common carotid after the brachiocephalic trunk.
• ICA ascends the neck, enters the skull through the carotid canal in the temporal bone, and travels toward the circle of Willis.
• The ICA runs adjacent to key anatomical landmarks: through the cavernous sinus, near the pituitary gland, and past the anterior clinoid process.
• At the circle of Willis, the ICA bifurcates into the anterior cerebral and middle cerebral arteries and gives off the posterior communicating artery.

Segments of the Internal Carotid Artery

• C1: Cervical segment—runs from bifurcation to the carotid canal, with no branches.
• C2: Petrous segment—within the carotid canal in the temporal bone; gives off caroticotympanic and vidian arteries.
• C3: Lacerum segment—crosses the foramen lacerum, no branches.
• C4: Cavernous segment—within the cavernous sinus; gives off inferior hypophyseal and meningeal arteries.
• C5: Clinoid segment—around the anterior clinoid process, no branches.
• C6: Ophthalmic segment—gives off ophthalmic and superior hypophyseal arteries.
• C7: Communicating segment—gives off posterior communicating and anterior choroidal arteries, then bifurcates into major cerebral arteries.

Important Branches of the ICA

• C2: Caroticotympanic and vidian arteries.
• C4: Inferior hypophyseal artery (to posterior pituitary) and meningeal artery (to anterior cranial meninges).
• C6: Ophthalmic artery (major supply to orbit) and superior hypophyseal artery (to anterior pituitary).
• C7: Posterior communicating and anterior choroidal arteries.

Imaging Techniques for ICA

• CT and MR angiogram provide detailed views of ICA’s course and branching.
• Digital subtraction angiography (DSA) is used for detailed vascular assessment, especially in suspected aneurysms or hemorrhage.

Key Terms & Definitions

• Internal carotid artery (ICA) — Major artery supplying blood to the brain.
• Carotid canal — Passage in the temporal bone through which ICA enters the skull.
• Cavernous sinus — Venous channel in the skull traversed by the ICA.
• Circle of Willis — Vascular ring at the base of the brain connecting major cerebral arteries.
• Anterior clinoid process — Bony landmark near ICA path.
• Ophthalmic artery — Branch of ICA supplying the orbit.
• Hypophyseal arteries — Vessels supplying the pituitary gland.

Action Items / Next Steps

• Review anatomy of skull base foramina for understanding ICA passage.
• Study the segments and main branches of the ICA.
• Practice identifying ICA segments and branches on imaging studies.