Internal Carotid Artery

Origin · Bouthillier C1–C7 segments · branches · skull-base and angiographic landmarks

Reference Images

Color-coded Bouthillier ICA segments on MRA — Bouthillier Segments on MRAClick to enlarge

Supraclinoid ICA branches — Supraclinoid ICAClick to enlarge

ICA segments table — C1–C7 SummaryClick to enlarge

Petrolingual ligament and ICA segments — Petrolingual LigamentClick to enlarge

ICA course anatomy — Carotid CourseClick to enlarge

Cavernous ICA and dural rings — Cavernous ICA & Dural RingsClick to enlarge

Foramen lacerum pearl — Foramen Lacerum PearlClick to enlarge

Foramen lacerum on CT and skull diagram — Foramen Lacerum LocalizationClick to enlarge

Angiographic ICA branches by segment — Branches by SegmentClick to enlarge

Cavernous and supraclinoid branches — Cavernous & Supraclinoid BranchesClick to enlarge

At a Glance

Origin and terminationThe ICA begins at the common carotid bifurcation, enters the skull through the carotid canal, and terminates as the ACA and MCA.

Carotid bulb

The proximal ICA expands at the carotid sinus. The carotid body is an adjacent chemoreceptor organ.

Bifurcation level

Usually near C3–C5, the hyoid, or upper thyroid cartilage; high, low, and asymmetric bifurcations occur.

Function

Major anterior-circulation supply to the brain and orbit.

C1–C3: Skull-Base Entry

C1 Cervical

Bifurcation to carotid canal; ascends in the carotid sheath and is usually branchless.

C2 Petrous

Traverses the petrous carotid canal and turns anteromedially at the petrous genu. Branches: caroticotympanic and Vidian arteries.

C3 Lacerum

Short segment above the foramen lacerum, ending at the petrolingual ligament; usually branchless.

Key pearlThe ICA passes over the fibrocartilage-filled foramen lacerum—it does not traverse the foramen.

C4–C7: Intracranial Course

C4 Cavernous

Petrolingual ligament to proximal dural ring through the cavernous sinus. CN VI lies lateral. Branches: MHT and inferolateral trunk.

C5 Clinoid

Very short, usually branchless segment between the proximal and distal dural rings.

C6 Ophthalmic

Intradural supraclinoid segment giving ophthalmic and superior hypophyseal arteries.

C7 Communicating

Gives PCOM and AChA, then divides into ACA and MCA.

Branches by Segment

Even segments

C2: caroticotympanic; Vidian.
C4: meningohypophyseal trunk; inferolateral trunk.
C6: ophthalmic; superior hypophyseal.

Terminal segment

C7 side branches: PCOM and AChA.
C7 terminal branches: ACA and MCA.

PatternOdd segments are usually branchless except C7; C2, C4, and C6 characteristically have paired branch groups.

Branch Mnemonics

A VIP'S COMMA

Anterior choroidal
Vidian
Inferolateral trunk
Posterior communicating
Superior hypophyseal
Caroticotympanic
Ophthalmic
Meningohypophyseal trunk
Middle cerebral
Anterior cerebral

In segment order

Calming Voices Make Intra-Operative Surgery Pleasurable And Almost Memorable

C2: C/V · C4: M/I · C6: O/S · C7: P/A/A/M.

Imaging & Reporting Pearls

Use segment names

Describe pathology by Bouthillier segment and relationship to the cavernous sinus and dural rings. “Paraclinoid” generally spans C5–C6 but is less specific.

Carotid siphon

Commonly refers to the curved lacerum, cavernous, clinoid, and adjacent supraclinoid course.

Dural rings

The distal dural ring marks entry into the subarachnoid space and helps determine whether disease is intra- or extradural.

Other schemes

Older Gibo, four-part Terminologia Anatomica, and angiographic schemes remain in use; state the classification if terminology is ambiguous.