<aside>

Internal Carotid Artery (ICA) is a major paired artery that supplies blood to the brain, orbit, and part of the forehead. Here's a detailed overview:

</aside>

Overview

Aspect	Details
Origin	Bifurcation of the common carotid artery, usually at the level of C3–C4 vertebrae (upper border of thyroid cartilage)
Course	Ascends vertically in the neck (no branches in the cervical part), enters the skull via the carotid canal, passes through the cavernous sinus, and reaches the brain
Segments (Fischer Classification)	1. Cervical 2. Petrous 3. Lacerum 4. Cavernous 5. Clinoid 6. Ophthalmic (Supraclinoid) 7. Communicating
Branches	- Intracranial:

Ophthalmic artery
Posterior communicating artery
Anterior choroidal artery

Terminal branches: Anterior cerebral artery (ACA) Middle cerebral artery (MCA)

No branches in the neck | | Supply | - Anterior circulation of the brain

Eyes and orbit
Forehead and scalp (via ophthalmic artery branches) | | Imaging Landmarks | - Petrous ICA: within the temporal bone
Cavernous ICA: within cavernous sinus (S-shaped “carotid siphon”)
Supraclinoid ICA: gives rise to ACA & MCA | | Clinical Relevance | - ICA stenosis → risk for ischemic stroke - Carotid dissection → common cause of stroke in young adults
Aneurysms: especially in the cavernous or communicating segments
ICA injury during skull base trauma/surgery | | Circle of Willis Contribution | Forms part of the anterior circulation and gives off the posterior communicating artery to connect with the posterior circulation (vertebrobasilar system) |

Radiology

Gibo Classification

Cervical segment
Petrous segment
Supraclinoid segment
ICA terminus

Mandell, J. (2013). Core Radiology: A Visual Approach to Diagnostic Imaging. Cambridge: Cambridge University Press. doi:10.1017/CBO9781139225762

Bouthillier classification:

ICA segment	Extent	Branches	Supply
C1 (Cervical)	Extends from the carotid bifurcation to the skull base	No branches
C2 (Petrous)	Extends through the carotid canal and slightly past foramen lacerum	Caroticotympanic artery	Middle ear
		Vidian artery	“Artery of the pterygoid canal”
C3 (Lacerum)	Short segment that lies just above the foramen lacerum and extends from the petrous apex to the cavernous sinus	No branches
C4 (Cavernous)	Begins a series of back-and-forth bends historically called the "carotid siphon“	Meningohypophyseal trunk	Pituitary gland, tentorium, and clival dura
		Inferolateral trunk	Cranial nerves and CS dura.
C5 (Clinoid)
Short interdural segment that lies between the proximal and distal dural rings of the CS.
No branches

| | C6 (Ophthalmic) | First ICA segment that lies wholly within the subarachnoid space | Ophthalmic artery | Extensive anastomoses with ECA branches in and around the orbit and lacrimal gland | | | | Superior hypophyseal artery | Adenohypophysis and infundibular stalk as well as the optic chiasm | | C7 (Communicating) | Last ICA segment and extends from just below the PCoA origin to the terminal ICA bifurcation into the ACA and MCA. | Anterior cerebral artery (ACA) | | | | | Middle cerebral artery (MCA) | |

ICA+segments.png

Cavernous part sublcassification:

![‌ICA enter the Cavernous Sinus (CS) inferiorly at the level of the Petrolingual Ligament (PLL). Within the CS, it can be divided into five segments – (1) Posterior vertical segment (2) Posterior Genu [Posterior Bending] (3) Horizontal Segment (4) Anterior Genu [Anterior Bending] (5) Anterior Vertical. Blue area represents the Cavernous Sinus. MHT = Meningohypophseal Trunk, ILT = Inferolateral Trunk. Ant.= Anterior; Car. = Carotid; Clin. = Clinoid; Fiss. = Fissure; For. = Foramen; Impress. = Impression; Orb. = Orbital; Pet. = Petrous; Sup. = Superior; Trig. = Trigeminal.

Raj R, Smith V. Anatomical Basis of Clinical Manifestations Seen in Cavernous Sinus Syndrome: A Narrative Review. The Open Ophthalmology Journal. 2021;15(1). Accessed June 6, 2025. https://openophthalmologyjournal.com/VOLUME/15/PAGE/70/FULLTEXT/](attachment:d927dd79-24d1-441b-b363-692a4733d26a:TOOPHTJ-15-70_F5.jpg)

‌ICA enter the Cavernous Sinus (CS) inferiorly at the level of the Petrolingual Ligament (PLL). Within the CS, it can be divided into five segments – (1) Posterior vertical segment (2) Posterior Genu [Posterior Bending] (3) Horizontal Segment (4) Anterior Genu [Anterior Bending] (5) Anterior Vertical. Blue area represents the Cavernous Sinus. MHT = Meningohypophseal Trunk, ILT = Inferolateral Trunk. Ant.= Anterior; Car. = Carotid; Clin. = Clinoid; Fiss. = Fissure; For. = Foramen; Impress. = Impression; Orb. = Orbital; Pet. = Petrous; Sup. = Superior; Trig. = Trigeminal.