Internal Carotid Artery

Overview

The internal carotid artery (ICA) is a major branch of the common carotid artery, supplying the head and brain, located bilaterally in the neck.

Origin

• Arises at bifurcation common carotid artery at the level of the upper border of the thyroid cartilage (level of C4). 
• Commences with a slight bulge, the carotid sinus (containing baroreceptors supplied by glossopharyngeal and vagus nerves).

Segments & Course

C1 – Cervical

• Commences from common carotid bifurcation, the ICA ascends vertically within the carotid sheath – anterior to the transverse process of C1-C3
• Enter the base of skull via the carotid canal of the petrous temporal bone

C2 – Petrous

• Bends anteromedially then passes horizontally to the foramen lacerum

C3 – Lacerum

• From the foramen lacerum (does not pass through), curves upwards to enter the cavernous sinus through the petrolingual ligament

C4 – Cavernous

• Commences at the petrolingual ligament and has a curve in its course within the cavernous sinus (carotid siphon)
• Extends to the proximal dural ring (formed by medial and inferior periosteum of the anterior clinoid process)

C5 – Clinoid

• From proximal dural ring to the distal dural ring

C6 – Ophthalmic

• From distal dural ring, courses horizontally and parallel to the optic nerve, to the origin of posterior communicating artery

C7 – Communicating

• Passes between the optic and oculomotor nerves to the anterior perforated substance at the medial extremity of the lateral cerebral fissure before terminating as the anterior cerebral and middle cerebral artery

Termination

Anterior cerebral and middle cerebral artery

Branches

• C1: Cervical segment – none
• C2: Petrous (horizontal) segment
  • Caroticotympanic artery
  • Vidian artery
• C3: Lacerum segment – none
• C4: cavernous segment
  • Meningohypophyseal trunk
  • Inferolateral trunk
  • Capsular arteries (of McConnell) (variable)
• C5: Clinoid segment – none
• C6: Ophthalmic (supraclinoid) segment
  • Ophthalmic artery
  • Superior hypophyseal artery
• C7: communicating segment
  • Posterior communicating artery
  • Anterior choroidal artery
  • Anterior cerebral artery
  • Middle cerebral artery

Arterial Supply

• Vasovasorum – small network of capillaries supplying the lumen and walls of large blood vessels

Relations

• Lateral to external carotid at its origin, but ascends more posteriorly, medially and deeper within the carotid sheath (beside the pharynx) to the carotid canal in the base of the skull.
• Anterior to sympathetic trunk, pharyngeal veins and superior laryngeal branch of the vagus nerve
• Lateral to ascending pharyngeal artery
• Medial to internal jugular vein

C1

• Posterior: longus capitis, superior cervical ganglion of the sympathetic trunk, superior laryngeal branch of vagus nerve
• Medial: pharynx and ascending pharyngeal artery
• Lateral: internal jugular vein and vagus nerve
• Anterior:
  • Inferior: lingual vein, facial vein, occipital artery, and hypoglossal nerve
  • Superior: separate from ECA by styloglossus, stylopharyngeus, tip of styloid process and stylohyoid ligament, glossopharyngeal nerve and pharyngeal branch of vagus nerve

Variant Anatomy

• Aberrant ICA (enlargement of caroticotympanic/hyoid artery which anastomoses with inferior tympanic artery from ECA, when cervical ICA is hypoplastic/absent)
• Absent ICA
• Retropharyngeal ICA
• Kissing carotids
• Persistent carotid-vertebrobasilar anastomsoes
• Lateralised ICA

Clinical significance

Surgically accessed via incision along anterior border of sternocleidomastoid.

A single artery supplying part of the posterior circulation of the brain.