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Internal carotid artery

The internal carotid artery (ICA) is a major blood vessel that supplies oxygenated blood to significant portions of the brain, eyes, and some structures of the face. It is one of the two terminal branches of the common carotid artery, the other being the external carotid artery. The ICA is essential for cerebral perfusion and forms a critical component of the Circle of Willis, providing collateral blood flow to the brain. Its anatomical course, relationships, and imaging characteristics are fundamental for clinicians, especially in the context of stroke, aneurysms, and vascular malformations.

Synonyms:

  • ICA

  • Internal carotid

  • Arteria carotis interna (Latin)

  • Cerebral carotid artery (informal)

Origin and Course:

  • The ICA originates at the bifurcation of the common carotid artery, typically at the level of the C3–C4 vertebral bodies (upper border of the thyroid cartilage).

  • The artery ascends vertically in the neck without branching in the cervical portion.

  • It enters the skull through the carotid canal in the petrous part of the temporal bone.

  • The ICA then passes through four segments:

    • Cervical segment: Ascends in the neck within the carotid sheath, lateral to the pharynx.

    • Petrous segment: Passes within the petrous part of the temporal bone.

    • Cavernous segment: Runs through the cavernous sinus, alongside cranial nerves III, IV, V1, V2, and VI.

    • Cerebral (supraclinoid) segment: Emerges into the subarachnoid space, giving off ophthalmic, posterior communicating, anterior choroidal, and terminal branches (anterior and middle cerebral arteries).

  • The ICA does not give off any branches in the neck (cervical segment).

Function:

  • Supplies blood to the anterior part of the brain, including the frontal, parietal, and superior temporal lobes.

  • Provides blood to the eyes via the ophthalmic artery.

  • Supplies parts of the pituitary gland, orbit, and forehead.

MRI Appearance:

  • On MR Angiography (MRA), the ICA appears as a well-defined, high-signal tubular structure following its anatomical course, from the neck into the skull.

  • Flow-voids are seen in standard T1- and T2-weighted images, corresponding to the fast-flowing blood within the vessel.

  • Pathology such as dissection, aneurysm, or stenosis may be identified as changes in vessel caliber, irregular walls, or signal voids.

CT Appearance:

  • On CT Angiography (CTA), the ICA is visualized as an opacified, contrast-filled vessel, following its anatomical pathway.

  • Bony landmarks, such as the carotid canal, help identify the petrous segment.

  • Calcifications, stenosis, or vessel occlusion can be identified on non-contrast or contrast-enhanced scans.

  • The ICA can be distinguished from the external carotid artery based on its vertical ascent and lack of cervical branches.

MRI images

Internal carotid artery MRI TOF axial image

CT images

Internal carotid artery ct axial images

CT images

Internal carotid artery ct sagittal images

CT image

Internal carotid artery CT axial image-img-00000-00000