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Internal carotid artery

Radswiki and Dr Jeremy Jones et al.

The internal carotid artery is a terminal branch of the common carotid artery. It arises most frequently between C3 and C5 where the common carotid bifurcates to form the internal carotid and the external carotid artery (ECA).

Variations in origin

Level of bifurcation

Although the majority arise between C3 and C5 a wide variation exists.

C1 - 2 : 0.3%
C2 - 3 : 3.7%
C3 - 4 : 34.2%
C4 - 5 : 48.1%
C5 - 6 : 13%
C6 - 7 : 0.15%

Asymmetry

In one study (Smith, D and Larsen JL 1979), significant asymmetry between left and right ICA origins were found.

level of bifurcation
- left higher 50%
- right higher 22%
- same height 28%
orientation of origin
- dorsolateral or dorsal aspect of CCA : right 82%, left 94%

Segments

There are several classification systems, the most recent of which was described by Bouthillier et al in Neurosurgery, 1996 (see below). Their classification system is used clinically by neurosurgeons, neuroradiologists and nuerologists and relies on the angiographic appearance of the vessel and histological comparison rather than on the embryonic development.

There are 7 segments in the Bouthillier classification:

cervical segment
petrous segment
lacerum segment
cavernous segment
clinoid segment
ophthalmic (supraclinoid) segment
communicating (terminal) segment

Branches

Except for the terminal segment (C7) the odd numbered segments usually have no branches, whereas the even numbered segments (C2, C4, C6) each have two branches.