Internal Carotid Artery
The internal carotid artery is one of the two arterial branches that stems from the common carotid artery. The carotid artery arises both directly and indirectly from the arch of the aorta, depending on which side of the body it belongs to. The right common carotid artery arises indirectly, because it bifurcates from the first aortic branch which is the brachiocephalic artery, along with the right subclavian artery. The left common carotid artery arises as the second aortic branch, with the left subclavian artery also originating directly from the aorta just to the left.
There are two main ways to categorize the areas of the internal carotid artery. In 1998 the international ‘Terminologia Anatomica’ announced that there are four segments to the artery, including the cervical segment, the petrous segment, the cavernous segment and the cerebral segment. Earlier in 1996 however Bouthillier put forward a more complex idea that the internal carotid had no less than seven segments. The latter idea is generally accepted clinically.
Bouthilier's segments are organized by the letter ‘C’ and its corresponding number ranging from one to seven which gives the segments an order.
- C1 - Cervical segment
- C2 - Petrous segment
- C3 - Lacerum segment
- C4 - Cavernous segment
- C5 - Clinoid segment
- C6 - Ophthalmic segment
- C7 - Communicating segment
Because this article has previously discussed the categorization of the internal carotid artery into segments, the branches of this artery will now be mentioned by segment, so that the reader will gain insight to the theoretical borders of each segment. The cervical segment (C1), the lacerum segment (C3) and the clinoid Segment (C5) don’t have any arterial branches. The petrous segment (C2) gives the caroticotympanic arteries and the vidian artery. The cavernous segment (C4) gives rise to branches that stem from the meningohypophyseal trunk that include the tentorial basal branch, the tentorial marginal branch, the meningeal branch, the clivus branches and the inferior hypophyseal artery. The capsular branches also come from the fourth segment as do the branches from the inferolateral trunk, namely the branches that supply the trigeminal ganglion, the artery of the foramen rotundum and branches that run with certain nerves. The ophthalmic segment (C6) contains the ophthalmic artery and the superior hypophyseal artery. Finally, the communicating portion (C7) contains the posterior communicating artery, the anterior choroidal artery and the anterior and middle cerebral artery.
Stenosis of the carotid arteries, which include both the common carotid as well as the internal and external branches, is most commonly caused by a pathological disorder known as arteriosclerosis. This is a general term that is used to categorize arterial disorders which cause rigidity and thickening of the blood vessels. Fibrous plaques occur on the inner arterial walls which are composed of hyaline and are dangerous due to the fact that in a complicated case, hemorrhage, ulceration, calcification, thrombus formation and embolization can occur. In a case like this, medication is simply not enough, but an alteration of diet and lifestyle can help arrest but also completely prevent such a disease.