| Internal carotid artery | |
|---|---|
 | |
 Arteries of the neck. The internal carotid arteries arise from thecommon carotid arteries - labeledCommon caroti on the figure. | |
| Details | |
| Precursor | 3.Aortic arch |
| Source | Common carotid artery |
| Branches | Ophthalmic,anterior choroidal,anterior cerebral,middle cerebral andposterior communicating artery |
| Vein | Internal jugular vein |
| Identifiers | |
| Latin | arteria carotis interna |
| MeSH | D002343 |
| TA98 | A12.2.06.001 |
| TA2 | 4463 |
| FMA | 3947 |
| Anatomical terminology | |
Theinternal carotid artery is anartery in theneck which supplies theanterior andmiddlecerebral circulation.[1]
In human anatomy, the internal andexternal carotid arise from thecommon carotid artery, where it bifurcates atcervical vertebrae C3 or C4. The internal carotid artery supplies thebrain, including the eyes,[2] while the external carotid nourishes other portions of the head, such as theface,scalp,skull, andmeninges.
Terminologia Anatomica in 1998 subdivided the artery into four parts: "cervical", "petrous", "cavernous", and "cerebral".[3][4]
In clinical settings, however, usually the classification system of the internal carotid artery follows the 1996 recommendations by Bouthillier,[5] describing seven anatomical segments of the internal carotid artery, each with a corresponding alphanumeric identifier: C1 cervical; C2 petrous; C3 lacerum; C4 cavernous; C5 clinoid; C6 ophthalmic; and C7 communicating. The Bouthillier nomenclature remains in widespread use by neurosurgeons, neuroradiologists and neurologists.
The segments are subdivided based on anatomical and microsurgical landmarks and surrounding anatomy, more thanangiographic appearance of the artery. An alternativeembryologic classification system proposed byPierre Lasjaunias[6] and colleagues is invaluable when it comes to explanation of many internal carotid artery variants. An older clinical classification, based on pioneering work by Fischer,[7] is mainly of historical significance.
The segments of the internal carotid artery are as follows:
The internal carotid artery is a terminal branch of thecommon carotid artery; it arises around the level of the fourth cervicalvertebra when the common carotid bifurcates into this artery and its more superficial counterpart, theexternal carotid artery.
Thecervical segment, or C1, orcervical part of the internal carotid, extends from the carotid bifurcation until it enters thecarotid canal in the skull anterior to thejugular foramen.
At its origin, the internal carotid artery is somewhat dilated. This part of the artery is known as thecarotid sinus or the carotid bulb. The ascending portion of the cervical segment occurs distal to the bulb when the vessel walls are again parallel.
The internal carotid runs vertically upward in thecarotid sheath and enters theskull through thecarotid canal. During this part of its course, it lies in front of thetransverse processes of the upper three cervical vertebrae.
It is relatively superficial at its start, where it is contained in thecarotid triangle of the neck, and lies behind and medial to the external carotid, overlapped by thesternocleidomastoid muscle, and covered by the deep fascia, theplatysma, and integument: it then passes beneath theparotid gland, being crossed by thehypoglossal nerve, thedigastric muscle and thestylohyoid muscle, theoccipital artery and theposterior auricular artery. Higher up, it is separated from the external carotid by thestyloglossus andstylopharyngeus muscles, the tip of thestyloid process and thestylohyoid ligament, theglossopharyngeal nerve and the pharyngeal branch of thevagus nerve. It is in relation, behind, with thelongus capitis, thesuperior cervical ganglion of thesympathetic trunk, and thesuperior laryngeal nerve; laterally, with theinternal jugular vein andvagus nerve, the nerve lying on a plane posterior to the artery; medially, with thepharynx,superior laryngeal nerve, andascending pharyngeal artery. At the base of the skull theglossopharyngeal, vagus,accessory, andhypoglossal nerves lie between the artery and theinternal jugular vein.
Unlike theexternal carotid artery, the internal carotid normally has no branches in theneck.
Thepetrous segment, or C2, of the internal carotid, is that which is inside the petrous part of thetemporal bone. This segment extends until theforamen lacerum.
The petrous portion classically has three sections:
When the internal carotid artery enters the canal in thepetrous portion of the temporal bone, it first ascends a short distance and then curves anteriorly and medially. The artery lies at first in front of thecochlea andtympanic cavity; from the latter cavity it is separated by a thin, bony lamella, which is cribriform in the young subject, and often partly absorbed in old age. Farther forward, it is separated from thetrigeminal ganglion by a thin plate of bone, which forms the floor of the fossa for the ganglion and the roof of the horizontal portion of the canal. Frequently this bony plate is more or less deficient, and then the ganglion is separated from the artery by fibrous membrane. The artery is separated from the bony wall of thecarotid canal by a prolongation ofdura mater and is surrounded by a number of small veins and by filaments of thecarotid plexus, derived from the ascending branch of thesuperior cervical ganglion of the sympathetic trunk.
The named branches of the petrous segment of the internal carotid artery are:
Thelacerum segment, or C3, is a short segment that begins above theforamen lacerum and ends at thepetrolingual ligament, a reflection ofperiosteum between the lingula and petrous apex (or petrosal process) of thesphenoid bone. The lacerum portion is still considered "extradural" since it is surrounded by periosteum and fibrocartilage along its course. It is erroneously stated in several anatomy textbooks that the internal carotid artery passes through the foramen lacerum. This at best has only ever been a partial truth in that it passes through the superior part of the foramen on its way to the cavernous sinus. As such it does not traverse the skull through it. The inferior part of the foramen is actually filled with fibrocartilage. The broad consensus is that the internal carotid artery should not be described as travelling through the foramen lacerum.[8]
Thecavernous segment, or C4, of the internal carotid artery begins at the petrolingual ligament and extends to the proximal dural ring, which is formed by the medial and inferior periosteum of the anterior clinoid process. The cavernous segment is surrounded by thecavernous sinus.
In this part of its course, the artery is situated between the layers of thedura mater forming thecavernous sinus, but covered by the lining membrane of the sinus. It at first ascends toward theposterior clinoid process, then passes forward by the side of thebody of the sphenoid bone, again curves upward on the medial side of theanterior clinoid process, and perforates the dura mater forming the roof of the sinus. The curve in the cavernous segment is called thecarotid siphon. This portion of the artery is surrounded by filaments of the sympathetic trunk, and on its lateral side is theabducent nerve, or cranial nerve VI.
The named branches of the cavernous segment are:
The cavernous segment also gives rise to small capsular arteries that supply the wall of the cavernous sinus.
Theclinoid segment, or C5, is another short segment of the internal carotid that begins after the artery exits thecavernous sinus at the proximal dural ring and extends distally to the distal dural ring, after which the carotid artery is considered "intra-dural" and has entered thesubarachnoid space.
The clinoid segment normally has no named branches, though theophthalmic artery may arise from the clinoid segment.
Theophthalmic segment, or C6, extends from the distal dural ring, which is continuous with the falx cerebri, to the origin of theposterior communicating artery. The ophthalmic segment courses roughly horizontally, parallel to theoptic nerve, which runs superomedially to the carotid at this point.
The named branches of the ophthalmic segment are:
Thecommunicating segment, or terminal segment, or C7, of the internal carotid artery passes between the optic and oculomotor nerves to the anterior perforated substance at the medial extremity of the lateral cerebral fissure. Angiographically, this segment extends from the origin of theposterior communicating artery to the bifurcation of the internal carotid artery.
The named branches of the communicating segment are:
The internal carotid then divides to form theanterior cerebral artery andmiddle cerebral artery. Thecircle of Willis provides acollateral pathway for blood supply to the brain.
The following are the branches of the internal carotid artery, listed by segment:[9]
Thesympathetic trunk forms a plexus of nerves around the artery known as thecarotid plexus. Theinternal carotid nerve arises from thesuperior cervical ganglion, and forms this plexus, which follows the internal carotid into the skull.
The state and health of internal carotid arteries is usually evaluated usingdoppler ultrasound,CT angiogram orphase contrast magnetic resonance imaging (PC-MRI).
Typically internal carotid artery blood flow velocities are measured in peak systolic velocity (PSV) and end diastolic velocity (EDV) and according to Society of Radiologists in Ultrasound in healthy subjects without stenosis must be below 125 cm/sec at PSV and below 40 cm/sec at EDV.[10]
One study found that fornormative males in the 20-39 age group, PSV averaged 82 cm/sec and EDV 34 cm/sec. In the male 80+ age group, PSV averaged 76 cm/sec and EDV 18 cm/sec.[11]
This article incorporates text in thepublic domain frompage 566 of the 20th edition ofGray's Anatomy(1918)
The arterial input to the eye is provided by several branches from the ophthalmic artery, which is derived from the internal carotid artery in most mammals.
