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The internal carotid artery (Latin: arteria carotis interna) is an artery in the neck which supplies the anterior circulation of the brain. In human anatomy, the internal and external carotids arise from the common carotid arteries, where these bifurcate at
cervical vertebrae In tetrapods, cervical vertebrae (singular: vertebra) are the vertebrae of the neck, immediately below the skull. Truncal vertebrae (divided into thoracic and lumbar vertebrae in mammals) lie caudal (toward the tail) of cervical vertebrae. In ...
C3 or C4. The internal carotid artery supplies the brain, including the eyes, while the external carotid nourishes other portions of the head, such as the face, scalp,
skull The skull is a bone protective cavity for the brain. The skull is composed of four types of bone i.e., cranial bones, facial bones, ear ossicles and hyoid bone. However two parts are more prominent: the cranium and the mandible. In humans, th ...
, and meninges.


Classification

Terminologia Anatomica in 1998 subdivided the artery into four parts: "cervical", "petrous", "cavernous", and "cerebral". However, in clinical settings, the classification system of the internal carotid artery usually follows the 1996 recommendations by Bouthillier, 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 than
angiographic Angiography or arteriography is a medical imaging technique used to visualize the inside, or lumen, of blood vessels and organs of the body, with particular interest in the arteries, veins, and the heart chambers. Modern angiography is perform ...
appearance of the artery. An alternative embryologic classification system proposed by Pierre Lasjaunias 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, is mainly of historical significance. The segments of the internal carotid artery are as follows: * Cervical segment, or C1, identical to the commonly used cervical portion * Petrous segment, or C2 * Lacerum segment, or C3 **C2 and C3 compose the commonly termed petrous portion * Cavernous segment, or C4, almost identical to the commonly used cavernous portion * Clinoid segment, or C5. This segment is not identified in some earlier classifications and lies between the commonly used cavernous portion and cerebral or supraclinoid portion. * Ophthalmic, or supraclinoid segment, or C6 * Communicating, or terminal segment, or C7 ** C6 and C7 together constitute the commonly used cerebral or supraclinoid portion.


Course/Part

The internal carotid artery is a terminal branch of the common carotid artery; it arises around the level of the fourth cervical vertebra when the common carotid bifurcates into this artery and its more superficial counterpart, the external carotid artery.


C1: Cervical segment

The cervical segment, or C1, or cervical part of the internal carotid, extends from the carotid bifurcation until it enters the
carotid canal The carotid canal is a passageway in the temporal bone of the skull through which the internal carotid artery enters the middle cranial fossa from the neck. Structure The carotid canal is located within the middle cranial fossa, at the petrous ...
in the skull anterior to the jugular foramen. At its origin, the internal carotid artery is somewhat dilated. This part of the artery is known as the carotid 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 the
carotid sheath The carotid sheath is an anatomical term for the fibrous connective tissue that surrounds the vascular compartment of the neck. It is part of the deep cervical fascia of the neck, below the superficial cervical fascia meaning the subcutaneous adi ...
and enters the
skull The skull is a bone protective cavity for the brain. The skull is composed of four types of bone i.e., cranial bones, facial bones, ear ossicles and hyoid bone. However two parts are more prominent: the cranium and the mandible. In humans, th ...
through the
carotid canal The carotid canal is a passageway in the temporal bone of the skull through which the internal carotid artery enters the middle cranial fossa from the neck. Structure The carotid canal is located within the middle cranial fossa, at the petrous ...
. During this part of its course, it lies in front of the transverse processes of the upper three cervical vertebrae. It is relatively superficial at its start, where it is contained in the carotid triangle of the neck, and lies behind and medial to the external carotid, overlapped by the sternocleidomastoid muscle, and covered by the deep fascia, the platysma, and integument: it then passes beneath the parotid gland, being crossed by the
hypoglossal nerve The hypoglossal nerve, also known as the twelfth cranial nerve, cranial nerve XII, or simply CN XII, is a cranial nerve that innervates all the extrinsic and intrinsic muscles of the tongue except for the palatoglossus, which is innervated ...
, the
digastric muscle The digastric muscle (also digastricus) (named ''digastric'' as it has two 'bellies') is a small muscle located under the jaw. The term "digastric muscle" refers to this specific muscle. However, other muscles that have two separate muscle bell ...
and the stylohyoid muscle, the
occipital artery The occipital artery arises from the external carotid artery opposite the facial artery. Its path is below the posterior belly of digastric to the occipital region. This artery supplies blood to the back of the scalp and sternocleidomastoid musc ...
and the posterior auricular artery. Higher up, it is separated from the external carotid by the styloglossus and stylopharyngeus muscles, the tip of the styloid process and the
stylohyoid ligament The stylohyoid ligament is a ligament that connects the hyoid bone to the temporal styloid process (of the temporal bone of the skull). Structure The stylohyoid ligament connects the lesser horn of hyoid bone to the styloid process of the t ...
, the
glossopharyngeal nerve The glossopharyngeal nerve (), also known as the ninth cranial nerve, cranial nerve IX, or simply CN IX, is a cranial nerve that exits the brainstem from the sides of the upper medulla, just anterior (closer to the nose) to the vagus nerve. ...
and the pharyngeal branch of the
vagus nerve The vagus nerve, also known as the tenth cranial nerve, cranial nerve X, or simply CN X, is a cranial nerve that interfaces with the parasympathetic control of the heart, lungs, and digestive tract. It comprises two nerves—the left and righ ...
. It is in relation, behind, with the longus capitis, the superior cervical ganglion of the sympathetic trunk, and the superior laryngeal nerve; laterally, with the internal jugular vein and vagus nerve, the nerve lying on a plane posterior to the artery; medially, with the
pharynx The pharynx (plural: pharynges) is the part of the throat behind the mouth and nasal cavity, and above the oesophagus and trachea (the tubes going down to the stomach and the lungs). It is found in vertebrates and invertebrates, though its st ...
, superior laryngeal nerve, and ascending pharyngeal artery. At the base of the skull the glossopharyngeal, vagus, accessory, and hypoglossal nerves lie between the artery and the internal jugular vein. Unlike the external carotid artery, the internal carotid normally has no branches in the neck.


C2: Petrous segment

The petrous segment, or C2, of the internal carotid, is that which is inside the petrous part of the temporal bone. This segment extends until the foramen lacerum. The petrous portion classically has three sections: an ascending, or vertical, portion; the genu, or bend; and the horizontal portion. When the internal carotid artery enters the canal in the petrous 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 the
cochlea The cochlea is the part of the inner ear involved in hearing. It is a spiral-shaped cavity in the bony labyrinth, in humans making 2.75 turns around its axis, the modiolus. A core component of the cochlea is the Organ of Corti, the sensory o ...
and
tympanic cavity The tympanic cavity is a small cavity surrounding the bones of the middle ear. Within it sit the ossicles, three small bones that transmit vibrations used in the detection of sound. Structure On its lateral surface, it abuts the external auditor ...
; 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 the
trigeminal ganglion A trigeminal ganglion (or Gasserian ganglion, or semilunar ganglion, or Gasser's ganglion) is the sensory ganglion at the base of each of the two trigeminal nerves (CN V), occupying a cavity ( Meckel's cave) in the dura mater, covering the tri ...
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 the
carotid canal The carotid canal is a passageway in the temporal bone of the skull through which the internal carotid artery enters the middle cranial fossa from the neck. Structure The carotid canal is located within the middle cranial fossa, at the petrous ...
by a prolongation of dura mater and is surrounded by a number of small veins and by filaments of the carotid plexus, derived from the ascending branch of the superior cervical ganglion of the sympathetic trunk. The named branches of the petrous segment of the internal carotid artery are: *the
vidian artery The artery of the pterygoid canal (or Vidian artery) is an artery in the pterygoid canal, in the head. It usually arises from the external carotid artery, but can arise from either the internal or external carotid artery or serve as an anastomosis ...
or artery of the pterygoid canal *the caroticotympanic artery


C3: Lacerum segment

The lacerum segment, or C3, is a short segment that begins above the foramen lacerum and ends at the petrolingual ligament, a reflection of periosteum between the lingula and petrous apex (or petrosal process) of the sphenoid 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.TAUBER M, VAN LOVEREN H. R et al. The enigmatic foramen lacerum. Commentaries. Neurosurgery. 1999, vol. 44, no2, pp. 386-39

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C4: Cavernous segment

The cavernous 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 the cavernous sinus. In this part of its course, the artery is situated between the layers of the dura mater forming the cavernous sinus, but covered by the lining membrane of the sinus. It at first ascends toward the posterior clinoid process, then passes forward by the side of the body of the sphenoid bone, again curves upward on the medial side of the
anterior clinoid process In the sphenoid bone, the posterior border, smooth and rounded, is received into the lateral fissure of the brain; the medial end of this border forms the anterior clinoid process, which gives attachment to the tentorium cerebelli; it is sometimes ...
, and perforates the dura mater forming the roof of the sinus. The curve in the cavernous segment is called the carotid siphon. This portion of the artery is surrounded by filaments of the sympathetic trunk, and on its lateral side is the
abducent nerve The abducens nerve or abducent nerve, also known as the sixth cranial nerve, cranial nerve VI, or simply CN VI, is a cranial nerve in humans and various other animals that controls the movement of the lateral rectus muscle, one of the extraocula ...
, or cranial nerve VI. The named branches of the cavernous segment are: * the meningohypophyseal artery * the inferolateral trunk The cavernous segment also gives rise to small capsular arteries that supply the wall of the cavernous sinus.


C5: Clinoid segment

The clinoid segment, or C5, is another short segment of the internal carotid that begins after the artery exits the cavernous 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 the subarachnoid space. The clinoid segment normally has no named branches, though the ophthalmic artery may arise from the clinoid segment.


C6: Ophthalmic segment

The ophthalmic segment, or C6, extends from the distal dural ring, which is continuous with the falx cerebri, to the origin of the
posterior communicating artery In human anatomy, the left and right posterior communicating arteries are arteries at the base of the brain that form part of the circle of Willis. Each posterior communicating artery connects the three cerebral arteries of the same side. Anterio ...
. The ophthalmic segment courses roughly horizontally, parallel to the
optic nerve In neuroanatomy, the optic nerve, also known as the second cranial nerve, cranial nerve II, or simply CN II, is a paired cranial nerve that transmits visual information from the retina to the brain. In humans, the optic nerve is derived fro ...
, which runs superomedially to the carotid at this point. The named branches of the ophthalmic segment are: *the ophthalmic artery *the superior hypophyseal artery


C7: Communicating segment

The communicating 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 the
posterior communicating artery In human anatomy, the left and right posterior communicating arteries are arteries at the base of the brain that form part of the circle of Willis. Each posterior communicating artery connects the three cerebral arteries of the same side. Anterio ...
to the bifurcation of the internal carotid artery. The named branches of the communicating segment are: *the
posterior communicating artery In human anatomy, the left and right posterior communicating arteries are arteries at the base of the brain that form part of the circle of Willis. Each posterior communicating artery connects the three cerebral arteries of the same side. Anterio ...
*the anterior choroidal artery The internal carotid then divides to form the
anterior cerebral artery The anterior cerebral artery (ACA) is one of a pair of cerebral arteries that supplies oxygenated blood to most midline portions of the frontal lobes and superior medial parietal lobes of the brain. The two anterior cerebral arteries arise from ...
and middle cerebral artery. The
Circle of Willis The circle of Willis (also called Willis' circle, loop of Willis, cerebral arterial circle, and Willis polygon) is a circulatory anastomosis that supplies blood to the brain and surrounding structures in reptiles, birds and mammals, including hu ...
provides a collateral pathway for blood supply to the brain.


Branches

The following are the branches of the internal carotid artery, listed by segment: * C1: Branches from the cervical portion - none * C2: Branches from the petrous portion ** Caroticotympanic arteries ** Artery of pterygoid canal (vidian artery) * C3: Branches from the lacerum portion - none * C4: Branches from the cavernous portion **Branches of the meningohypophyseal trunk: *** Tentorial basal branch *** Tentorial marginal branch *** Meningeal branch - helps supply blood to the meninges of the anterior cranial fossa *** Clivus branches - tiny branches that supply the clivus *** Inferior hypophyseal artery ** Capsular branches - supplies wall of cavernous sinus ** Branches of the inferolateral trunk: *** Branches to trigeminal ganglion - provide blood to
trigeminal ganglion A trigeminal ganglion (or Gasserian ganglion, or semilunar ganglion, or Gasser's ganglion) is the sensory ganglion at the base of each of the two trigeminal nerves (CN V), occupying a cavity ( Meckel's cave) in the dura mater, covering the tri ...
*** ''Artery of the foramen rotundum'' *** Branches to nerves * C5: Branches from the clinoid portion - none * C6: Branches from the ophthalmic portion ** Ophthalmic artery ** Superior hypophyseal artery * C7: Branches from the communicating portion **
Posterior communicating artery In human anatomy, the left and right posterior communicating arteries are arteries at the base of the brain that form part of the circle of Willis. Each posterior communicating artery connects the three cerebral arteries of the same side. Anterio ...
** Anterior choroidal artery **
Anterior cerebral artery The anterior cerebral artery (ACA) is one of a pair of cerebral arteries that supplies oxygenated blood to most midline portions of the frontal lobes and superior medial parietal lobes of the brain. The two anterior cerebral arteries arise from ...
(a terminal branch) ** Middle cerebral artery (a terminal branch)


Carotid plexus

The sympathetic trunk forms a plexus of nerves around the artery known as the carotid plexus. The internal carotid nerve arises from the superior cervical ganglion, and forms this plexus, which follows the internal carotid into the skull.


Additional images

File:Circle of willis.png, Circle of Willis File:Circle of Willis en.svg , Diagram of the arterial circulation at the base of the brain (inferior view).


See also

* Carotid endarterectomy * Carotid body


References


External links

* *
The Anatomy Wiz.
Internal Carotid Artery
Aneurysms of the Internal Carotid Artery
{{Authority control Arteries of the head and neck