These large arteries are the left and right branches of the common carotid artery in the neck which enter the skull, as opposed to the external carotid artery branches which supply the facial tissues.
The internal carotid artery branches into the anterior cerebral artery and continues to form the middle cerebral artery.
The internal carotid artery is major paired artery, one on each side of the head and neck, in human anatomy. They arise from the common carotid artery where these bifurcate into the internal and external carotid artery; the internal carotid artery supplies the brain, while the external carotid nourishes other portions of the head, such as face, scalp, skull, and meninges.
The internal carotid arteries supply blood to the anterior three-fifths of cerebrum, except for parts of the temporal and occipital lobes.
Any decrease in the flow of blood through one of the internal carotid arteries brings about some impairment in the function of the frontal lobes. This impairment may result in numbness, weakness, or paralysis on the side of the body opposite to the obstruction of the artery.
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 artery or arteries
Artery of pterygoid canal (vidian artery)
C3: Branches from the lacerum portion - none
Superior hypophyseal artery
C7: Branches from the communicating portion
Posterior communicating artery
Anterior choroidal artery
Anterior cerebral artery (a terminal branch)
Middle cerebral artery (a terminal branch)
The microsurgical anatomy of the supraclinoid portion of the internal carotid artery (ICA) was studied in 50 adult cadaver cerebral hemispheres using X 3 to X 40 magnification.
The ICA was divided into four parts:
The C1 or cervical portion
The C2 or petrous portion
The C3 or cavernous portion
The C4 or supraclinoid portion.
C5 or clinoid portion
C6 ophthalmic portion
C7: Communicating portion
see also Carotid Siphon
AC: anterior clinoid process; ICA: internal carotid artery; LT: lamina terminalis; ON: optic nerve; OlN; olfactory nerve; SW: sphenoid wing; TS: tuberculum sellae; A1: A1 segment of the Anterior Cerebral Artery; A2: A2 segment of the Anterior Cerebral Artery; M1: M1 segment of the Middle Cerebral Artery
The clinoid segment of the internal carotid artery (ICA) is the portion that abuts the clinoid process. This portion of the ICA can be directly observed only after removal of the clinoid process. The dura of the cavernous sinus roof separates to enclose the clinoid process. The clinoid segment of the ICA exists only where this separation of dural layers is present. Because the clinoid process does not completely enclose the ICA in most cases, the clinoid segment is shaped more like a wedge than a cylinder. The outer layer of the dura (dura propria) is a thick membrane that fuses with the adventitia of the ICA to form a competent ring that separates the intradural ICA from the extradural ICA. The thin inner membranous layer of the dura loosely surrounds the ICA throughout the entire length of its clinoid segment. The most proximal aspect of this membrane defines the proximal dural ring. The proximal ring is incompetent and admits a variable number of veins from the cavernous plexus that accompany the ICA throughout its clinoid segment.
The narrow space between the inner dural layer and the clinoid ICA is continuous with the cavernous sinus via an incompetent proximal dural ring. This space between the clinoid ICA and the inner dural layer contains a variable number of veins that directly communicate with the cavernous plexus. Given the inconstancy of the venous plexus surrounding the clinoid ICA, we think that categorical labeling of the clinoid ICA as intracavernous or extracavernous cannot be justified 2).
The C4 portion was divided into three segments based on the origin of its major branches: the ophthalmic segment extended from the origin of the ophthalmic artery to the origin of the posterior communicating artery (PCoA); the communicating segment extended from the origin of the PCoA to the origin of the anterior choroidal artery (AChA); and the choroidal segment extended from the origin of the AChA to the bifurcation of the carotid artery. Each segment gave off a series of perforating branches with a relatively constant site of termination. The perforating branches arising from the ophthalmic segment passed to the optic nerve and chiasm, infundibulum, and the floor of the third ventricle. The perforating branches arising from the communicating segment passed to the optic tract and the floor of the third ventricle. The perforating branches arises from the choroidal segment passed upward and entered the brain through the anterior perforated substance. The anatomy of the ophthalmic, posterior communicating, anterior choroidal, and superior hypophyseal branches of the C4 portion was also examined 3).
Based on anatomic correlations, the ICA may be described as 6 distinct segments:
(2) petrous (carotid canal to posterolateral aspect of foramen lacerum)
(4) parasellar (superomedial petrous apex to the proximal dural ring)
(5) paraclinoid (from the proximal to the distal dural rings)
(6) intradural (distal ring to ICA bifurcation).
Corresponding surgical landmarks included the Eustachian tube, the fossa of Rosenmüller, and levator veli palatini for the parapharyngeal segment; the vidian canal and V3 for the petrous segment; the fibrocartilage of foramen lacerum, foramen rotundum, maxillary strut, lingular process of the sphenoid bone, and paraclival protuberance for the paraclival segment; the sellar floor and petrous apex for the parasellar segment; and the medial and lateral opticocarotid and lateral tubercular recesses, as well as the distal osseous arch of the carotid sulcus for the paraclinoid segment 4).