Arteries to Brain and Meninges


Internal Carotid Artery


The internal carotid arteries (ICAs) ascend vertically in the neck, posterior and slightly medial to the external carotid artery. These arteries are positioned medial to the sternocleidomastoid muscle and travel behind the faucial pillars of the pharynx until they reach the carotid canal at the skull base. They have no branches within the neck. At the skull base, the carotid arteries lie adjacent to the 9th to 12th cranial nerves, which exit the skull from the jugular and hypoglossal foramina. The arteries then enter the skull through the carotid canal within the petrous bone and form an S-shaped curve. The portion of the internal carotid arteries within this curve is referred to as the carotid siphon. There are three divisions of the internal carotid arteries within the siphon: an intrapetrous portion, an intracavernous portion within the cavernous sinus, and a supraclinoidal portion.


Branches. Two branches arise from the petrous segment: the caroticotympanic artery supplying the tympanic cavity and the artery of the pterygoid canal (vidian artery) supplying the pharynx and the tympanic cavity. The cavernous segment gives off the meningohypophyseal trunk supplying branches to the pituitary gland and meninges and the anterior meningeal artery. Within the cavernous sinus, the internal carotid artery lies in close relationship to the nerves that control eye movement (III, IV, and VI) and the ophthalmic and maxillary divisions of V. Soon after leaving the cavernous sinus, medial to the anterior clinoid process, the internal carotid artery gives off the ophthalmic artery. The ophthalmic artery passes through the optic canal into the orbit just below and lateral to the optic nerve.


The internal carotid arteries penetrate the dura mater, forming the supraclinoid segment. They ascend slightly posteriorly and laterally, passing between the oculomotor and optic nerves. The branches of the proximal supraclinoid region are the anterior choroidal, superior hypophyseal, and posterior communicating arteries, which arise and course posteriorly. The termination of the intracranial internal carotid arteries (the so-called T portion because of its shape) is the bifurcation into the anterior cerebral arteries, which course medially, and the middle cerebral arteries, which course laterally.


Vertebral Artery Extracranial


Segments. The first branch of each subclavian artery is the vertebral artery (VA). The thyrocervical and costocervical trunks originate from the subclavian arteries just after the vertebral artery and can serve as collateral channels when the vertebral artery becomes occluded. The vertebral arteries course upward and backward during their first segment (V1) until they enter the transverse foramina of the sixth or fifth cervical vertebra. Then the artery ascends as the second segment (V2), which courses within the intravertebral foramina, exiting from the transverse process of the atlas. The third segment (V3) passes posteriorly behind the articular process of the atlas; it lies in a groove on the upper surface of the posterior arch of the atlas, behind the atlas, before piercing the dura mater to enter the foramen magnum. The intracranial portion (V4) ends at the medullopontine junction, where the two VAs join to form the basilar artery.


Branches. The cervical portion of the vertebral arteries gives rise to many muscular and spinal radicular branches. The spinal branches pass through the intervertebral foramina and enter the spinal canal to supply the cervical portion of the spinal cord and the periosteum and bodies of the cervical vertebra. A small anterior and larger posterior meningeal artery originate from the distal extracranial segments (V2, V3). The intracranial vertebral arteries give off posterior and anterior spinal artery branches, penetrating arteries to the medulla, and the large posterior inferior cerebellar arteries.


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Sep 2, 2016 | Posted by in NEUROLOGY | Comments Off on Arteries to Brain and Meninges

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