Territories of the Cerebral Arteries


The ECAs have two branches that supply the face and can provide collateral blood flow to the ICA system: the facial arteries, which course along the cheek toward the nasal bridge, where they are termed the angular arteries, and the preauricular arteries, which terminate as the superficial temporal arteries. The internal maxillary artery and ascending pharyngeal branches of the ECAs also can contribute to collateral circulation when an ICA occludes. The internal maxillary arteries give off the middle meningeal artery branches, which penetrate into the skull through the foramen spinosum. Another important arterial supply of the face involves the frontal and supratrochlear branches that originate from the ophthalmic arteries that supply the medial forehead above the brow. When an ICA occludes, these ECA branches can be important sources of collateral blood.


Anomalous Origins


The right common carotid artery and right subclavian arteries may arise as separate branches directly from the aortic arch. The right vertebral artery may arise directly from the brachiocephalic trunk instead of the right subclavian artery. The left vertebral artery may also arise from the brachiocephalic trunk. The right subclavian artery can arise from the aortic arch distal to the left subclavian artery, in which case it then crosses to the right side. Sometimes the left common carotid and the left subclavian arteries arise from a common (left brachiocephalic) trunk. Rarely, a VA can arise from a common carotid artery.


Supratentorial Arteries to the Brain


The internal carotid (anterior) circulation supplies the anterior and most of the lateral portions of the cerebral hemispheres, while the vertebrobasilar (posterior) circulation supplies the brainstem, cerebellum, and the posterior portion of the cerebral hemispheres. About 40% of the brain’s blood flow comes through each internal carotid artery, while 20% flows through the vertebrobasilar arterial system.


Circle of Willis


This anastomosis at the base of the brain (more a hexagon than a circle) serves to connect the major arteries of the anterior and posterior circulations, and the arteries from both sides. The horizontal portions of the anterior cerebral artery branches of the internal carotid arteries are connected to the anterior communicating artery, forming the anterior portion of the circle. The posterior communicating artery branches of the internal carotid arteries on each side connect to the posterior cerebral artery branches of the basilar artery, forming the lateral sides and posterior portion of the “circle.”


The superior hypophyseal arteries arise as the first branches of the supraclinoid portion of the internal carotid arteries, giving off branches to the optic chiasm and participating in an anastomosis that supplies the pituitary gland, which is composed of arterial branches from each side and branches of the right and left meningohypophyseal trunk.


The posterior communicating artery (about 1.5 cm in length) proceeds posteriorly and medially to join the posterior cerebral arteries on each side about 1 cm from their origins from the basilar artery. Small branches feed the optic tract and the posterior portion of the optic chiasm, the posterior hypothalamus, and the walls of the third ventricle. The tuberothalamic (polar) artery most often arises from the middle third of the posterior communicating artery but may also arise from the proximal segment of the posterior cerebral artery. The polar artery supplies the anteromedial and anterolateral portions of the thalamus.


Basilar Artery


The basilar artery is formed by the union of the two intracranial vertebral arteries at the medullo-pontine junction. It courses rostrally in a groove closely applied to the anterior surface of the pons, where it is located within the prepontine cistern behind the clivus. The distal segment enters the interpeduncular cistern, where it is often separated from the basal surface of the brainstem. The distal portion of the artery lies between the cerebral peduncles and ends at the pontomesencephalic junction, just after passing between the two oculomotor nerves, by dividing into the two posterior cerebral arteries. The basilar artery is often curved and tortuous and may deviate from the midline. The basilar artery averages about 33 cm in length, and the diameter usually is between 4 and 4.5 mm. The main branches of the artery are the anterior inferior and superior cerebellar arteries, paramedian arteries that penetrate directly into the pons, and short circumferential arteries that course around the pons and give off lateral basal and lateral tegmental penetrating arteries.


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Sep 2, 2016 | Posted by in NEUROLOGY | Comments Off on Territories of the Cerebral Arteries

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