⭕️The #CircleofWillis is a vital arterial structure on the ventral surface of the brain that joins the two internal carotid arteries (ICAs) (two-thirds of the supply) with the two vertebral arteries to supply the contents of the cranium
⭕️The vertebral arteries enter the cranial cavity through the foramen magnum and join to become the basilar artery, which supplies blood to the posterior portion of the circle of Willis.
⭕️The internal carotid arteries enter the skull through the carotid canals and supply the anterior circulation of the brain.
⭕️After entering the skull, the ICA branches into two main vessels: the Anterior Cerebral Artery (ACA) and Middle Cerebral Artery (MCA).
⭕️The MCA supplies the lateral surface of the brain, traveling in the Sylvian fissure
⭕️The ACAs also originate from the ICA and run anterior and medially towards the midline, coursing over the corpus callosum, between the hemispheres in the longitudinal fissure, and supplying the medial aspect of the hemispheres as far back as the splenium. The anterior cerebral arteries are joined together by a single anterior communicating artery(ACom)
⭕️An ACA #stroke can result in paralysis or sensory loss of the legs, whereas a MCA stroke can result in loss of paralysis or sensory loss of the face and/or arms. A MCA stroke of the dominant hemisphere may injure the language centers and produce aphasia.
⭕️The two vertebral arteries lie on either side of the medulla and join anteriorly at the caudal border of the pons to form the basilar artery.
⭕️The vertebral arteries give off the posterior inferior cerebellar artery(PICA), before joining to form the basilar artery
⭕️Another important single artery that is created by the merger of the two vertebral arteries is the anterior spinal artery.
⭕️The basilar artery gives rise to a number of important paired branches. Posterior to anterior, these are: anterior inferior cerebellar artery(AICA), superior cerebellar artery(SCA).
⭕️The vertebral arteries supply the medulla via small, penetrating branches.
⭕️The basilar artery supplies the pons through small penetrating vessels.
⭕️PICA supply the inferior surface of the cerebellum, as well as the lateral medulla
⭕️AICA supplies the anterior portions of the cerebellum and the lateral pons.
⭕️SCAs supply the cerebellum and lateral midbrain
⭕️The basilar artery gives rise to the posterior cerebral arteries (PCAs), which join the anterior part of the circle of Willis via the posterior communicating arteries(PCom). PCAs supply the occipital lobe and lateral midbrain
⭕️The thalamus is supplied by perforators that originate from the tip of the basilar artery and the proximal PCA
⭕️Basilar artery strokes usually are fatal because they cause the loss of cardiac, respiratory, and reticular activating function. Patients who survive may have a clinical syndrome known as locked-in syndrome in which the patient cannot move as the ventral brainstem tracts (motor) are destroyed, but the sensory tracts (more dorsal) may be left intact. These patients are unable to move, speak, or communicate with the world, except by blinking and possibly through upgaze.
N.B.: VENOUS DRAINAGE
🔻The superior sagittal sinus lies along the attached edge of the falx cerebri, dividing the hemispheres, and usually drains into the right transverse sinus.
🔻The inferior sagittal sinus lies along the free edge of the falx and drains via the straight sinus into the left transverse sinus (The straight sinus lies in the tentorium cerebelli.)
🔻The transverse sinuses merge into the sigmoid sinuses before emerging from the cranium as the internal jugular veins.
🔻Deeper cranial structures drain via the two internal cerebral veins, which join to form the great cerebral vein (of Galen). This also drains into the inferior sagittal sinus.
🔻The cavernous sinuses lie on either side of the pituitary fossa and drain eventually into the transverse sinuses.
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