Anatomy clinical correlates: Posterior blood supply to the brain

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A 67-year-old man comes to the office due to intermittent heaviness and paresthesias of the right arm. The patient has experienced multiple episodes over the past two months, especially while playing table tennis. Each episode is associated with nausea, dizziness, and visual disturbance. The patient has not had any falls or loss of consciousness. Past medical history includes hypertension, hyperlipidemia, and type 2 diabetes mellitus. Current medications include metformin, enalapril, and atorvastatin. The patient has smoked one pack of cigarettes for the past forty years and drinks alcohol occasionally. Orthostatic vitals are within normal limits. Physical examination demonstrates decreased radial and brachial pulses of the right upper extremity when compared to the left upper extremity. Skin over the right upper extremity feels cooler than the left. The remainder of the cardiopulmonary and neurologic exam are within normal limits. CT angiogram is performed and reveals a condition that results in reversal of blood flow through a vascular structure. Reverse blood flow through which of the following vessels is the most likely underlying etiology of this patient's symptoms?  

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Blood supply to the brain can be divided into an anterior and a posterior circulation. The posterior circulation supplies the cerebellum, brainstem, occipital lobes, and inferomedial temporal lobes, and comes from the vertebral arteries. The vertebral arteries combine to form the basilar artery, which eventually divides into the posterior cerebral arteries. The posterior circulation then connects to the anterior circulation through the posterior communicating arteries. Remember that the anterior circulation comes from the internal carotid artery which divides into the anterior and middle cerebral arteries. Together, the connection between the posterior and anterior circulation form the Circle of willis, which is an anastomotic network of arteries at the base of the brain that ensure adequate blood flow even in cases where part of this circulation becomes occluded! However, there are still instances where obstruction of these arteries and their branches can disrupt blood flow to the brain, so understanding their anatomy and what parts of the brain they nourish can help us better understand the clinical manifestations and management.

When blood flow to the brain is obstructed, that causes a stroke, which can be either ischemic or hemorrhagic. Ischemic strokes can be caused by thrombi, emboli, and hypoperfusion injuries, with the latter most commonly affecting the watershed areas of the brain. Hemorrhagic strokes, on the other hand, occur when there is a bleed within the brain tissue called an intracerebral or intraparenchymal hemorrhage, or a bleed in the subarachnoid space called a subarachnoid hemorrhage. The posterior circulation of the brain is susceptible to all of these, and the clinical signs and symptoms depend on which artery is occluded.

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