Anatomy clinical correlates: Anterior blood supply to the brain

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Anatomy clinical correlates: Anterior blood supply to the brain

USMLE® Step 1 questions

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A 70-year-old man is brought to the emergency department for evaluation of headache, nausea, and vomiting for the past 24 hours. His partner states he has been more irritable and has had trouble remembering to do routine errands. Two weeks ago, the patient fell while skiing but did not seek medical evaluation. Past medical history is significant for coronary artery disease and hypertension. Current medications include atenolol, enalapril, furosemide, atorvastatin, and aspirin. The patient has smoked a pack of cigarettes daily for 40 years. Temperature is 37°C (98.6°F), pulse is 99/min, respirations are 16/min, and blood pressure is 160/90 mm Hg. The patient is ill-appearing. He is oriented to person, but not to place or time. During the examination, the patient is unable to answer questions or follow commands. Deep tendon reflexes are 4+ on the right and 2+ on the left. Babinski sign is present on the right. There is 4/5 weakness of the right hip flexors. The patient’s non-contrast head CT is demonstrated below.

Reproduced from Radiopedia

Disruption of which of the following structures is the most likely cause of this patient’s symptoms? 


Your brain is awake and working hard all day, every day, even when you’re sleeping! So it makes sense that it needs a lot of oxygen and energy, which is why it is well supplied from several major arteries. The circulation of the brain can ultimately be divided into the anterior and posterior circulation, and understanding their anatomy can help us understand the clinical consequences and management of various issues that can arise! So let’s delve into the anterior circulation of the brain!

Remember that the anterior circulation supplies the anterior portion of the brain, and comes from the internal carotid arteries which divide into the anterior and middle cerebral arteries. The anterior circulation then connects to the posterior circulation through the posterior communicating arteries. The posterior circulation comes from the vertebral arteries, which combine to form the basilar artery. Together, the connection between the anterior and posterior circulation form the circle of Willis, which is an anastomotic network of arteries at the base of the brain which ensure adequate blood flow to the brain, even in cases where part of this circulation becomes occluded! However, there are still instances where obstruction of these arteries and their branches disrupts blood flow to the brain, causing a stroke, which can lead to irreversible neuronal damage.

Now, a stroke can be classified as either ischemic or hemorrhagic. Ischemic strokes are much more common, and they happen because of an acute blockage of one of the blood vessels supplying the brain. Ischemic strokes can be thrombotic, embolic or hypoxic. A thrombotic stroke occurs when there’s a blood clot in the artery, formed directly at the site of infarction, which typically occurs because of a ruptured atherosclerotic plaque. An embolic stroke, on the other hand, is where an embolus from another part of the body travels to the site of infarction to cause obstruction. For example, with atrial fibrillation, a blood clot can form in the heart, where it then travels through the circulation to eventually obstruct brain vessels. Then there are hypoxic strokes, where there is not a direct blockage of a vessel but systemic hypoperfusion or hypoxemia of the brain. This can cause inadequate oxygenation of the brain, especially in watershed areas which are supplied by the terminal branches of two large vessels, and are therefore more prone to hypoperfusion injuries. 


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