USMLE® Step 1 style questions USMLE
A 78-year-old right-handed man is brought to the emergency department following sudden-onset weakness in his right arm and inability to speak for twenty four hours. The patient’s daughter states she initially became concerned when he dropped his cup of coffee while walking to the kitchen table last night. The daughter states he has had a similar episode in the past that resolved spontaneously. He has a history of hypertension, for which he takes lisinopril. His temperature is 37°C (98.6°F), pulse is 92/min, and blood pressure is 158/104 mmHg. The patient is alert and visibly frustrated by not being able to speak. Physical examination reveals 2/5 strength in the right upper extremity and 4/5 strength in the right lower extremity. He follows written and verbal commands but is unable to speak or write. MRI of the head demonstrates ischemic changes in the cerebral territory supplied by the left middle cerebral artery. Which of the following histopathological findings are most likely to be observed in this patient’s brain at the present time?
Content Reviewers:Rishi Desai, MD, MPH
Contributors:Vincent Waldman, PhD
There are two main types of stroke: an ischemic stroke which is when there’s a blocked artery that reduces blood flow to the brain and a hemorrhagic stroke which is when an artery in the brain breaks, creating a pool of blood that damages the brain.
Now if symptoms self-resolve within 24 hours, it’s called a transient ischemic attack and there are usually minimal long-term problems.
OK - let’s start with some basic brain anatomy. The brain has a few regions - the most obvious is the cerebrum, which is divided into two cerebral hemispheres, each of which has a cortex - an outer region - divided into four lobes including the frontal lobe, parietal lobe, temporal lobe, and the occipital lobe.
The frontal lobe controls movement, and executive function, which is our ability to make decisions.
The parietal lobe processes sensory information, which lets us locate exactly where we are physically and guides movements in a three dimensional space.
Finally there’s the occipital lobe which is primarily responsible for vision.
The cerebellum helps with muscle coordination and balance.
Each of the internal carotid arteries also give off branches called the anterior cerebral arteries which serve the medial portion of the frontal and parietal lobes and connect with one another with a short little connecting blood vessel called the anterior communicating artery.
So together, the main arteries and the communicating arteries complete what is called the Circle of Willis - a ring where blood can circulate from one side to the other in case of a blockage.
The Circle of Willis offers alternative ways for blood to get around an obstructed vessel.
In general, the brain can get by on diminished blood flow - especially when it happens gradually because that allows enough time for collateral circulation to develop, which is where a nearby vessel starts sending out branches of blood vessels to serve an area that’s in need.
There are two main ways that an ischemic stroke happens.
One mechanism is endothelial cell dysfunction, which is when something irritates or inflames the slippery inner lining of the artery—the tunica intima.
One classic irritant is the toxins found in tobacco which float around in the blood damaging the endothelium.
That damage becomes a site for atherosclerosis, which is where a plaque forms. This is when a buildup of fat, cholesterol, proteins, calcium, and immune cells forms and starts to obstruct arterial blood flow.
This plaque has two parts to it, the soft cheesy-textured interior and the hard outer shell which is called the fibrous cap.
Usually, though, it takes years for plaque to build up, and this slow blockage only partially blocks the arteries, and so even though less blood makes it to brain tissue, there’s still some blood.
So strokes happen when there’s a sudden and complete or near-complete blockage of an artery—so let’s see how that can happen.
Since plaques sit in the lumen of the blood vessel, they’re constantly being stressed by mechanical forces from blood flow, and interestingly it’s often the smaller plaques that are more dangerous.
Their fibrous caps are softer than the larger ones and are prone to getting ripped off. Once that happens, the inner cheesy filling is exposed to the blood and is thrombogenic, which means that it tends to form clots very quickly.
Within a minute that artery can be fully blocked.
An embolic stroke typically happens when a blood clot breaks off from one location, travels through the blood, and gets lodged in an artery downstream, typically an artery, arteriole, or capillary with a smaller diameter. These blood clots typically emerge from atherosclerosis, but they can also form in the heart.
- "Robbins Basic Pathology" Elsevier (2017)
- "Harrison's Principles of Internal Medicine, Twentieth Edition (Vol.1 & Vol.2)" McGraw-Hill Education / Medical (2018)
- "Pathophysiology of Disease: An Introduction to Clinical Medicine 8E" McGraw-Hill Education / Medical (2018)
- "CURRENT Medical Diagnosis and Treatment 2020" McGraw-Hill Education / Medical (2019)
- "Stroke" The Lancet (2008)
- "Spontaneous intracerebral haemorrhage" BMJ (2009)