Medical School 2020, Year 1, Week 34

One of the first slides for the three hour-long lectures on higher cortical function involved an updated Gallz’s phrenology for 21st century tasks (https://blakerivers.files.wordpress.com/2010/06/male-female-brain.jpg). Tattooed Talia, sitting next to me, expressed outrage: “Shopping! Jealousy!” During a break, Pinterest Penelope, a female classmate and social chair whose laptop screen is often filled by Amazon or Pinterest during lecture, said to Talia, “I love your boots! Where did you get them?” Talia and Penelope spent the rest of the break discussing the challenges of ordering the right shoe size online.

A psychiatrist in his 50s came in to present research on schizophrenia. Schizophrenia runs in families. According to the NIMH, “The illness occurs in less than 1 percent of the general population, but it occurs in 10 percent of people who have a first-degree relative with the disorder, such as a parent, brother, or sister.” According to the latest research, a region of the prefrontal cortex (surface area of the brain) is less metabolically active in individuals with schizophrenia. Unfortunately, nobody knows whether this is a cause or effect of schizophrenia. Nonetheless, the psychiatrist suggested screening individuals at risk of schizophrenia with fMRI(functional Magnetic Resonance Imaging) to measure prefrontal cortex activity. If below normal, preventative interventions could be attempted.

After lecture, the psychiatrist talked about his interest in the mental health of incarcerated individuals. “Society is committing genocide against these prisoners, primarily blacks. They develop terrible mental illnesses in childhood. When they become incarcerated these illnesses spiral out of control. It is a sick cycle.” He was lobbying state legislature for more extensive mental health programs in state jails. He also talked why he loves psychiatry. “It is a surreal experience to witness some of these disorders. Bipolar disorder causes patients to swing between fits of mania and extreme depression. We can predict these cycles with almost pinpoint accuracy.”

We had two hour-long lectures on cerebral blood regulation. The brain always needs 750mL of oxygenated, glucose-rich blood per minute. That’s 15 percent of resting cardiac output, which totals roughly 5L per minute. When you begin to exercise, stroke volume and heart rate increase causing a surge in cardiac output to about 12L per minute. How does the brain maintain constant perfusion (blood supply to tissues) while cardiac output varies? The increased pressure is sensed by stretch receptors in arteriole walls of the brain. The increased wall tension causes the arteriole smooth muscle to constrict to relieve this increased wall tension. This myogenic (muscle) response increases the vascular resistance of the brain tissue, thus maintaining the 750mL-per-minute perfusion, and diverting flow to other areas of lower resistance, for example, muscle. The opposite occurs when there is a decreased cardiac output from, from example, hypovolemic shock or cardiac insufficiency.

The two lectures that followed detailed anatomy of cerebral blood supply. The blood supply to the brain originates from the carotid arteries and the vertebral arteries. These form a miraculous structure at the base of the brain called the Circle of Willis. If one contributory artery is blocked, the brain will still get plenty of flow from the others. Doc J commented, “Evolution clearly valued ensuring the brain gets its oxygen and glucose.” The Circle of Willis feeds the six bilateral (left/right) arteries of the brain: left/right anterior cerebral artery (ACA), left/right middle cerebral artery (MCA) and left/right posterior cerebral arteries (PCA). The MCAs supply most of the brain. Unlike other tissues such as muscles, the brain does not have any energy reserves. Without a continuous supply of glucose (or ketones in the fasting state) and oxygen, brain tissue begins to die within minutes. A classmate and his girlfriend are passionate about fitness and supplements. They fast for three days every two months to “reset the system”. He thinks a brain diet of ketones will help prevent Alzheimer’s Disease.

Anatomy lab investigated the contours of the cranial cavity and the main blood structures. Due to time constraints, the instructors decided to perform the time-consuming removal of the brains from our cadavers’ skulls. Next week we will explore “brains in buckets”. Some students were disappointed. “I’ve been looking forward all year to removing the brain.” One of our favorite labs was during the heart unit. We were simply asked to “remove the heart”. A student commented how he found removing the structures that anchors the organ of interest helps build understanding of the anatomic relationships.

With the brains removed, we saw the holes (termed foramina and fissures) in the cranial cavity through which structures such as nerves and blood vessels pass. There are 12 holes per side that we need to know, e.g., foramen magnum (for the spinal cord), superior orbital fissure (optic nerve and ophthalmic artery), foramen rotundum (sensation of the face), and the hypoglossal foramen (nerve to tongue muscles). About half the cadavers still had their Circle of Willis. It looks more like a pentagon. You quickly appreciate how anatomic variations can lead to immense clinical differences for the exact same stroke. Some cadavers have more developed connections within the Circle of Willis (posterior communicating arteries and anterior communicating artery). These individuals would have a less severe stroke with an occluded carotid artery.

My favorite trauma surgeon discussed the two different types of strokes. An embolic stroke is caused by a decrease in blood perfusion to a part of the brain. This is commonly caused by a blood clot traveling up to an artery of the brain or from the slow accumulation of plaque causing stenosis (narrowing) of an artery that supplies the brain. A hemorrhagic stroke is caused by blood leaking out from a vessel, typically from a ruptured aneurysm or prolonged hypertension causing small tears in a capillary bed. We viewed different MRI and CT scans of strokes. She described the “Death-Star” sign. A subarachnoid hemorrhage (“sudden worst headache of your life”) in the Circle of Willis leads to a five-pointed star on CT scan as the blood pools in the contours of the cranial cavity.

A first-year vascular surgeon fellow attended the dissection. He described the carotid endarterectomy, a procedure to treat Atherosclerosis (hardening and narrowing of arteries) and thereby reduce the risk of stroke. The common carotid artery bifurcates into an external and internal carotid artery typically a few centimeters above the thyroid cartilage at a bone called the hyoid bone. The turbulent flow at this bifurcation makes this a high risk site for plaque build-up and intimal (innermost layer of blood vessel) thickening causing stenosis (narrowing) of the internal carotid. The increased blood velocity and shear stress on the plaque wall increase the chance that a small calcium deposit will chip off. As this silent killer travels from the large diameter carotid to smaller arteries, the small deposit begins to enlarge as the body’s clotting system takes over. This blood clot can then get lodged in a small artery. If it gets lodged in the ophthalmic artery, for example, it would causing sudden “curtains to fall” as the retina becomes starved. If it occludes part of the middle cerebral artery, it might cause weakness of the upper extremity and face.

Carotid plaque can decrease overall perfusion pressure to the brain. The Circle of Willis can maintain normal cerebral perfusion pressure with 85 percent stenosis of single internal carotid artery. Above 85 percent, the brain tissue supplied by the end of the main arteries begin to get less flow, leading to a “watershed infarct” with slurred speech and poor comprehension of words.

The carotid endarterectomy is analogous to snaking out a slow bathtub drain. The vascular surgeon detailed the steps while making cuts into a cadaver. He made an incision along the neck exposing the sternocleidomastoid muscle (SCM). The SCM was retracted to reveal the carotid sheath. He opened the carotid sheath and retracted the internal jugular vein and vagus nerve before clamping the carotid arter. In a live patient, he would then have measured the back-flow pressure distal to the clamp. “I need to ensure there is enough perfusion from the Circle of Willis to maintain perfusion of the entire brain without one carotid artery. If the pressure is below about 40 mmHg, I need to create a shunt [install a bypass] of this clamped flow.” He then opened the carotid artery and scraped away some plaque. He gave us the opportunity to feel the vessel. The cadaver’s carotid artery had severe stenosis (greater than 85 percent). The plaque, hard due to the calcium deposits, comes off in sheets. Over half the thickness of the artery was plaque! He then sutured together the carotid vessel incision and closed the wound.

What’s the biggest risk of this stroke-prevention surgery? Postoperative stroke. “It’s impossible to get all the plaque because it goes all along the vessel. You have to decide where to stop.” The surgeon described how he has to ensure that the interior of the artery is smooth. Otherwise these plaque edges will stick out and become dislodged from the shear stress of the blood flow.

The vascular surgeon urged us to follow our interests: “I am still in disbelief I get up every morning and get to perform what I love. It’s just crazy to think about. There is nothing like surgery. Don’t let the amount of time for training turn you off of surgery or any other speciality. Follow your passion.” (Fortunately we’re all in medical school, so the economic consequences of this advice are not as potentially disastrous as following our passion for painting or poetry.)

Our patient case: Jerry, a fit 42-year-old male presenting to the ED for upper extremity weakness and slurred speech. Jerry noticed he had trouble holding his toothbrush before bed. “When I grabbed the cup of mouthwash, I dropped it. I thought to myself, ‘Huh? This is weird.'” I forgot about it and went to bed. When I woke up, my wife said that I was slurring my words. She rushed me to the hospital where everything went black.

Jerry was having a stroke in his MCA. His wife described how furious she was with the doctors. “It seemed like they were just sitting around twiddling their thumbs.” The neurologist added, “Because we did not know when the stroke really set in, we could not use TPA. [Tissue plasminogen activator is a potent clot buster.] Guidelines state that unless you can identify the occlusion occurred within an hour, TPA administration could cause hemorrhagic stroke causing more harm than good.” [A recent article in NEJM recently disputes this time restriction. (http://www.nejm.org/doi/full/10.1056/NEJM199512143332401#t=article).]

Jerry had a relatively minor stroke in a small branch of the left MCA. It still took months to recover from it. He had trouble with his right arms, swallowing and speaking. “I could barely speak for three weeks.” He went to occupational therapy for two months. Most people would now have a hard time realizing Jerry had a stroke. “The main issue I have is that I cannot feel my entire right chest, shoulder and upper back. Some words seem to have just left me. I cannot seem to recall a lot of complicated words.”

“What scares me the most is why this happened. I am a pretty fit person.” The neurologist explained that the Jerry does not have the main risk factors for a stroke. “He does not smoke, does not have afib [atrial fibrillation]. We could not even find an ASD [atrial-septal defect].” He brought up the ASCVD risk estimator to show he was doing pretty well (http://tools.acc.org/ascvd-risk-estimator/). This nagged at Jerry. “I did not know what to tell my two kids.” The neurologist recommended he join a clinical trial with a new drug to prevent strokes. “This clinical trial has given me confidence, even though I don’t know if I am on the drug or the placebo. I just believe it is doing something.” After one year, Jerry will know to which group he had been assigned and, regardless of his original group, will have the option to be on the new drug.

Type-A Anita is soliciting $12,000 in donations on KickStarter for a “historic photo book”. This will contain Anita’s, and others’, photos of protests over the first one hundred days of President Trump. Her Facebook post request contributions from friends and family: “Thank you & Keep Marching!” She has $2,200 pledged.

Statistics for the week… Study: 20 hours. Sleep: 7 hours/night; Fun: 1 night. Example fun: Jane and I took a break from studying and took a boat around a nearby lake with her family. George, a classmate in his late 20s, got engaged over the weekend during a beach getaway. I commented on their Facebook post: “Congrats, Julie, I cannot wait for you to move to here!” This created havoc. Julie, a marriage counselor, had not told her boss that she was moving. She frantically told George to delete the post.

More: http://fifthchance.com/MedicalSchool2020