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NBME 24 Answers

nbme24/Block 4/Question#6

A 68-year-old woman comes to the physician because ...

Inferior mesenteric and superior mesenteric

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The presentation here seems to fit that of mesenteric vascular occlusion- postprandial pain that lasts 1 hour, food aversion, weight loss. The patient also has risk factors associated with mesenteric vascular occlusion- older than 60 years old, Hyperlipidemia, Hypertension, PMHx.

"The mesenteric circulation consists of three primary vessels that supply blood to the small and large bowel: the celiac artery, superior mesenteric artery (SMA), and inferior mesenteric artery (IMA). Blood flow through these arteries increases within an hour after eating due to an increase in metabolic demand of the intestinal mucosa.Chronic occlusion of a single vessel allows collateral blood flow to compensate, thus symptoms do not typically present until at least two primary vessels are occluded." https://www.ncbi.nlm.nih.gov/books/NBK430748/

Collaterals between SMA and IMA near the splenic flexure (Meandering Mesenteric artery). There is also collateral between Celiac Artery and SMA (Pancreaticoduodenal arcade).

Lastly, I know that there is a 3-cm ectatic aorta found on CT, but an aortic aneurysm would not produce these symptoms. Even if you thought that the symptoms were due to the AAA, you could still get to the correct answer if you use fahmed14's reasoning.

honey-crusted lesion  Great explanation! There's also a slide about this in the 100 Anatomy Concepts pdf but doesn't go into as much detail as this explanation. Thanks! +  
djtallahassee  Good explanation but I think an AAA would be more likely superior mesenteric and hepatic. the SMA and IMA are more than 3 cm apart (L1 to L4ish), Triple A affecting both would be very large. I blew this question because I saw 3cm and jumped to AAA, didnt even see it was a sclerosis thing. Put the two closest arteries and moved on +  

 +4  upvote downvote
submitted by fahmed14(19),

The 3-cm ectatic aorta means she has an abdominal aortic aneurysm. Generally, they tend to occur below the renal branches so I went with the two closest branches- SMA (slightly above renal) and IMA (below renal). Also, splenic flexure is a common watershed area supplied by SMA and IMA so involvement of both can cause her symptoms

 +2  upvote downvote
submitted by usmle11a(36),

the only thing made me choose IMA and SMA is the fact they supply the intestine which is the common site for ischemic mesenteric disease.

all the other vessels, either have collateral supplies or they supply to organs with multiple sources of blood supply

IMA and SMA both have collaterals with each other (marginal arteries and meandering arteries), so incase there is involvement of one of the arteries the blood supply from other can prevent ischemia.

but if both SMA and IMA are involved it would result in ischemia and symptoms described in the question.

 +0  upvote downvote
submitted by mousie(128),

looking back at this Q I notice that the patient also has hypertension ...could that have been a clue to include the SMA bc its so close to the renal arteries (Renal a stenosis)?

nwinkelmann  I didn't know how to approach this either, but now this is my thought process: Patient has pain after eating. If it's not due to an ulcer (which is the only thing I could come up with because I didn't know what else it was talking about), why would eating cause pain? Well... eating causes increased GIT activity which means increased blood flow. As you pointed out, the patient has HTN and CAD, indicating likely extensive atherosclerosis. This is important because why would eating leading to increased blood flow cause pain, when usually it doesn't? Well... atherosclerosis in the heart leads to stable angina. This presentation sounds like a "stable angina" of the abdomen. +  

Why are the IMA and SMA most likely to be affected in her condition?

sattanki  Again, not too sure, but I think they were describing a patient with chronic intestinal angina, which is classically from atherosclerosis of the IMA/SMA. +1  
mcl  I was also thinking about which areas have crappy blood supply (watershed areas), which I assume would be worse off in the case of chronic mesenteric ischemia. If you look on page 357 of FA 2019, SMA & IMA at the splenic flexure is a watershed area; the other is rectosigmoid junction (sigmoid branch from IMA and superior rectal). +  

if the option had SMA and celiac trunk, would that be correct?

One way to look at this would be to go back to pathogenesis of fatty streaks. They are most commonly found at the aortic bifurcation, so basically the lower down you go down the abdominal aorta, more turbulent the flow, causing higher potential for atherosclerosis and stenosis of branch vessels. Also, renal artery stenosis is well described which is given off after the celiac trunk so safe to say celiac trunk is spared in any kind of atherosclerotic stenosis.

Chronic Mesenteric Ischemia aka intestinal angina. Main clues are postprangial epigastric pain, weight loss. Usually due to Celiac (a), SMA, or IMA atherosclerosis.

neonem  What's tough about these answer choices though is that you have 2 different viable combos. +  
codyluvr95  The ectatic aorta might also mean AAA below the renals, affecting the IMA, +2  
sherry  Also since there is this ectatic aorta, the arteries involved need to be adjacent to one another. If there is a choice as in celiac and SMA, it could also be correct. +