UW - cerebral watershed infarcts

[osli]

Missed this one in UW this morning and am a little confused. Description was of a watershed infarct, and question asked for the cause.

They listed "hypoxic ischemia" or something very similar as the correct answer. I chose "carotid atherosclerosis".

I understand their explanation that global ischemia leads to the pale infarct described in the watershed zone, but according to RR Path that can be caused by carotid atherosclerosis or thrombosis of a carotid atherosclerotic plaque. It seems like both of these answers are equally true - different ways of saying the same thing.

Was this just a bad question, or did I miss something here? Anyone else remember this question... did I miss an important clue or something in the stem?

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[BusterDO]

Missed this one in UW this morning and am a little confused. Description was of a watershed infarct, and question asked for the cause.

They listed "hypoxic ischemia" or something very similar as the correct answer. I chose "carotid atherosclerosis".

I understand their explanation that global ischemia leads to the pale infarct described in the watershed zone, but according to RR Path that can be caused by carotid atherosclerosis or thrombosis of a carotid atherosclerotic plaque. It seems like both of these answers are equally true - different ways of saying the same thing.

Was this just a bad question, or did I miss something here? Anyone else remember this question... did I miss an important clue or something in the stem?

I haven't seen the question so my explanation is coming from the info you gave and i think the bolded statement is most important. Yes, carotid atherosclerosis can result in an infarct, but that's not the mechanism of the infarct. The global ischemia is what causes the infarct, carotid atherosclerosis, severe hypotension or some other pathology that results in decreased perfusion, causes the global ischemia. In other words, there are multiple pathologies that cause lower perfusion in the brain, but the hypoxemia is the only thing that causes the infarct.

hope that helps.

 

[osli]

I understand your logic but would disagree. That goes against everything I was taught about proximal cause in pathology.

I just went back and looked at this question. In the stem it states that the individual had recently suffered from massive myocardial infarction, so that's the clue that I missed. I missed the key word "massive" in there. I saw MI , which seemed to be perfectly consistent with a systemic atherosclerotic state, and supported the choice of carotid atherosclerosis as the proximal cause of the ischemic infarct. But "massive" is probably a tip-off to a general hypoxic state that was a result of the MI. Subtle, but fair I suppose. Oh - and it was hypoxic encephalopathy not ischemia, of course.

Since only 25% got this one correct, I'm not going to fret much over it. I understand the rationale for both their choice and mine, and that's probably good enough for step 1.

 

[MSKalltheway]

I did that question over the past couple of days also. Like you said, I think the only point of mentioning carotid atherosclerosis was to highlight vascular disease, not so much something for you to directly link it to the watershed infarct due to ischemia, just something to point you towards MI.