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NBME 21 Answers

nbme21/Block 3/Question#27 (36.4 difficulty score)
A 55-year-old woman with a benign nodule in ...
External carotid🔍
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 +18 
submitted by hayayah(990),
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heT odhirty is sideulpp iwth treirlaa bdolo orfm eth epuisorr itydorh yrr,tea a ahcnrb fo het ealnetrx oirdtac ytrrae, dna hte eiifronr doyrhit ,reaytr a arhbnc of het rccyilarevoht u.tnkr

sahusema  https://imgur.com/0uBvexe +6  



 +2 
submitted by sharpscontainer(5),

I was duped; did anybody here get it wrong because they thought about the thyroid ima artery arising from the brachiocephalic trunk? No? Just me? Okay.

peridot  Ooh that is tricky tricky. In the question stem they said they already ligated that one ("a branch of the brachiocephalic trunk") and were wondering what else needs to be ligated in addition to that. Therefore the answer is the superior thyroid artery, which is coming from the external carotid. I don't think I knew any of this when I did the question though, cause I had to google all this just now. +1  
anechakfspb  In the stem they said they ligated a branch of the thyrocervical trunk, not the brachiocephalic. According to Wiki, the thyroid ima artery (which does arise from the brachiocephalic trunk) is only present in about 3-10% of the population. Therefore, while technically this answer could be correct, external carotid is "more correct". Source: https://en.wikipedia.org/wiki/Thyroid_ima_artery +1