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NBME 16 Answers

nbme16/Block 1/Question#26 (14.8 difficulty score)
A 16-year-old boy is brought to the emergency ...
Area labeled by the letter 'E'πŸ”,πŸ“Ί

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submitted by bingcentipede(260),

Talking about a boy who lost voluntary movement in his extremities. Thus, his corticospinal tract is injured. It decussates in the medulla, so contralateral limbs are affected. Cross out anything on the left side.

The FA picture is really good with this. Just gotta know E (and F) are the lateral corticospinal tracts.

cassdawg  Tracts are FA2020 p508. +3  
wonkyhonky69  Right, but it said he is unable to move his right side, while the answer was right corticospinal tract. I think we had to realize that this slice was below the level of the pyramidal deccusation. +7  
dermgirl  How can we realize that the lesion was below the level of pyramidal decussation? +  
pruvs  Pyramidal decussation occurs in the caudal medulla. The cross-section given was of the spinal cord (you can see the ventral/dorsal horns). While you wouldn't know where the lesion actually happened, the only plausible answer on the spinal cord section which would result in loss of voluntary movement completely would be the LCSTs (E and F). +1  

submitted by time2swim(0),

I understand that damage to the area labeled E would cause issues with the corticospinal tract. However, wouldnt this damage cause UMN findings as it is before the transition to LMN in the anterior horn? In the stem we read that the pnt has LMN finding of "unable to move" So why are we seeing LMN and not UMN findings? thanks in advance

skilledboyb  Paralysis is a finding common both the UMN and LMN. The distinguishing findings are things like: atrophy (LMN): 30 minute onset not long enough to see this reflex changes, spasticity, etc: not mentioned in the stem +1  

submitted by helen(0),

I chose G. How do you know it's corticospinal tract deficit? Why the deficit not in the ventral horn? somebody plz explain.