NBME 23 Area labeled ‘H’ (NBME Answers)

Retired NBME 23 Answers

nbme23/Block 2/Question#25 (reveal difficulty score)
A 44-year-old man with invasive pancreatic ...
Area labeled ‘H’ 🔍 / 📺 / 🌳 / 📖
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submitted by ∗sympathetikey(1600)

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Pain & temperature fibers for the right side come in on the dorsal right side, cross at the anterior white commisure, and travel up in the Spinothalamic tract.

https://lh3.googleusercontent.com/-B4YXuXT68ts/V2Wu-kGlZyI/AAAAAAAAljk/3j2iHrI9hQ4/s640/blogger-image--1680479964.jpg

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focus The diagram here is pretty great, too, for the spinothalamic tract (and it is presented side by side with the dorsal column for comparison): https://opentextbc.ca/anatomyandphysiology/chapter/14-2-central-processing/ +

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submitted by ∗lispectedwumbologist(122)

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We're viewing this slice of the spinal cord from the bottom right? The left right labels always mix me up.

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mcl Yeah, I just stared at this again for a solid 5 minutes straight up dying. I think if we're going with the L/R labels as they are shown on the image, imagine the patient lying on their stomach with their feet pointed towards you and it should make sense. +10

ankigravity But why would anyone ever view a patient like that? I mean, in the era of Covid and proning, maybe. +

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submitted by ∗anechakfspb(77)

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Also you can extrapolate that the fibers causing his pain have already crossed over because this is a cervical spine section, and the pain he's having is thoracic/lumbar

Here's a picture that really helped: https://www.google.com/search?q=cervical+vs+thoracic+vs+lumbar+spinal+cord+slices&rlz=1C1CHBF_enUS801US801&sxsrf=ALeKk003suIj4Gt8w_cxQguy33bsJi7w3g:1590347215846&source=lnms&tbm=isch&sa=X&ved=2ahUKEwjSqfqGmc3pAhXldN8KHUIlDYoQ_AUoAXoECA0QAw&biw=1280&bih=864#imgrc=EMrFYHUe8M5ReM

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submitted by bigbootycorgi(5)

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The thing is, the spinothalamic tract crosses 2 vertebral levels up and then decussates at the anterior white commissure to get from the right to the left, so how do I know which vertebral level I'd be working on this guy?

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chris07 I think the assumption here is that we are dealing with the cord section at the level of the problem. The picture is incredibly misleading. You have to orient yourself. The dorsal columns F, E, A, B are facing the patient's posterior. Once you properly orient it in 3D space, you know that what's labeled "right" is actually the patient's left, and what's labeled "left" is his right side. Super confusing. +2

sne The input arises in a limb/part of body at the level of lesion, enters through the dorsal root (pictured between A and B), decussates and ascends at the anterior commissure, and finally synapses on the second order neuron in the lateral spinothalamic tract. So the spinothalamic tract is responsible for contralateral pain and temperature sensation. So AT THE LEVEL technically would be in the dorsal column +13

nwinkelmann also, @chris07, I think you're wrong about the labels being wrong on the image. Becuase the spinothalamic tract = contralateral pain and temperature, and the patient's pain is on the right side, you would want to target the left spinothalamic tract for pain relief, i.e. the area labeled H. The area labeled D would be the right spinothalamic, purely because that is how the image is labeled. If you assume the label is different, you will get it wrong. +12

kpjk @sne I don't think entering from the dorsal root would be between A and B. It would be part of the gray matter so, lateral to B and F +3

ih8payingfordis I think the key thing here is to recognize that the cross section we're looking at is a CERVICAL section, which means it's definitely higher than the source of pain (back and abdomen). That tells you that the tract must have crossed already so you target the contralateral side. Here is a good link to identify where the cord is from (cervical, thoracic, lumbar and sacral): https://nba.uth.tmc.edu/neuroanatomy/imgsSwfs/L04P08F1.png +4

If you assume that because the pt has R-sided back and ab pain somewhere in the lower thoracic, and you know that this slice of cord is above that because it has a posterior intermediate sulcus present (i.e. has both a gracilus and cuneatus track), then you know that the spinal cord slice is likely above where the pain is, therefore the spinothalamic has crossed over already.

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submitted by ∗donttrustmyanswers(74)

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What is the area labeled 'G' and 'C'? And more characters?

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alexxxx30 lateral corticospinal i think +5

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submitted by alexv0815(10)

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you are looking at this bottom up (as if person is on stomach) so L is patient L and R is patient R. This has cuneate and gracilis tracts, which means it is higher up in thoracic spinal cord and so the spinothalamic has already entered and crossed. So the pathway is from the dorsal root ganglion on R side -> crosses AWC -> goes up to brain at left "H".

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submitted by ∗handsome(3)

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FA 2020 PG 508 he specifically points to right ascending lateral spinothalamic tract bet. sacral cervical ---for pain and temperature

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