NBME 23 Answers : Block 2 : #25 = A 44-year-old man with invasive pancreatic cancer ...

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submitted by bigbootycorgi(1),

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?

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. +

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 +1

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. +4