NBME 20 Spastic hemiparesis on the right (NBME Answers)

Retired NBME 20 Answers

nbme20/Block 1/Question#35 (reveal difficulty score)
A 70-year-old man dies of coronary artery ...
Spastic hemiparesis on the right 🔍 / 📺 / 🌳 / 📖
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+19 upvote downvote
submitted by ∗sympathetikey(1600)

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As stated below, the Left crus cerebri was damaged (see what it should normally look like below). This contains the corticospinal tract. Since the corticospinal tract decusates at the medulla, below the midbrain section we're looking at, you would see Contralateral (Right) Spastic Hemiparesis

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sympathetikey http://what-when-how.com/wp-content/uploads/2012/04/tmp15F11_thumb.jpg +24

hello What identifies that a cross-section is medulla vs midbrain vs pons? +5

kernicterusthefrog @hello I like to pay attention to the Cerebral Aqueduct (diamond/spade shape seen mostly in Midbrain, and transitioning to 4th ventricle in rostral Pons), and then the shape and size of the 4th ventricle as you move down Pons to rostral&middle Medulla, and eventual closing and absence of fluid space at caudal Medulla. +13

hello @kernicterusthefrog Thank you. +

mbourne NGL, I thought the right side had the pathology lmao ty +34

lulumomovicky Damaged area is the cerebral peduncle, which contains the Corticospinal tract --> contralateral hemiparesis. You know this because the upper diamond shape is the cerebral Aqueduct, which indicates you that the slice give corresponds to the Mesencephalon --> where you know you can find Substantia nigra, just by the side of the CEREBRAL penduncles. Don't confuse with CEREBELLAR penducles, which you might see within the pons and the upper part of the medulla oblongata. If these are damaged --> dysmetria, ataxia, dysarthria, etc. +

+8 upvote downvote
submitted by arkanaftus(14)

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Is it appropriate to ask a question about the structure which is absent on the picture? It was super confusing! How can you say it was not a defect of the tissue cut?

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drdoom why did this get downvoted? +

weenathon The missing structure is the cerebral peduncle (also called the crus cerebri). You can tell it is a good slice and not a weird cut because of the symmetry of the rest of the midbrain structures. Everything is symmetrical except the cerebral peduncles, with the left one missing. I also think it's a safe bet to say it's not a random piece of tissue missing because tissue artifact is not one of the choices. +10

+2 upvote downvote
submitted by ∗ibestalkinyo(59)

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The corticospinal tract runs from the cerebral cortex (Pre-Central Gyrus), through the posterior limb of the internal capsule, and into the posterior portion of the brainstem where they form highly myelinated medullary pyramids. These travel down the spinal cord, decussate and synapse of lower motor neurons in the ventral horn of the spinal cord.

A past history of cerebral infarction must have affected this patient's left middle cerebral artery and through Wallerian degeneration, the left medullary pyramid degenerated.

Destruction of the left corticospinal tract before decussation leads to contralateral spastic hemiparesis (since this is an upper motor neuron lesion.

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+2 upvote downvote
submitted by ∗stepwarrior(29)

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The incorrect labeling of the gross pecimen makes this question a bona fide piece of garbage.

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+1 upvote downvote
submitted by ∗strugglebus(189)

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It affected the corticospinal tract in the crus cerebri on the L

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+0 upvote downvote
submitted by failingnbme(3)

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scary crying old ostrich man that's all I can see :O

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-10 upvote downvote
submitted by ∗hayayah(1212)

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The damage is in the L midbrain in the area affecting the corticospinal tract. Because it is in the midbrain, decussation in the pyramids (medulla) so it will show ipsilateral dysfunctional motor signs.

Photo of midbrain and important areas: shorturl.at/myHLR

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masonkingcobra Just for clarification, on the left side, you see where he had the infarction 7 years ago and the tissue is gone. +9

chefcurry so is the dysfunction on the contralateral side? +

praderwilli If the decussation is in the pyramids of the medulla, shouldn't it be contralateral hemiparesis if the damage is on the right? It confuses me because of the labeling right and left at the top of the pictures. +

endochondral1 that link isnt working @ hayayah....is there any good picture to look at to know where the tracts are on this section? +1

emsports01 http://what-when-how.com/neuroscience/brainstem-iii-the-midbrain-organization-of-the-central-nervous-system-part-1/ +

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