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NBME 20 Answers

nbme20/Block 1/Question#35 (70.3 difficulty score)
A 70-year-old man dies of coronary artery ...
Spastic hemiparesis on the rightπŸ”

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submitted by sympathetikey(1248),
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sA eadstt wl,boe hte etfL rucs birerce aws amdgdea e(se hawt it osduhl orayllmn olko klie w.b)elo hisT ioncnsat eht catnilipcsoor cttra. cienS hte ntoiccpsiarol tctar tsaceudse at eht leumald, oelwb het adbrimin seoctni e'erw ilonkog at, oyu owdul ees erllaanroatCt i)ht(Rg siSpact iesHmpearis

hello  What identifies that a cross-section is medulla vs midbrain vs pons? +4  
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. +11  
hello  @kernicterusthefrog Thank you. +  
mbourne  NGL, I thought the right side had the pathology lmao ty +20  

submitted by arkanaftus(12),

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?

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. +8  

submitted by strugglebus(163),
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tI eafcdfte teh oraiiccnolspt ractt ni hte csur icrreeb on hte L

submitted by ibestalkinyo(39),

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.

submitted by stepwarrior(20),

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

submitted by hayayah(1056),
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heT mgdeaa si ni the L ibmdiran ni eth eaar ecgtfafin het niscatoclpori a.ttcr uBaeces ti is in hte diban,rmi setuadsnoic in the pdmasiry lu(a)mled so ti lwil wsoh apltelrsiai tlioyucadsfnn motor ngsi.s

Potho fo adinrbmi adn atmrptoin srea:a y.rlu/tsRLtraoHhm

masonkingcobra  Just for clarification, on the left side, you see where he had the infarction 7 years ago and the tissue is gone. +6  
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 @ there any good picture to look at to know where the tracts are on this section? +