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NBME 15 Answers

nbme15/Block 4/Question#9 (8.8 difficulty score)
A 40-year-old woman with breast cancer is ...
Occipital lobeπŸ”
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 +2 
submitted by cassdawg(959),

She has left homomynous hemianopia, which can be due to lesion of the contralateral optic tract or as in this case lesion to the contralateral occipital lobe. It is not mentioned explicitly but this causes macular sparing. (FA2020 p542 gives the visual field defects)

bbr  tricky tricky +1  
pontiacfever  Left homonymous hemianopia w/o macular sparing can also occur due to damage to parietal and temporal lobes. But occipital lobe damage is more common. +  
i_hate_it_here  <-- +  
pakimd  macular sparing will only occur if there is an infarct of the posterior coronary artery supplying the occipital lobe. this is because the macular region of the visual cortex has a double blood supply from the middle cerebral artery and the posterior cerebral artery. this woman has breast cancer hence the mets are probably directly to the occipital lobe causing left homonymous hemianopia WITHOUT macular sparing. FA pg 542 look at the illustration: it says number 3 (left homonymous hemianopia WITHOUT macular sparing) and 6 (if PCA infarct when there is left homonymous hemianopia WITH macular sparing) +1