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Retired NBME 24 Answers

nbme24/Block 4/Question#48 (reveal difficulty score)
A 55-year-old woman is brought to the ...
Posterior cerebral ๐Ÿ” / ๐Ÿ“บ / ๐ŸŒณ / ๐Ÿ“–
tags: neurology strokes

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 +18  upvote downvote
submitted by โˆ—lsmarshall(465)
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PCA stroke can cause "prosopagnosia" which is the inability to recognize familiar faces. Caused by bilateral lesions of visual association areas, which are situated in the inferior occipitotemporal cortex (fusiform gyrus). The ability to name parts of the face (e.g., nose, mouth) or identify individuals by other cues (e.g., clothing, voices) is left intact.

Without knowing that, remembering occipital lobe is involved in 'visual stuff' broadly, including image processing and this patient is having issues with understanding images should be enough to get to the answer.

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gonyyong  Lol I guessed it exactly because of that +8
sympathetikey  Never heard of that one before. Thanks! +1
karthvee  This is not prosopagnosia, but instead a case of apperceptive agnosia. Wiki: "...patients are more effective at naming two attributes from a single object than they are able to name one attribute on each of the two superimposed objects. In addition they are still able to describe objects in detail and recognize objects by touch." Although, lesions tend to be in the occipito-parietal area so PCA again is the answer! +3
misterdoctor69  I actually think it's both prosopagnosia AND apperceptive agnosia. She is neither able to recognize her mother's FACE nor is she able to recognize objects w/o the help of other senses (apperceptive agnosia) +2
nifty95  Yea couldn't remember the exact name but I just thought of three pathways (visual, somatosensation, and auditory) all converging somewhere/processor (probably somewhere in the temporal lobe...hippocampus?). Beyond the point, the pathways converge to an area which culminates in recognition. Cut off one of the routes (in this case visual), the other two will still work. How is visual cut off? By the PCA not supplying the area leading to neuronal death resulting in varying loss of visual function depending on the area in the occipital lobe. +1



 +5  upvote downvote
submitted by โˆ—poisonivy(39)
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per UWorld Id 2127:

PCA supplies CN III and IV, thalamus, medial temporal lobe, splenium of the corpus callosum, parahippocampal gyrus, fusiform gyrus, and occipital lobe.

Besides the contralateral hemianopia with macular sparing... a PCA stroke can cause contralateral paresthesias and numbness(involvement of lateral thalamus), dyslexia, visual agnosia (impaired visual recognition of objects) and prosopagnosia (inability to recognize faces)

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 +4  upvote downvote
submitted by โˆ—sweetmed(157)
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PCA stroke: Visual Agnosia [can see, but not recognize objects] and Hallucinations, Contralateral hemianopia with macular sparing, Alexia without agraphia[if dominant hemispehere involved].

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 +1  upvote downvote
submitted by futuredoc(15)
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Lesions of the Temporal Lobe:

Superior temporal gyrus: Acoustic agnosia (patient cannot differentiate between sounds) Middle temporal gyrus: Movement agnosia (patient cannot differentiate between the moving and stationary object) Inferior temporal gyrus: supplied by PCA 1. Prosopagnosia (inability to identify the faces) 2. Achromatopsia (loss of color sensation and everything appears gray to them)

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weirdmed51  All temporal gyri supplied by MCA +



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