new_n_lost
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Careful testing of the visual fields in a patient complaining of difficulty reading demonstrates a central scotoma involving one visual field.
This defect is most likely due to a lesion involving which of the following structures?
A. Macula
B. Optic chiasm
C. Optic radiations in the parietal lobe
D. Optic radiations in the temporal lobe
E. Optic tract
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| Jackofknives
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Hmm this contradicts my original knowledge. Scotoma can be associated with meningitis, due to neuritis of the optic nerves, causing edema, and you will see a large optic disc by ophthalmoscope.
If optic nerve is listed, then A macula seem to be the right answer.
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| forumdoctor
Forum Senior
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A
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| new_n_lost
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FORUM RULES-- Those who believe in telekinesis, raise my hand. I get enough exercise just by pushing my luck --P4U World.." The pure and simple truth is rarely pure and never simple."
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| new_n_lost
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The correct answer is A.
The probable location of lesions producing visual defects is a favorite USMLE topic (and is also well worth knowing if you have occasion to work up such a patient). Here is a list that may help you sort through these problems:
Central scotoma ~ macula
Ipsilateral blindness ~ optic nerve
Bitemporal hemianopia ~ optic chiasm (choice B)
Homonymous hemianopia ~ optic tract (choice E)
Upper homonymous quadrantanopia ~ temporal optic radiations (choice D)
Lower homonymous quadrantanopia ~ parietal optic radiations (choice C)
Also, cortical lesions produce defects similar to those of the optic radiations, but may spare the macula.
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FORUM RULES-- Those who believe in telekinesis, raise my hand. I get enough exercise just by pushing my luck --P4U World.." The pure and simple truth is rarely pure and never simple."
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