macTT
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A 48 year old man comes to the office because his wife noticed that his right pupil is small. Physical exam shows the right is constricted and does not react to light, while his left pupil is normal These findings are most likley to be caused due to a lesion of which of the following structures on the right?
A)Cervical spinal cord
B)Frontal eye feild
C) Lateral geniculate nuclues
D) Optic tract
E)Visual cortex
I am thinking C.....was going to choose A for horner's but there should be other signs as well.....Can someone help me out? Thx
JACK
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| angrydoc
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I would agree with C, but mainly as a process of elimination! You're right - if it was the spinal cord then there would be other signs, not sure what B means, def not the optic tract or he would have visual defect, and nothing to do with the cortex. Any brainy eye-types out there?
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| NE
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I think is sympathetic lesion- the other choices would mean visual fields defect!
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| macTT
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NE,
I was thinking along those lines too however, could it also be lateral gen.? Since it is related to CN III output?
JACK
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| Ancylostoma
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I'm going to have to disagree with c . Tracing the optic pathway shows that the optic tract ends in the lateral geniculate. From there the optic radiations leave to go to the occipital cortex. Thus disrupting the input at that point would prevent the visual cortex from recieveing input and cause a visual field defect. Lesions in the cortex and optic tract would do the same. The frontal eye field is involved in conjugate gaze , a lesion there would not inhibit the reflex but cause a lack of conjugate gaze opposite to the lesion with a slow tracking nystagmus of both eyes toward the lesion. This can be a loss to the sypathetic supply to the eye. Choice is A
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| proctalgia
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Choice A
The lesion must be on Right side according to the Qn.Pupil is small due to the unopposed action of parasympathetic fibers. The reaction of pupils to light is miosis. As the parasympathetic is already activated you will not see any more reaction to stimulation with light.
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| rezaaa
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yeah A the other choices would not produce a miotic pupil....esp lateral geniculate body lesion would definetly produce a visual field defect
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| ashfaque
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answer is A as horner may present like this and presence of other features of horner depends on the site of lesion in cervical sympathetic fibers like proximal or distal to ciliary ganglion .hope this will help ...
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| Dr.Papez
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This question comes up every 3 months I guess.
Had some discussion in this thread
http://www.prep4usmle.com/forum/comments.php?id=3...
Papez
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| NeimanPicksMOM
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oooh my first post..
this is totally A.
I always go by this rule in scenarios like this:
If the pupil is dilated its a CN 3 problem because the job of CN3 is to constrict.
If its constricted it's a Symp problem because the sympathetics are the dilators.
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| Jackofknives
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Pupillary light reflex is a polysynaptic myotatic reflex with following pathway
Optic tract (afferent limb) – interneuron – then to BILATERAL Stinger-Westphal nuclei (right beside CN3 nuclei) – bilateral CN3 nerves (efferent limb) – Ciliary ganglion – constriction of both pupils.
I.E. illumination of one eye results in constriction of both pupils for pts with no neuropathy. This is a myotatic reflex and does not involves the cerebral cortex, ie. B) and E) out.
We have very limited knowledge about lateral geniculate nucleus, and it’s mainly considered a pathway of the visual system with minor functions eg sorting out unnecessary info. So C) is out.
D) is out, bc optic tract lesion results in visual defects, also.
A) is the only one left and makes sense, bc that is where the sympathic pathway lies, which should counteract the function of Stinger-Westphal nucleus. Lesion of the sympathic thus results permanent constriction of the ipsilateral pupil, which is seen in this case.
Answer would be A
Edited by Jackofknives on 03/25/07 - 02:18 PM
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| Summer.Thunder
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interesting, 2 years later, i am doing the same question
and according the answer sheet, it is d
that is why i was confused. i also thought that it was A
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| sigh
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If A is correct we are talking about Horner...Exam questions should be classic prezentation so Honer would be full blown not only miosis.
It looks like it is Argyll-Robertson pupil and the lesion should be in midbrain in circuit for pupillary light reflex.
Here what I found:"Unlike the pathways mediating vision, which involve a synapse in the lateral geniculate body, the pupillary light relex involves a direct pathway to the midbrain from the optic tract"- Goldberg, clinical neuroanatomy...
So the D. can be right answer...I hope somebody else can give more input here because I an confused also...
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| Summer.Thunder
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oh my god, you are right, no one has thought about ar pupil
here is what i found, so the answer is really d
http://www.medscape.com/viewarticle/547645_11
Optic tract damage anterior to the lateral geniculate body (optic thalamus) produces an hemiopic pupillary response so that half of the retina produces a pupil reaction and half does not (Wernicke's sign).[16]
If the direct response is absent but the consensual response is present, then consider:
Neurosyphilis;
Acute glaucoma (see sidebar on glaucoma); or
Medication effect.
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| Jackofknives
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this kind of question will never be presented for your step1 exam because it s vague and incomplete and the presentation is not the classic Argyll-Robertson because the dmg is bilateral and you NEED another sign to confirm the diagnosis - ill let you figure that out  Horner is much more likely.
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| sigh
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Oh you are right Jackofknives! It can'y be A-R because it is not bilateral ...I did read a page about it... the A-R pupil should be also irregular...Does it mean it should be irregular shape?
So, you think Horner... My only wish that you are right about questions like this one not being on the exam. Thanks!
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| spinal shock
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horner syndrome
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| gladiator9
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A
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| supra
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In HORNERS,there is miosis but reaction to light is present.so i still doubt on HORNER'S
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