INO Lesion

[ray656712]

Alright, I've never had any issues with INO stuff, but this Uword qustion (12083) has me confused..I'm likely overthinking.

The pictures shows the patient's LEFT eye unable to ADduct during RIGHT gaze.

The answer was RIGHT dorsal paramedian pons lesion. In the explaination, it says lesions to the RIGHT dorsal paramedian pons can disrupt the RIGHT MLF, resulting in impaired ADduction of the RIGHT eye during LEFT conjugate horizontal gaze. (which was not our patient's problem...his problem was the left eye unable to ADduct)

So a few questions

1. Why would a RIGHT paramedian pontine lesion disrupt the RIGHT MLF? CN6 nucleus is in the dorsal pons, but it projects to CN3 nucleus via the LEFT MLF

2. I agree that disruption of the right MLF results in impaired right eye ADduction during left gaze....but that was not the issue in the question.....so what am I missing?

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[Eremba]

I just had this question today!! And the explanation is also confusing me. I am wondering if the explanation is just incorrect?


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[ray656712]

I just had this question today!! And the explanation is also confusing me. I am wondering if the explanation is just incorrect?


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Glad I'm not the only one! I spent probably over two hours looking at this haha. The best thing I could come up with was that there was a typo in the explanation. (Should have said a lesion in the right paramedian pons can disrupt the LEFT MLF > LEFT eye cant look RIGHT). That would make sense, and would still make the answer correct.

Because I guess if you hit the dorsal pons where the CN6 nucleus is, you could theoretically hit the left MLF tracts as they are leaving. Ill attach a picture.

Any thoughts?

 

[fulltimeaerobe]

Lol here for the same reason. The example in first aid (2016, pg 490) is actually the same diagnosis but the picture shows inability to adduct during leftward gaze, not rightward as shown in the question.

It looks like they updated the question 4 days ago so maybe it's a typo they'll get around to fixing on Monday?

 

[fulltimeaerobe]

Glad I'm not the only one! I spent probably over two hours looking at this haha. The best thing I could come up with was that there was a typo in the explanation. (Should have said a lesion in the right paramedian pons can disrupt the LEFT MLF > LEFT eye cant look RIGHT). That would make sense, and would still make the answer correct.

Because I guess if you hit the dorsal pons where the CN6 nucleus is, you could theoretically hit the left MLF tracts as they are leaving. Ill attach a picture.

Any thoughts?

No wait you're totally right. I can see this being a question where you wish left MLF was an answer choice but it's actually a paramedian pontine injury like you have in your drawing.

So I guess:
Right PPRF coordinates left eye adduction via the left MLF, right abduction via CN VI. Lesion --> inability to adduct the left eye durirng right gaze
Left PPRF controls right eye adduction via right MLF, left abduction via CN VI. Lesion --> inability to adduct right eye during left gaze
(Abducens not affected in PPRF injuries since it has its own nucleus ventral to the PPRF.)

 

[ray656712]

No wait you're totally right. I can see this being a question where you wish left MLF was an answer choice but it's actually a paramedian pontine injury like you have in your drawing.

So I guess:
Right PPRF coordinates left eye adduction via the left MLF, right abduction via CN VI. Lesion --> inability to adduct the left eye durirng right gaze
Left PPRF controls right eye adduction via right MLF, left abduction via CN VI. Lesion --> inability to adduct right eye during left gaze
(Abducens not affected in PPRF injuries since it has its own nucleus ventral to the PPRF.)

Yeah, I believe that's correct. So I guess it was a typo in the explanation then! I would say I wasted a few hours trying to figure this out, but I guess if anything, I learned these lesions a bit better in the process Thanks guys

 

[Eremba]

Yeah, I believe that's correct. So I guess it was a typo in the explanation then! I would say I wasted a few hours trying to figure this out, but I guess if anything, I learned these lesions a bit better in the process Thanks guys

Haha. Yes. I spent ample time on google trying to find a picture explanation that made sense. It was infuriating!!!

I am so glad I am not alone!


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