MCA stroke and Visual field lesion

[MudPhud20XX]

Kaplan says MCA stroke which accounts 90% of all strokes will give rise to the contralateral homonymous hemianopsia.

1. If you think about the brain region supplied by MCA, it could potentially also give rise to the contralateral superior quadrantanopia, correct?

2. Why would the eyes look toward the side of the lesion? Let's say you have a stroke in the Lt. MCA and you get Rt. homonymous hemianopia, why would your eyes look to the Lt?

Many thanks in advance.

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[Fatalis]

2) if it damages the primary visual cortex no connection is made to the right PPRF [remember it crosses] which activates the ipsilateral CN6 and contralateral CN3. Therefore the eyes will look in the same direction

 

[BrainBuff]

1- The MCA supplies a huge part of the brain and infarcts occur in three major general regions: SUPERIOR DIVISION, INFERIOR DIVISION and DEEP TERRITORY.

If an infarct occurs at the STEM of the MCA you will get a contralateral homonymous hemianopsia (the entire optic radiations are damaged)
If an infarct occurs at the SUPERIOR DIVISION - it will affect the upper portion of the optic radiations in the parietal lobe and will give a contralateral INFERIOR QUADRANTOPSIA ("pie on the floor" visual defect)
If an infarct occurs at the INFERIOR DIVISION - will affect the lower portion of the optic radiations in the temporal lobe and will give a contralateral SUPERIOR QUADRANTOPSIA ("pie on the sky"visual defect)

Note that damage to the PRIMARY VISUAL CORTEX (from a POSTERIOR CEREBRAL ARTERY STROKE) may also cause contralateral homonymous hemianopsias...of different degrees depending on the size of the infarct. (but you should not get quadrantopsias)

2 - If an infarct occurs at the proximal part - (STEM of the MCA) all three regions will be affected. This is the infarct which usually causes contralateral hemiplegia, contralateral hemisensory loss, contralateral homonymous hemianopsia and a global aphasia. There is also IPSILATERAL gaze preference because the FRONTAL EYE FIELD which is on Brodman's area 8 = pre central gyrus is affected. The damage IS NOT on the primary visual cortex and NOT on the PPRF (which is in the brainstem).

A lesion in the primary visual cortex, will not cause gaze preference because it has nothing to do with the PPRF.

🙂

 

[MudPhud20XX]

Thank you so much!!!

 

[aspiringmd1015]

damage to primary visual cortex is just like damaging the optic radiations except for the macular sparing, bc the macula has collater supply via mca if you have a pca stroke. your eyes wont look to the left, bc the frontal eye field is in the frontal lobe, but the only visual fields that you can see is the contralateral visual field.