Why is there ipsilateral gaze preference in middle cerebral artery stroke?

The middle cerebral artery (MCA) can be divided into 2 main territories, the superior and inferior. If MCA stem is occluded, this will results in complete MCA syndrome which one will be presented with hemiplegia, hemisensory loss, hemianopsia, temporary ipsilateral gaze palsy, and global aphasia (if on dorminant side) or hemi-neglect (non-dorminant). If the superior division is blocked, the victims will be presented with contralateral hemiplegia, hemisensory loss, temporary ipsilateral gaze palsy, Broca’s aphasia (dorminant side). If the inferior division is affected, one will have Wernicke’s aphasia (dorminant), contralateral homonymous superior quadrantanopia, and hemi-neglect or spatial agnosia (non-dorminant).

It is known why such syndrome presence dues to the existence of primary motor and sensory cortex, Broca’s and Wernicke’s area. How about temporary ipsilateral gaze palsy?

This involved the Brodmann’s area 8, which is located anteriorly to area 6. This area is known as frontal eye field. Other name given includes frontal center for adversive and contraversive eye movement. This area is involved when the a person responds to the instruction “turn your eyes to the left; or right. When this area (one side) is stimulated, there will be a conscious repetitive conjugate eye movement to the opposite side. Bilateral stimulation results in conjugate eye movement in upwards direction.

20130408-220207.jpg
Image above shows the Brodmann’s area with (A) lateral view and (B) medial view. Image is obtained from [ref2]

Hence, if this area is damaged, you might now know it, there will be a transient paralysis of voluntary conjugate gaze to the contralateral visual field and ipsilateral conjugate deviation of the eyes, towards the MCA strokes side. This is why such presentation occurs in total MCA strokes and superior division stroke but not the inferior division.

This post is dedicated to my friend, Dexter Lai.
References
1. Louis R. Caplan, ed. Caplan’s Stroke: a clinical approach. Fourth edition. Elsevier Saunders, Philadelphia. PA. 2009.
2. Elliott L. Mancall and David G. Brock, ed. Gray’s clinical neuroanatomy: the anatomical basis for clinical neuroscience. First edition. Elsevier Saunders, Philadelphia. PA. 2011.
3. Stanley Jacobson and Elliott M. Marcus, ed. Neuroanatomy for neuroscience. Springer, Boston. MA. 2008.
4. Stephen L. Hausser. Ed. Harrison’s neurology in clinical medicine. 2nd edition. McGraw Hill. New York, NY. 2010

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