60 year old lady presented with blurring of vision of 6 hours duration. Clinical examination revealed left-sided horizontal gaze paresis. She had no other focal neurological deficits. MRI Brain showed acute infarct (hyperintense signals on DW images, as shown above) in the left side of pons, affecting its dorso-medial part.
Horizontal gaze paresis in pontine infarct occurs due to the involvement of abducens nucleus and para pontine reticular formation (PPRF). Abducens nucleus supplies not only the ipsilateral lateral rectus muscle, but also the contralateral medial rectus muscle. So, in this case, infarct on the left side of pons in the region of abducens nucleus has affected left lateral rectus and right medial rectus causing a gaze paresis to the left side. Her symptoms improved and completely resolved on second day of admission.