Strokes can cause many clinical findings including weakness, numbness, changes in
cognition, etc, depending on the location of the stroke
. An MRI of the brain is a very useful modality to identify strokes. If indeed there was a structural lesion (i.e., stroke), it should be seen on the MRI. However, MRIs are only so specific and sensitive for detecting strokes.
I agree your son should continue following up with the neurologist. Neuroimaging would be useful.