1. Based on changes in signal on the MRIs, the location of the infarction is in the ventral pons, close to the midline. This is within the territory of paramedian and short circumferential branches of the basilar artery (see Figure 3–3B2).
2. Lower facial muscle control is mediated by a contralateral corticobulbar projection, as is limb muscle control. Therefore, after unilateral lesion of the corticobulbar and corticospinal tracts, there is loss of control of these muscles. By contrast, upper facial muscles and trunk muscles receive more bilateral control, so that after unilateral lesion, there is some residual, redundant, control.
3. After damage to the corticospinal tract, there are plastic changes that result in increased contralateral deep tendon reflexes. This results in abnormal limb posture, increased muscle tone, and difficulty in controlling the weakened limb. Usually these changes present weeks after the injury, but in this patient they occurred immediately after the injury. Further, these changes are most common after damage to the corticospinal tract during development, such as in cerebral palsy, and after spinal cord injury, and less frequent after adult stroke.