PRES is a neurotoxic state that occurs due to difficulties in the cerebral circulations ability to autoregulate in response to acute changes in blood pressure. Hyperperfusion with resultant disruption of the blood brain barrier causes vasogenic edema.  It is most commonly observed in the parieto-occipital regions ( hence the use of the name PRES) although as in this case it is not exclusive to the regions of the brain supplied by the posterior circulation.  It is typically symmetrical as in this case.

The widespread distribution of foci SWI susceptibility in this case with basal ganglia, thalami and brainstem sparing is more consistent with cerebral amyloid angiopathy.  This is opposed to chronic hypertensive angiopathy which has a predonderance for the basal ganglia and thalami.  The SWI appearances are similar representing 'micro-bleeds', but the distribution is different between cerebral amyloid and chronic hypertensive angiopathy.