- MRI evidence of S3 that is >=2.0 cm in diameter if DWI/bright lesion on FLAIR/T2 or <=1.5cm hypointense lesion on FLAIR/T1, corresponding to the qualifying event (required for all brainstem events) OR multiple S3 in cerebral hemispheres of <=1.5cm hypointense lesions on FLAIR/T1 AND absence of cortical stroke and large subcortical stroke.