When stroke hides: A case of negative diffusion MRI

Ischemic stroke is a medical emergency that's typically identified early using MRI, particularly with diffusion-weighted imaging (DWI). However, some rare but important cases present without the usual DWI findings, posing a diagnostic challenge. We describe the case of a 75-year-old woman with a history of hypertension and diabetes who woke up with weakness on her left side and facial asymmetry. Her initial brain MRI showed no abnormalities on DWI, but ASL imaging revealed reduced perfusion in the right hemisphere, and MR angiography identified an occlusion of the right internal carotid artery. Follow-up CT and MRI scans later confirmed a large right-sided infarct. This case underscores the value of multimodal imaging and the importance of repeating MRI when clinical suspicion for stroke remains high, even if the initial scan appears normal.