Registrar: "Where is it?" Me: "Left lateral medulla." Registrar: "The scan is not back." Me: "The scan is going to agree with me." Registrar: "And if it does not?" Me: "Then the scan is early." Send this to whoever still examines before they scan.

EXPLAINED (ACCURACY-CHECKED)

Early diffusion-weighted MRI can be falsely negative in acute ischaemic stroke, and false negatives are disproportionately reported in posterior circulation and brainstem infarcts, so a negative early scan does not exclude a clinically localised lesion.