False negative DWI MRI imaging happened in about 7% of cases. If you strongly suspect ischemic stroke clinically, especially posterior stroke, press to admit for further workup.
False negative MRI for stroke
Diffusion-weighted imaging began to be used in 1992 for acute ischemic stroke. This meta-analysis of 12 relevant studies since then found the false negative rate for DWI was 6.8%, occurring most often in the posterior circulation. The gold standard for comparison was clinical diagnosis at discharge in most studies or repeat MRI showing stroke in a few. If the clinical picture is concerning for stroke, admit. DWI is a powerful tool but is fallible. The authors also note that the timing of DWI was late in most of these studies, and the false negative rate may be even higher in very early (<6 hours) MRI for stroke.
Diagnosis of DWI-negative acute ischemic stroke: A meta-analysis. Neurology. 2017 Jun 14. pii: 10.1212/WNL.0000000000004120. doi: 10.1212/WNL.0000000000004120. [Epub ahead of print]
Peer reviewed by Thomas Davis.