Diffusion-weighted imaging: not all that glitters is gold.

South Med J 102(9):923-8 (2009) PMID 19668055

Diffusion-weighted imaging (DWI) is a sophisticated magnetic resonance imaging (MRI) technique with rapid acquisition time and high sensitivity for depicting acute cerebral ischemia. It is currently part of the routine workup in most medical centers when ischemic stroke is in the differential diagnosis. DWI helps establish a diagnosis of acute ischemic infarct even in cases where the clinical presentation is not typical for ischemic stroke. However, contrary to popular belief, not every hyperintensity on DWI is an ischemic stroke. Consequently, DWI with high intensity signals, commonly called "positive" DWI, is sometimes misinterpreted and leads to incorrect medical management. In this report, we briefly discuss some of the essential, technical aspects of DWI and report various clinical scenarios, which may lead to "positive" DWI findings but are not ischemic strokes. Although the sensitivity of DWI for ischemic stroke is very high, the specificity is not as high, and a "positive" DWI does not exclude other diagnoses that should be considered based on each patient's clinical history and examination, and the appearance of other sequences of MRI scans.