A small but significant percentage of patients with acute ischemic stroke (AIS) had a negative diffusion-weighted imaging (DWI) scan, a recent study found. In addition, patients with neurologic deficits consistent with posterior circulation ischemia have 5 times the odds of having a negative DWI scan compared to patients with anterior circulation ischemia. Researchers systematically searched relevant studies between 1992 and 2016. Studies were included based upon enrollment of consecutive patients presenting with a clinical diagnosis of AIS prior to imaging. Meta-analysis was performed to synthesize study-level data, estimate DWI-negative stroke prevalence, and estimate the odds ratios (ORs) for clinical characteristics associated with DWI-negative stroke. They found:

• 12 articles including 3,236 AIS patients were included.
• The meta-analytic synthesis yielded a pooled prevalence of DWI-negative AIS of 6.8%.
• In the 5 studies that reported proportion data for DWI-negative and DWI-positive AIS based on the ischemic vascular territory (n=1,023 AIS patients), DWI-negative stroke was strongly associated with posterior circulation ischemia, as determined by clinical diagnosis at hospital discharge or repeat imaging.