Our aim was to estimate the prevalence of negative diffusion-weighted imaging (DWI) with total perfusion–diffusion mismatch in a large series of anterior circulation stroke patients treated with thrombolysis and to describe the characteristics of these patients.

From January 2006 to December 2010, a retrospective search was made for total perfusion–diffusion (PWI–DWI) mismatch patterns on pretreatment 1.5-T MRI scans of 166 consecutive thrombolyzed patients taken<4.5h after onset of anterior stroke. A total mismatch profile corresponded to an absence of initial DWI signal changes with hypoperfusion (T_max>6s) on PWI. Clinical and MRI characteristics were compared between DWI+ and DWI– patients.

Five (3%) patients had a normal initial DWI. All had stable substantial clinical deficits (NIHSS scores≥6) and large perfusion abnormalities – in other words, ‘total mismatch’ – and infarcts in the acutely hypoperfused area on follow-up imaging. While DWI– and DWI+ patients did not significantly differ in any of the pretreatment imaging or clinical variables except for the extent of PWI–DWI mismatch, DWI– patients had lower NIHSS scores at 24h, and were more likely to show early neurological improvement (Δ_0–24h NIHSS≥8) and good outcomes (mRS≤2) at the time of hospital discharge.

Total mismatch i.e. failure of DWI to reveal any ischemic tissue despite a large perfusion defect, can be observed before thrombolysis even in stroke patients with stable substantial neurological deficits. However, this rare MRI profile is associated with a favorable outcome after thrombolysis.