Inverse mismatch and lesion growth in small subcortical ischaemic stroke

Infarction typically develops within the borders of an initial hypoperfused tissue. We prospectively investigated whether in small subcortical stroke patients infarct growth can occur beyond the margins of the affected vascular territories. In 19 consecutive patients, stroke MRI was performed within 14 h after ictus, and at days 2 and 6 (+/- 1). Size of diffusion and perfusion disturbances were determined. Infarct volume measured on T2-weighted images on day 6 was considered as imaging endpoint. At the initial examination, the mean diffusion lesion [apparent diffusion coefficient (ADC) lesion size, 1.82 +/- 1.2 ml] was larger (p = 0.0002) than the perfusion lesion [mean transit time (MTT) lesion size, 0.72 +/- 0.69 ml]. Such an "inverse mismatch" (ADC lesion > MTT lesion) was present in 14/19 patients at baseline and in all patients on day 2. Final lesion volume at day 6 was 3.2 +/- 1.6 ml which was larger than the initial perfusion deficit (p = 0.02). In small subcortical ischaemic stroke "inverse mismatch" is frequent and infarction develops beyond the initial perfusion disturbance. This indicates that cytotoxic processes probably triggered by the infarct core are a dominant mechanism for lesion growth. Areas with normal perfusion but which are threatened by cytotoxic damage developing over several days seem prime targets for neuroprotective therapy.