Ischemic lesion growth in patients with a persistent target mismatch after large vessel occlusion

Background: Failure to reperfuse a cerebral occlusion resulting in a persistent penumbral pattern has not been fully described. Methods: We retrospectively reviewed patients with anterior large vessel occlusion who did not receive reperfusion, and underwent repeated perfusion imaging, with baseline imaging < 6 h after onset and follow-up scans from 16–168 h. A persistent target mismatch (PTM) was defined as core volume of < 100 mL, mismatch ratio > 1.2, and mismatch volume > 10 mL on follow-up imaging. Patients were divided into PTM or non-PTM groups. Ischemic core and penumbral volumes were compared between baseline and follow-up imaging between the two groups, and collateral flow status assessed using CT perfusion collateral index. Results: A total of 25 patients (14 PTM and 11 non-PTM) were enrolled in the study. Median core volumes increased slightly in the PTM group, from 22 to 36 ml. There was a much greater increase in the non-PTM group, from 57 to 190 ml. Penumbral volumes were stable in the PTM group from a median of 79 ml at baseline to 88 ml at follow-up, whereas penumbra was reduced in the non-PTM group, from 120 to 0 ml. Collateral flow status was also better in the PTM group and the median collateral index was 33% compared with 44% in the non-PTM group (p = 0.043). Conclusion: Multiple patients were identified with limited core growth and large penumbra (persistent target mismatch) > 16 h after stroke onset, likely due to more favorable collateral flow.