Background: Because the pathogenesis of delayed cerebral ischemia (DCI) after subarachnoid hemorrhage (SAH) is unclear, we studied cerebral perfusion at different time points around the occurrence of DCI. Methods: We prospectively enrolled 53 patients admitted to the University Medical Center Utrecht who underwent CT perfusion (CTP) scans on admission, and within 2 weeks after hemorrhage on 2 scheduled time points or during clinical deterioration. The occurrence of DCI was assessed according to predefined criteria by 2 neurological observers blinded to perfusion results. Clinically stable patients (no-DCI) served as reference, and patients with other causes of deterioration (n = 11) were excluded. In DCI patients, the day of DCI onset and in no-DCI patients the median day of DCI onset was taken as t = 0. Scans made before and after DCI were clustered into 5 additional time points. At each time point, cerebral blood volume (CBV) and flow (CBF), and mean transit time (MTT) were measured, and absolute and relative (interhemispheric asymmetry) values were compared between DCI and no-DCI patients. Results: Absolute CBF was lower and MTT was higher in the 18 DCI patients than in the 24 no-DCI patients before, during and after DCI. MTT asymmetry increased during DCI and partially recovered afterwards in DCI patients while it remained constant in no-DCI patients. Absolute and relative CBV remained constant in both groups. Conclusions: Our findings suggest that DCI patients already have diffusely worse perfusion (absolute values) than no-DCI patients before focal worsening (increased asymmetry) occurs and becomes symptomatic. The partial recovery in the measured areas suggests that DCI can be partly reversible.

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