Sensitivity and interrater agreement of CT and diffusion-weighted MR imaging in hyperacute stroke

Abstract

Background and purpose: Previous acute stroke studies found diffusion-weighted (DW) imaging superior to CT for detection of early ischemic signs (EIS). However, these findings were confounded by a large time interval in favor of DW imaging. We compared DW images and CT scans obtained with a short time delay in patients with acute stroke to define the sensitivity and interrater agreement of both imaging techniques.

Methods: CT scans and DW images were obtained within 6 hours of symptom onset in 46 patients with acute stroke. Three neuroradiologists and three neurologists reviewed the images for EIS in five regions of the middle cerebral artery (MCA) territory and estimated the extent of EIS (< or > one-third of the MCA territory).

Results: The mean delay between imaging with both modalities was 24.5 minutes (range, 10-41 minutes). Forty-five of 46 patients had an ischemic stroke. EIS were seen on 33 of 45 CT scans (73% sensitivity; 95% confidence interval [CI]: 58-85%) and on 42 of 45 DW images (93% sensitivity; 94% CI: 82-99%). Interrater agreement was moderate (kappa = 0.57) for CT and excellent (kappa = 0.85) for DW imaging. CT studies had a moderate interrater agreement for estimation of EIS greater than one-third of the MCA territory (kappa = 0.40), whereas DW imaging showed good results (kappa = 0.68). Sensitivity for detection of greater than one-third of the MCA territory was equally poor (57%, 95% CI: 29-82%) for both CT and DW imaging.

Conclusion: DW imaging helped identify EIS with higher sensitivity than that of CT. The interrater variability of the one-third rule was high for CT, and thus the clinical applicability of CT is limited. Our results support the application of stroke MR imaging for the treatment of patients with acute stroke.

Fig 1.

Case of a 62-year-old patient with aphasia and right hemiparesis. (A) CT scans obtained 100 minutes after symptom onset, (B) DW images obtained 120 minutes after symptom onset, and (C) follow-up FLAIR images. DW images were rated positive by all raters and show hyperintensity in the left MCA territory. CT scans were rated normal by five of the six raters. With the knowledge of the DW images, there might be a subtle hypoattenuation in the left insular ribbon region on CT scans. However, the follow-up FLAIR images reveal only small ischemic leasons of the left insular ribbon and parietal regions, with normalization of large parts of the former diffusion-restricted area.

Fig 2.

Case of a 35-year-old patient with left hemiparesis and neglect. (A) CT scans obtained 80 minutes after symptom onset, (B) DW images obtained 115 minutes after symptom onset, and (C) follow-up FLAIR images. Five of the six raters recognized parenchymal hypoattenuation of the right insular ribbon and frontotemporal regions on the CT scans. DW images and follow-up FLAIR images after 7 days illustrate a right MCA stroke caused by an MCA trunk occlusion.