Comparative Analysis of Markers of Mass Effect after Ischemic Stroke

Abstract

Background and purpose: Midline shift determined on magnetic resonance imaging (MRI) or computed tomography (CT) images is a well-validated marker of mass effect after large hemispheric infarction and associated with mortality. In this study, we targeted a population with moderately sized strokes. We compared midline shift to other imaging markers and determined their ability to predict long-term outcome.

Methods: MRI scans were studied from the Echoplanar Imaging Thrombolysis Evaluation Trial (EPITHET) cohort. Midline shift, acute stroke lesion volume, lesional swelling volume, change in ipsilateral hemisphere volume, the ratio of ipsilateral to contralateral hemisphere volume, and the reduction in lateral ventricle volume were measured. The relationships of these markers with poor outcome (modified Rankin scale score 3-6 at day 90) were assessed. Receiver-operating characteristic (ROC) curves were generated to compare the performance of each metric.

Results: Of the 71 included patients, 59.2% had a poor outcome that was associated with significantly larger values for midline shift, lesional swelling volume, and ratio of hemisphere volumes. Lesional swelling volume, change in hemisphere volume, ratio of hemisphere volumes, and lateral ventricle displacement were each correlated with midline shift (Spearman r = .60, .49, .61, and -.56, respectively; all P < .0001). ROC curve analysis showed that lesional swelling volume (area under the curve [AUC] = .791) predicted poor outcome better than midline shift (AUC = .682). For predicting mortality, ROC curve analysis showed that these three markers were equivalent.

Conclusion: The ratio of ipsilateral to contralateral hemisphere volume, baseline lesion volume and lesional swelling volume best predicted poor outcome across a spectrum of stroke sizes.

Keywords: Ischemia; brain edema; magnetic resonance imaging; mass effect; stroke.

Figure 1

Illustration of the different imaging markers of mass effect. A) shows the baseline (BL) diffusion-weighted image (DWI) with the stroke lesion outlined in blue. B) shows the coregistered follow-up (FU) DWI with the baseline lesion superimposed in blue. Newly infarcted tissue is outlined in red, and is excluded from the swelling volume measurement. The swelling volume corresponds to the region surrounding the blue baseline stroke lesion outline. C) Outline of the ipsilateral (green) and contralateral (yellow) hemisphere. The relative change in hemisphere volume is the FU hemisphere volume minus the BL hemisphere volume divided by the BL hemisphere volume. The hemisphere ratio is calculated as the FU ipsilateral hemisphere volume divided by the FU contralateral hemisphere volume. D) Outline of the ipsilateral (green) and contralateral (yellow) lateral ventricle volume. An analogous approach as in C) was used to calculate CSF displacement measurements, except that the lateral ventricle volumes were used.

Figure 2

Receiver operating characteristics curves for the discrimination between good and poor outcome. Receiver operating characteristics (ROC) curve analysis showed that swelling volume (A) best discriminated patients with a modified Rankin Scale score of 3–6 at 90 days with an area under the curve (AUC) of 0.79. The AUC for midline shift (B) and the ratio of hemisphere volumes (C) were lower. The difference between the AUC for swelling volume and the AUC for midline shift was significant (p = 0.047).