Supplementary Material for: Perihaematomal oedema evolution over two weeks after spontaneous intracerebral haemorrhage and association with outcome: prospective cohort study

Introduction
We know little about the evolution of perihaematomal oedema (PHO) >24 hours after ICH onset. We aimed to determine the trajectory of PHO after ICH onset and its association with outcome.
Methods
We did a prospective cohort study using a pre-specified scanning protocol in adults with first-ever spontaneous ICH and measured absolute PHO volumes on CT head scans at ICH diagnosis and 3±2, 7±2 and 14±2 days after ICH onset. We used the largest ICH if ICHs were multiple. The primary outcomes were (a) the trajectory of PHO after ICH onset and (b) the association between PHO (absolute volume at the time when most repeat CT head scans were obtained, and change in PHO volume at this time compared with the first CT head scan) and poor functional outcome (modified Rankin scale 3-6 at 90 days). We pre-specified multivariable logistic regression models of this association adjusting analyses for potential confounders: age, GCS, infratentorial ICH location and intraventricular extension.
Results
In 106 participants of whom forty nine (46%) were female, with a median ICH volume 7ml (interquartile range [IQR] 2-22ml), the trajectory of median PHO volume was an increase from 14ml (IQR 7-26ml) at diagnosis to 18ml (IQR 8-40ml) at 3±2 days (n=87), 20ml (IQR 8-48ml) at 7±2 days (n=93) and 21ml (IQR 10-54ml) at 14±2 days (n=78) (p=<0.001). PHO volume at each time point was collinear with ICH volume at diagnosis (│r│>0.7) but the change in PHO volume between diagnosis and each time point was not. Given collinearity, we used total lesion (i.e. ICH+PHO) volume instead of PHO volume in a logistic regression model of its association at each time point with outcome. Increasing total lesion (ICH+PHO) volume at day 7±2 was associated with poor functional outcome (adjusted OR per ml 1.02, 95% CI 1.00-1.03; p=0.036) but the increase in PHO volume between diagnosis and day 7±2 was not associated with poor functional outcome (adjusted OR per ml 1.03, 95% CI 0.99-1.07; p=0.132).
Conclusion
PHO volume increases throughout the first two weeks after onset of mild to moderate ICH. Total lesion (ICH+PHO) volume at day 7±2 was associated with poor functional outcome but the change in PHO volume between diagnosis and day 7±2 was not. Prospective cohort studies with larger sample sizes are needed to investigate these associations and their modifiers.