Computed tomography grey-white matter ratio at the basal ganglia level in a reference population for hypoxic ischaemic encephalopathy after cardiac arrest - A cross-sectional observational study.

Introduction: A grey-white matter ratio (GWR) < 1.10 at the basal ganglia level on head computed tomography (CT) previously predicted poor outcome with high specificity and moderate sensitivity in cardiac arrest patients. Data on GWR in reference populations are lacking. We explored GWR in a reference group to a cardiac arrest population and hypothesised that none would have GWR < 1.10.

Methods: A retrospective cross-sectional single-centre study. Patients with CT for suspected stroke or transient ischaemic attack were screened between January-August 2021 and included based on matching age and sex to cardiac arrest populations. CTs with pathologic findings were excluded. Circular regions of interest (ROIs) of 0.1 and 0.2 cm² were placed by three raters at the basal ganglia level and GWR was calculated. Bland-Altman plots estimated interrater variability of GWR from 0.1 and 0.2 cm² ROIs.

Results: 155 participants were included. The mean age was 75 years, and 59 % were male. No measurement resulted in GWR < 1.10. Median GWR for all raters ranged between 1.30-1.32 in 0.1 cm² ROIs and 1.27-1.32 in 0.2 cm² ROIs. The lower and upper limits of agreement between raters were around 0.1. The 0.2 cm² ROIs GWR achieved smaller limits of agreement compared to the 0.1 cm² ROIs GWR. Attenuation measurements and GWR differed depending on ROI size used.

Conclusion: A GWR at the basal ganglia level below 1.10 is very unlikely in elderly patients without HIE, suggesting that this may provide a relevant cut-off for HIE prognostication in cardiac arrest patients.