Quantitative Analysis of the Loss of Distinction Between Gray and White Matter in Comatose Patients After Cardiac Arrest

Abstract

Background and Purpose-Anecdotal reports suggest that a loss of distinction between gray (GM) and white matter (WM) as adjudged by CT scan predicts poor outcome in comatose patients after cardiac arrest. To address this, we quantitatively assessed GM and WM intensities at various brain levels in comatose patients after cardiac arrest. Methods-Patients for whom consultation was requested within 24 hours of a cardiac arrest were identified with the use of a computerized database that tracks neurological consultations at our institution. Twenty-five comatose patients were identified for whom complete medical records and CT scans were available for review. Twenty-five consecutive patients for whom a CT scan was interpreted as normal served as controls. Hounsfield units (HUs) were measured in small defined areas obtained from axial images at the levels of the basal ganglia, centrum semiovale, and high convexity area. Results-At each level tested, lower GM intensity and higher WM intensity were noted in comatose patients compared with normal controls. The GM/WM ratio was significantly lower among comatose patients compared with controls (PϽ0.0001, rank sum test). There was essentially no overlap in GM/WM ratios between control and study patients. The difference was greatest at the basal ganglia level. We also observed a marginally significant difference in the GM/WM ratio at the basal ganglia level between those patients who died and those who survived cardiac arrest (Pϭ0.035, 1-tailed t test). Using receiver operating characteristic curve analysis, we determined that a difference in GM/WM ratio of Ͻ1.18 at the basal ganglia level was 100% predictive of death. At the basal ganglia level, none of 12 patients below this threshold survived, whereas the survival rate was 46% among patients in whom the ratio was Ͼ1.18. The empirical risk of death was 21.67 for comatose patients with a value below threshold. Conclusions-The ratio in HUs of GM to WM provides a reproducible measure of the distinction between gray and white matter. A lower GM/WM ratio is observed in comatose patients immediately after cardiac arrest. The basal ganglia level seems to be the most sensitive location on CT for measuring this relationship. Although a GM/WM ratio Ͻ1.18 at this level predicted death in this retrospective study, the difference in this study is not robust enough to recommend that management decisions be dictated by CT results. The results, however, do warrant consideration of a prospective study to determine the reliability of CT scanning in predicting outcome for comatose patients after cardiac arrest. (Stroke.

Useful Computed Tomography Score for Estimation of Early Neurologic Outcome in Post-Cardiac Arrest Patients With Therapeutic Hypothermia

“…Table 1 also presents data for ASPECTS-b, GWR, and QRA according to neurologic outcome. There was no difference in the GWR in the basal ganglia (P=0.101), centrum semiovale (P=0.970), and high convexity (P=0.774) between the 2 groups, and the mean GWR did not signifi- 14 However, the present study showed that GWR was not a significant outcome predictor for postcardiac arrest patients. This apparent discrepancy may be due to the early CT acquisition time frame (within 6 h, and usually around 2 h) in the present study, unlike in previous studies.…”

“…12 Previous studies of post-cardiac arrest patients using brain CT have focused on the gray:white matter ratio (GWR). 13, 14 Few studies have focused on quantifying the extent of brain injury using brain CT. 15 The Alberta Stroke Program Early CT Score (ASPECTS) P ost-resuscitation status after cardiac arrest is a clinical model of hypoxia-ischemia injury. 1,2 Postresuscitation care including therapeutic hypothermia (TH) for neuroprotection is based primarily on recognition of brain damage.…”

Post–Cardiac Arrest Syndrome

“…The most common type of neuroimaging studied has been cranial CT. Cranial CT studies can show widespread injury to the brain with changes in edema characteristics. 61,305 The acquisition of magnetic resonance imaging studies is challenging in critically ill patients because of restrictions on the type of equipment that can be placed in the room; however, this is becoming less problematic, and magnetic resonance imaging studies in the critically ill are increasingly being undertaken. Some limited studies have shown that diffuse cortical abnormalities in diffusion-weighted imaging or fluid-attenuated inversion recovery are associated with poor outcome.…”

An Update in Postcardiac Arrest Management and Prognosis in the Era of Therapeutic Hypothermia

“…56 In a study of 25 comatose patients following CA for whom a CT scan was obtained within 48 hours, a difference in the gray matter to white matter ratio of <1.18 Hounsfield units at the level of the basal ganglia was predictive of death (0% FPR in 12 patients but with a wide confidence interval of 0%-22%). 57 Also, similar studies have had a low interrater reliability. 58 Brain MRI is frequently unremarkable despite other abnormal prognostic variables.…”