Gray/White Matter Ratio as an Outcome Predictor for Cardiac Arrest Patients Treated by Therapeutic Hypothermia

Lim, Seong Wook; Lee, Byung Kook; Lee, Hyoung Youn; Jeung, Kyung Woon; Ryu, Hyun Ho; Chun, Byoeng Jo; Moon, Jeong Mi; Heo, Tag; Min, Yong Il

Abstract

PURPOSE
Ischemic brain injury following cardiac arrest presents as cerebral edema. Cerebral edema can be diagnosed using computed tomography (CT) by evidence of difference in the ratio between gray and white matter density. The prognostic value of CT scan use in determining neurologic outcomes remains unclear for cardiac arrest survivors treated with therapeutic hypothermia. We investigated the density of gray and white matter and found that their ratio was associated with neurologic outcome.
METHODS
Our study data included 93 cardiac arrest survivors treated with therapeutic hypothermia from January 2008 to June 2011. Cranial CT was performed after the return of spontaneous circulation. Circular regions of CT measurement (9.4 mm2) evaluated locations of interest including the caudate nucleus, putamen, posterior limb of the internal capsule, and the corpus callosum. The average attenuation in Hounsfield Units (HU) for each region was recorded. Neurological outcome was ranked as good or poor at discharge with neurological outcome assessed according to the Cerebral Performance Category scale (CPC) with a poor outcome defined as a CPC of 3-5.
RESULTS
Gray matter attenuation was found to be significantly different between the good and poor outcome cases while white matter attenuation was insignificant. All types of gray/white matter ratio were significantly different between two groups. Receiver operating characteristics analysis determined a cut-off value of gray/white matter ratio at less than 1.11 (sensitivity 29.8%) which results in a poor outcome with a specificity of 100%.
CONCLUSION
A low gray/white matter ratio (<1.11), as evaluated by CT scan, is associated with poor outcome after cardiac arrest and therapeutic hypothermia. However, the results of a CT scan should be interpreted with caution as the gray/white matter ratio is a low sensitivity marker.