Association between a quantitative CT scan measure of brain edema and outcome after cardiac arrest

Abstract

Background: Cerebral edema is one physical change associated with brain injury and decreased survival after cardiac arrest. Edema appears on computed tomography (CT) scan of the brain as decreased X-ray attenuation by gray matter. This study tested whether the gray matter attenuation to white matter attenuation ratio (GWR) was associated with survival and functional recovery.

Methods: Subjects were patients hospitalized after cardiac arrest at a single institution between 1/1/2005 and 7/30/2010. Subjects were included if they had non-traumatic cardiac arrest and a non-contrast CT scan within 24h after cardiac arrest. Attenuation (Hounsfield Units) was measured in gray matter (caudate nucleus, putamen, thalamus, and cortex) and in white matter (internal capsule, corpus callosum and centrum semiovale). The GWR was calculated for basal ganglia and cerebrum. Outcomes included survival and functional status at hospital discharge.

Results: For 680 patients, 258 CT scans were available, but 18 were excluded because of hemorrhage (10), intravenous contrast (3) or technical artifact (5), leaving 240 CT scans for analysis. Lower GWR values were associated with lower initial Glasgow Coma Scale motor score. Overall survival was 36%, but decreased with decreasing GWR. The average of basal ganglia and cerebrum GWR provided the best discrimination. Only 2/58 subjects with average GWR<1.20 survived and both were treated with hypothermia. The association of GWR with functional outcome was completely explained by mortality when GWR<1.20.

Conclusions: Subjects with severe cerebral edema, defined by GWR<1.20, have very low survival with conventional care, including hypothermia. GWR estimates pre-treatment likelihood of survival after cardiac arrest.

Figure 1

Subjects included in the study.

Figure 2

Average GWR decreases with initial GCS-motor score. Subjects with the lowest GWR had GCS-motor scores = 1.

Figure 3

Average GWR on initial CT scan is related to functional outcome at hospital discharge measured by a) Cerebral Performance Category and b) Modified Rankin Scale. Lower GWR was associated with CPC and mRS, but this association results from the fact that subjects with lower GWR died (CPC=5, mRS=6).

Figure 4

Mortality increases in subjects with lower average GWR receiving hypothermia (top) and patients not receiving hypothermia (bottom).