Torbey M T, Selim M, Knorr J, Bigelow C, Recht L
Department of Neurology, University of Massachusetts Medical School, Worcester 01655, USA.
Stroke. 2000 Sep;31(9):2163-7. doi: 10.1161/01.str.31.9.2163.
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.
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.
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 (P:<0.0001, 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 (P:=0. 035, 1-tailed t test). Using receiver operating characteristic curve analysis, we determined that a difference in GM/WM ratio of <1.18 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 >1.18. The empirical risk of death was 21.67 for comatose patients with a value below threshold.
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 <1.18 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.
轶事报道表明，根据CT扫描判断，昏迷患者脑灰质（GM）和白质（WM）之间的区分度丧失预示着心脏骤停后预后不良。为解决这一问题，我们对心脏骤停后昏迷患者不同脑区的GM和WM密度进行了定量评估。
通过追踪我院神经科会诊情况的计算机数据库，确定在心脏骤停后24小时内被要求会诊的患者。确定了25例昏迷患者，其完整的病历和CT扫描可供查阅。25例CT扫描结果正常的连续患者作为对照。从基底节、半卵圆中心和高凸面区域水平的轴向图像中获取的小定义区域测量亨氏单位（HU）。
在每个测试水平上，与正常对照组相比，昏迷患者的GM密度较低，WM密度较高。昏迷患者的GM/WM比值显著低于对照组（P<0.0001，秩和检验）。对照组和研究组患者的GM/WM比值基本没有重叠。差异在基底节水平最大。我们还观察到心脏骤停死亡患者和存活患者在基底节水平的GM/WM比值存在边缘显著差异（P=0.035，单尾t检验）。使用受试者工作特征曲线分析，我们确定基底节水平GM/WM比值<1.18可100%预测死亡。在基底节水平，该阈值以下的12例患者无一存活，而比值>1.18的患者存活率为46%。低于阈值的昏迷患者的经验性死亡风险为21.67。
GM与WM的HU比值提供了一种可重复的灰质和白质区分度测量方法。心脏骤停后立即昏迷的患者GM/WM比值较低。基底节水平似乎是CT上测量这种关系最敏感的部位。尽管在这项回顾性研究中，该水平GM/WM比值<1.18可预测死亡，但本研究中的差异不够显著，不足以推荐根据CT结果做出管理决策。然而，这些结果确实值得考虑进行前瞻性研究，以确定CT扫描在预测心脏骤停后昏迷患者预后方面的可靠性。
