Abstract: Objective Diffusion weighted imaging (DWI)-negative acute ischemic stroke is not uncommon, but likely to cause difficulty to diagnose. The purpose of this study was to describe the clinical and imaging features of DWI-negative patients with acute ischemic stroke and discuss the potential causes. Methods We retrospectively selected DWI-negative patients with suspected acute ischemic stroke presented to the Code Stroke System of Beijing Tiantan Hospital, from January 2012 to July 2014. Data of demographic characteristics, clinical presentations and imaging were collected, and causeswere classified. Results 134 patients (90 men and 44 women) were included. Median age was 57 years (interquartile range 50~70). Median interval from the onset to DWI were 266.5 minutes (interquartile range 205.3~362.5). Median National Institutes of Health Stroke Scale (NIHSS) score 2 (interquartile range 1~3). 33 patients were hospitalized for further treatment. There are 27 cases (81.8%) diagnosed as ischemic stroke, 6 cases (18.2%) diagnosed as other diseases. Among the 27 patients with ischemic stroke, infarction leisions were found in 9 cases (33.3%) after the films were re- read, in 5 cases (18.5%) when DWI repeated after symptoms getting worse, in 1 case (3.7%) when DWI repeated without aggravating. Large vessel occlusion/stenosis on magnetic resonance angiography (MRA) or hypoperfusion on perfusion weighted imaging (PWI) responsible for symptoms were found in 1 case (3.7%) with aggravating, in 6 cases (22.2%) without aggravating. No infarction leision or large vascular abnormalities on MRA was found in 5 cases (18.5%). In 27 patients with ischemic stroke, based on Trial of Org 10172 in Acute Stroke Treatment (TOAST) classification criteria, 15 cases (55.6%) were attributed to large artery atherosclerosis, 11 cases (40.7%) were attributed to small artery occlusion, 1 case (3.7%) was attributed to unknown etiology. In 33 hospitalized patients, besides 1 case with disability, all the other 32 cases (97.0%) were discharged with good outcome. 101 patients were discharged after emergency treatment. Among them, infarction leisions were found in 5 cases (5.0%) after the films were re-read. Large vessel occlusion/stenosis on MRA or hypoperfusion on PWI responsible for symptoms were found in 14 cases (13.9%) and the diagnosis was modified as ischemic stroke. Another 2 patients (2.0%) were diagnosed as diseases other than cerebral infarction. No abnormality on imaging was found in the other 80 cases (79.2%). Conclusion DWI-negative acute ischemic strokes are mostly minor stroke. Large artery atherosclerotic occlusion/stenosis and small artery occlusion are the main cause. In the the Code Stroke System, DWI-negative patients with suspected acute ischemic stroke primarily interpreted by stroke doctors have a possibility of lesions omitted and imaging delayed, also the risk of aggravation.

Key words: Diffusion weighted imaging; Ischemic stroke; Large artery atherosclerosis; Small artery occlusion

摘要： 目的 探讨弥散加权成像 （diffusion weighted imaging， DWI） 阴性的急性缺血性卒中患者的临床特点、 影像学表现、 病因。 方法 回顾性分析自2012年1月～2014年7月首都医科大学附属北京天坛医院神经内科急诊溶栓绿色 通道就诊的DWI阴性的疑似急性缺血性卒中患者， 收集其人口学特征、 临床表现、 影像数据， 进行病 因学分类。 结果 连续收集134例溶栓医生初步判断为DWI阴性的疑似急性缺血性卒中患者， 其中男性90例， 女 性44例， 中位数年龄57岁 （四分位数间距50～70） ， 从发病到完成DWI检查的中位数时间266.5 min （四 分位数间距205.3～362.5） 。 中位数美国国立卫生研究院卒中量表 （National Institutes of Health Stroke Scale， NIHSS） 评分2 （四分位数间距1～3） 。 33例患者住院进一步诊治。 有27例 （81.8%） 被诊断为缺血 性卒中 ， 另有6例 （18.2%） 诊断为其他疾病。 27例诊断为缺血性卒中的住院患者中 ， 9例 （33.3%） 经 重新读片后发现缺血灶， 5例 （18.5%） 症状加重后复查出现缺血灶， 1例 （3.7%） 未加重但复查出现 缺血灶， 1例 （3.7%） 症状加重后复查DWI仍无缺血灶但有可以解释症状的磁共振血管成像 （magnetic resonance angiography， MRA） 大血管闭塞/狭窄或灌注加权成像 （perfusion weighted imaging） 低灌注 区， 6例 （22.2%） 虽DWI阴性但MRA有可以解释症状的大血管闭塞/狭窄或PWI有低灌注区， 5例 （18.5%） DWI阴性且未见大血管异常。 诊断为缺血性卒中的27例患者， 根据急性卒中治疗低分子肝素试验病 因分型法 （Trial of Org 10172 in Acute Stroke Treatment， TOAST） 的分型标准， 15例 （55.6%） 为大动 脉粥样硬化， 11例 （40.7%） 为小动脉闭塞， 1例 （3.7%） 病因不明。 住院患者中 ， 除1例 （3.0%） 患者出 院时明显残疾外， 其余32例 （97.0%） 患者出院时结局良好。 101例患者在急诊治疗后出院。 其中80例 （79.2%） DWI阴性且未见其他异常， 5例 （5.0%） 经重新读片后发现缺血灶， 14例 （13.9%） 虽DWI阴性但 MRA有可以解释症状的大血管闭塞/狭窄或PWI低灌注区修正诊断为缺血性卒中 ， 2例 （2.0%） 诊断为 其他疾病。 结论 DWI阴性的急性缺血性卒中 ， 多数为小卒中 。 大动脉粥样硬化性闭塞/狭窄和小动脉闭塞是主 要病因。 在急诊溶栓绿色通道中 ， 溶栓医生初步判断为DWI阴性的疑似急性缺血性卒中患者， 存在读 片遗漏、 显影延迟的可能和病情加重的风险。

关键词: 弥散加权成像; 缺血性卒中; 大动脉粥样硬化; 小动脉闭塞