撰稿：Authors: Daniel J Durand, MD;
Chair, Department of Radiology, LifeBridge Health System；
审稿：Rishi Desai, MD, MPH, Yifan Xiao, MD；
According to the WHO, as of March 6, 2020, so in just the first three months of the outbreak, there have been 100,685 cases of COVID-19 and 3,411 deaths, that works out to a mortality rate of 3.4%. On top of that, every case of COVID-19, leads to roughly 2.3 new cases, meaning that the outbreak is still spreading. Many countries have been affected, and there are numerous cases of community spread, meaning that individuals are getting sick without being around any sick contacts or having traveled to outbreak areas. In that context, healthcare workers need a diagnostic tool for COVID-19 that’s highly sensitive, in other words, a tool that allows them to catch almost every single case.
据WHO提供的数据，截至2020年3月6日，仅在疫情爆发的第三个月，COVID-19累计确诊已达 100,685 例，死亡 3,411 例，病死率 3.4%。最重要的是，每例COVID-19感染都会导致大约2.3例新病例的产生，这意味着疫情仍在蔓延。许多国家都受到疫情影响，其中很多病例为社区传播，即 他们并无疫情爆发地区旅行史，也无受感染者接触史。在这样的情况下，医疗工作者需要高度敏感的COVID-19诊断工具，做到尽量不漏诊每一个病例。
The gold standard for diagnosis of COVID-19 is RT-PCR, or reverse transcription polymerase chain reaction. But here’s the problem, current data suggest that RT-PCR is initially only 30-70% sensitive for acute infection. In other words, 3 to 7 out of 10 patients that actually have COVID-19 will have a negative PCR result. There could be many reasons for this, perhaps early in the disease, there’s not enough virus in the blood for detection, or perhaps the lab kits weren’t being correctly used.
However, the largest study to date of over 1000 patients showed chest CT has an initial sensitivity of over 95%, meaning that less than 1 out of 20 cases would get missed. That has massive implications because far fewer people with COVID-19 would get sent back home where they can get sicker, and spread the disease to others.
Now, the RT-PCR test may improve over time, but it’s clear that chest CT had higher sensitivity early on in the disease for patients sick enough to present to hospital settings in China. This strongly suggests that chest CT can be used to identify patients that need further testing, as well as for isolation and to help inform treatment. This is especially relevant in settings with good access to CT technology but poor access to reliable laboratory testing - or in situations where centralized public health laboratory tests have a turnaround of many hours or days.
Typically, when a patient has symptoms of COVID-19, like fever, cough, or shortness of breath, they may get a chest X-ray. Because they’re cheaper and easier to do than CTs, they’re often done first. The most common abnormal finding is “ground glass” opacities, meaning that some portions of the lungs look like a “hazy” shade of gray instead of being black with fine white lung markings for blood vessels. It looks a bit like frosted glass, like a window in the wintertime. It is important to note, however, that chest X-rays are not very sensitive for COVID-19 and that patients who are highly suspicious for COVID-19 viral pneumonia should probably get a chest CT even if their initial chest X-ray is negative.
通常，当某个患者出现COVID-19的症状，如发热、咳嗽、呼吸急促时，会先使用胸片检查。较CT而言，胸片的成本更低、且易操作，往往是首选的检测方法。最常见的胸片异常表现是磨玻璃影，意味着肺部某些部位有模糊的灰色阴影，而非呈现黑色背景下细小的白色肺纹理（即血管影），就像是在冬天结了霜的玻璃。需要注意的是，胸片 对 COVID-19 的敏感性不高；高度怀疑为 COVID-19（新型冠状病毒肺炎） 的病例，即使胸片检查结果为阴性，仍应进行胸部CT检测。
Now compared to chest X-rays, chest CT gives a much more detailed view. The most common CT finding in COVID-19 are those ground-glass opacities scattered throughout the lungs. They represent tiny air-sacs or alveoli getting filled with fluid, and turning a shade of grey on CT scans.
In severe or more advanced infections, more and more fluid will accumulate in the lobes of the lungs, so the ground glass appearance will progress to a solid white “consolidation.”
Finally, there’s a finding called the “crazy paving” pattern due to swelling of the interstitial space along the walls of the lung lobules. This makes the walls look thicker, like white lines against the hazy, ground glass background. The appearance is similar to irregularly-shaped stones used to pave a street, hence the name “crazy paving.”
These three CT findings - ground-glass opacities, consolidations, and crazy paving patterns, can be seen in isolation or in combination with one another. Ground-glass is usually the first sign and is followed later by one or both of the others.
磨玻璃影、肺实变 & 碎石路征 这三种CT改变可以单独或者合并出现。磨玻璃影一般是首发影像表现，另外两种体征随后单个或者同时出现。
These findings usually occur in multiple lobes throughout both lungs, and more commonly affect the outermost or periphery of the lungs. Having said that, in mild or recovering cases of COVID-19, the findings can be isolated to just one lobe.
It’s no surprise then, that disease severity is proportionate to the lung findings. The sickest individuals typically have the most severe findings on chest CT. And as patients improve, there’s gradual resolution of the ground glass and consolidations.
Now, it’s worth mentioning that there are some key CT findings that are typically absent in COVID-19.
You don’t usually see pleural effusions which are fluid collections in the pleural space right outside of the lungs. These are more common in conditions like congestive heart failure and bacterial pneumonia.
You also don’t see large lymph nodes in the mediastinum or near the hilum or central part of the lung, which are often seen in other types of pneumonia.
Finally, you don’t typically see lung cavities, which usually develop in bacterial and fungal pneumonia due to necrosis of the lung tissue later turning into an air-filled cavity.
胸腔积液，也就是在肺间隙有液体积聚，在COVID-19患者很少出现，而在充血性心力衰竭 & 细菌性肺炎等情况更常见。
Now, even though a chest CT is very sensitive for COVID-19, the key findings, ground-glass opacities, consolidations, and crazy paving, can also be seen with other causes of viral pneumonia, like influenza and adenovirus. They can also be seen in a variety of non-infectious conditions. That means that chest CT is sensitive, but not very specific for COVID-19, and that individuals with these findings should get thorough testing done. A number of countries have been isolating patients with classic CT findings until laboratory tests help identify the cause of the disease, and they can be properly treated.
虽然胸部CT对COVID-19的敏感性很高，但这些特征性改变——磨玻璃影、肺实变、碎石路征——也可以在其他病毒引起的肺炎中看到（如流感病毒、腺病毒），这些影像在一些非感染性疾病中也可以出现。 这意味着胸部CT敏感性虽然高，但对COVID-19并不是很特异，因此，对发现有这些影像表现的患者应进一步进行全面的检查。 在许多国家，通过实验室检查明确病因之前，都会隔离这些有典型CT表现的患者，这样可以帮助明确诊断，对其进行相应治疗。
Lastly, it’s important to recognize that the role of CT in evaluation patients will depend on the severity of infection in that patient, as well as the prevalence of COVID-19 in that community.
In individuals who are asymptomatic or have really mild disease, the sensitivity of chest CT falls to about 50% if it’s done in the first 48 hours of symptoms. In other words, individuals with very mild disease may eventually have positive RT-PCR results, but would have been missed by an early chest CT scan. Also, chest CT is less useful as a screening tool in areas where there’s very little circulating COVID-19, because the findings are more likely due to other causes.
对于无症状或症状轻微的患者，如果在发病的最初48小时进行胸部CT检查，其敏感性会下降到约50％。 换句话说，症状表现轻微的患者可能会出现病程后期的RT-PCR的阳性结果，但是病程早期的胸部CT扫描为阴性。 同时，因为其类似的影像表现很可能与其他病因有关，在目前COVID-19的低发区域，胸部CT并没有作为常规筛查的工具。
On the other hand, chest CT is most useful in patients who are acutely ill and symptomatic in areas with a high burden of COVID-19 disease - similar to the situation in the initial outbreak in China. In this scenario, patients with classic CT patterns of COVID-19 and no other explanation for these findings should be treated as presumptive infections even if their initial R-PCR test is negative.
胸部CT最适用于 目前COVID-19高发地区的 急性发病 & 症状明显 的患者筛查，也就是类似国内疫情爆发最初时的情况。 在这种情况下，即使病程早期的RT-PCR测试结果为阴性，但患者具有COVID-19的典型CT影像学表现，且对这些发现不能用其他原因解释，也应视为推定性感染，对其进行相应治疗。
The higher the prevalence is in a given area, the more likely it is that the highly sensitive but nonspecific CT findings represent a true case of COVID-19, that will eventually turn positive on RT-PCR.
So as a quick recap, in early COVID-19 disease chest CT showed a much higher sensitivity than RT-PCR for the initial stages of the disease in hospitalized patients, although this may change as the RT-PCR test is improved. The key findings on chest CT include ground-glass opacities, consolidations, and crazy paving. Individuals presenting to hospitals with these chest CT findings may need isolation and should get thorough confirmatory testing and appropriate treatment. Lastly, follow-up CT scans can help monitor disease progression and recovery.
简单总结回顾一下。对于COVID-19感染初期的住院患者，胸部CT表现出比RT-PCR更高的敏感性，而RT-PCR检测技术的改进可能改变这一现状。 胸部CT的典型表现包括磨玻璃影、肺实变 & 碎石路征。 来院时有这些胸部CT表现的患者可能需要被隔离，并接受进一步全面的检查和相应治疗。 后续跟进的CT扫描可以帮助监测疾病的进展和恢复情况。
～ 医番【17.2182.3】现身 ～
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