NHS England and NHS Improvement have produced clinical guide for the management of Radiology patients during the coronavirus pandemic. Link.
The Royal College of Radiologists
The Royal College of Radiologists has collected guidance and resources specific to the radiology community. Resources include Guidance for pre-operative chest CT imaging for elective cancer surgery during the COVID-19 pandemic, PPE advice, the role of CT in patients suspected with COVID-19 infection, and advice on non-urgent and cancer imaging during the coronavirus pandemic. Link.
Webinar from the Royal College of Radiologists entitled ‘Clarity on COVID-19 – a practical guide from the BSTI’. It is free as a recording for all RCR members. Link.
BIR – British Institute of Radiology
Links to resources from the British Institute of Radiology including guidance, webinars and podcasts. Link.
RSNA – The Radiological Society of North America
An editorial in the RSNA outlining essential information and updates for radiologists on COVID-19. Link.
A page from ‘Radiopaedia’ outlining the history of the COVID-19 outbreak and radiographic features associated with the disease. Link.
A video on the Imaging findings of COVID-19 from Stanford University. Link.
Health Education England
Radiology in COVID by HEE. Link.
A page on COVID-19 and the CT chest and chest radiograph findings of the disease. Link.
CHEST X RAY FINDINGS
In many countries, Chest X-Ray is the first line imaging modality for patients with suspected COVID-19. It is important to realise the Chest X-Ray can be normal, especially in early or non-severe disease. In a study of hospitalised patients with confirmed COVID-19 in China, 56% of patients with non-severe disease had a normal Chest X-Ray1.
When abnormal, the most common Chest X-Ray finding2 is bilateral consolidation which is typically:
- Worse in the lower zones
This X-Ray shows the typical features of COVID-19 pneumonia in a patient with positive PCR. There is bilateral consolidation worse in the periphery of the lung and predominantly seen within the lower zones. Here there is also involvement here of the left mid zone and right upper zone.
This X-Ray pattern has been described as the ‘reverse bat wing’ appearance, so-called as it is the opposite of the ‘bat wing’ appearance seen classically in pulmonary oedema where there is central rather than peripheral consolidation. Other than COVID-19 pneumonia, the ‘reverse bat wing’ has a differential diagnosis including eosinophilic pneumonia, organising pneumonia and pulmonary infarction.
In some patients the consolidation can be unilateral on admission to hospital – in a study of 64 hospitalised patients2, 38% of patients presented with unilateral consolidation with 63% presenting with bilateral consolidation.
Patients with unilateral consolidation on Chest X-Ray can progress on to having bilateral consolidation. Let’s have a look at another case of COVID-19 pneumonia confirmed with PCR.
On this X-ray there is consolidation within the left lower lobe. Note the patchy opacity within the peripheral left lower zone which obscures the left hemidiaphragm. As the left hemidiaphragm is not clearly seen the pathology can be localised to the left lower lobe (loss of silhouette sign). On this film the right lung is clear.
After 4 days we can see things have progressed. The extent of the left lower zone opacity has increased whilst there is new consolidation within the right mid zone, ie there is now bilateral consolidation. The bilateral consolidation is commonly symmetrical but can be asymmetrical as is the case here.
There are features on Chest X-ray that make COVID-19 less likely. These features have only been reported in a small number of COVID-19 cases and suggest bacterial superinfection or another diagnosis:
- Pleural effusion
- Tiny nodules
Significant mediastinal node enlargement
- Most patients with COVID-19 requiring hospital admission will show bilateral consolidation on their admitting Chest X-Ray
- The X-Ray can be normal in early or non-severe disease
CHEST CT FOR COVID-19
RT-PCR is the current gold standard for diagnosis of COVID-19. Although it is strong when it comes to specificity, there are issues with sensitivity and turn-around time for results.
In some parts of the world CT has been heralded as a quicker alternative however there are marked differences across the world in the use of CT to diagnose COVID-19. In the US and much of Europe, CT is not used as a first line tool given issues with lack of specificity and the potential to contaminate the CT scanner and staff. Although CT findings can be suggestive, the findings overlap with other viral pneumonias and non infective pathology.
There is some controversy regarding the true sensitivity of CT to pick up COVID-19. There is large variability in the literature, with sensitivity described anywhere between 61%3 and over 97%1,4.
The performance of CT in confidently diagnosing COVID-19 depends on several factors including:
- Prevalence of COVID-19 in the surrounding area: specificity increases with increasing prevalence – it is easier to call with some certainty that peripheral groundglass opacity is due to COVID-19 if there is a high burden of disease in the surrounding population
- Whether the patient is symptomatic or asymptomatic: a study of 104 patients with confirmed COVID-19 from the Diamond Princess cruise ship3 found sensitivity to be 54% for asymptomatic patients and 79% for symptomatic patients
- If symptomatic whether the disease is severe or non-severe: a study5 that included 975 hospitalised patients with confirmed COVID-19 who underwent CT found a sensitivity of 84% in non-severe disease and 95% in severe disease
This means the findings on chest CT cannot be taken alone and the patient history and surrounding prevalence of disease needs to be taken into account.
In terms of CT protocol, a non contrast scan is favoured as subtle regions of ground-glass opacity are better assessed (post contrast scans can give the appearance of false groundglass opacity). If a CTPA is needed to exclude pulmonary embolism one can consider performing a non contrast CT before hand to better assess the lung parenchyma5.
CHEST CT FINDINGS
The findings on CT vary according to when in the disease we image the patient6. Let’s look at the different findings we may encounter:
It is important to realise that chest CT may be normal in patients with COVID-19, especially in patients who are asymptomatic3 or have early (first 48 hours) or non-severe disease.
The key point here is that a normal CT does not exclude infection with COVID-19.
2. Ground-glass opacity
The typical finding on CT is of bilateral, peripheral, lower lobe predominant ground-glass opacity.
What is ground-glass opacity on CT? Ground-glass opacity refers to an increase of attenuation that does not obscure the underlying vessels on non contrast CT7 – this is usually caused by PARTIAL filling of the airspaces or thickening of the interstitium. Compare this with consolidation which refers to an increase in attenuation which does obscure the vessels, usually caused by COMPLETE filling of the airspaces and may be associated with an air bronchogram.
When CT is abnormal, ground-glass opacity is the most common finding and can be seen at all stages of disease9. Let’s have a look at this next image which shows some of the classic features:
There is bilateral peripheral ground-glass opacity – have a look at this region of ground-glass opacity within the left lung (yellow arrow). There is an increase in attenuation which does not obscure the vessels so we can call this ground-glass opacity. Furthermore you could draw around this region with a pencil, this is what we refer to as ‘geographic’ and is something that can be seen commonly with COVID-19.
When CT is abnormal, ground-glass opacity is commonly the first abnormality seen on CT and can worsen over time – in this next case the patient was imaged early on in disease (first 4 days) with the finding of upper lobe predominant ground-glass opacity. 8 days later a repeat CT shows diffuse peripheral geographic ground-glass opacity.
3. ‘Crazy paving’
The ‘crazy paving’ appearance refers to the presence of interlobular septal thickening within ground-glass opacity giving the appearance of irregularly shaped paving stones. Like the finding of ground-glass opacity, this is a non-specific finding but ‘crazy-paving’ appears to become more prevalent at the ‘peak stage’, 9-13 days after symptom onset6.
In this following case we can see areas of ‘crazy-paving’ within the right lung – look for the septal thickening within the regions of ground-glass opacity. This image is taken between 9-13 days after symptom onset.
Ground-glass opacity can progress to consolidation which again is typically peripheral and has a lower lobe predominance.
In this case there is peripheral consolidation within the right lung. The consolidation can show features of an ‘organising pneumonia’ that we can see in the case below:
Much like Chest X-Ray, there are features on CT that make COVID-19 less likely. These features have only been reported in a smaller number of COVID-19 cases and suggest bacterial superinfection or another diagnosis:
- Pleural effusion
- Tiny nodules
- Significant mediastinal node enlargement
- CT is not completely sensitive for diagnosing COVID-19 – a normal CT does not exclude COVID-19
- CT findings are not specific and prevalence in the surrounding area and the patient’s history and contact information must be taken into account.
- When abnormal, ground-glass opacity is the most common abnormality and is typically peripheral and lower lobe predominant.
- Findings can progress to ‘crazy-paving’, consolidation and features of an organising pneumonia namely bronchocentric consolidation and ‘lobular sparing’.
Guidelines and Recommendations
American College of Radiology (March 22 2020)
- CT should not be used to screen for or as a first-line test to diagnose COVID-19
- CT should be used sparingly and reserved for hospitalized, symptomatic patients with specific clinical indications for CT. Appropriate infection control procedures should be followed before scanning subsequent patients.
- Facilities may consider deploying portable radiography units in ambulatory care facilities for use when CXRs are considered medically necessary. The surfaces of these machines can be easily cleaned, avoiding the need to bring patients into radiography rooms.
- Radiologists should familiarize themselves with the CT appearance of COVID-19 infection in order to be able to identify findings consistent with infection in patients imaged for other reasons.
- (Updated March 22, 2020) As an interim measure, until more widespread COVID-19 testing is available, some medical practices are requesting chest CT to inform decisions on whether to test a patient for COVID-19, admit a patient or provide other treatment. The ACR strongly urges caution in taking this approach. A normal chest CT does not mean a person does not have COVID-19 infection – and an abnormal CT is not specific for COVID-19 diagnosis. A normal CT should not dissuade a patient from being quarantined or provided other clinically indicated treatment when otherwise medically appropriate. Clearly, locally constrained resources may be a factor in such decision making. Link.
Royal College of Radiologists (United Kingdom) (March 12 2020)
RCR position on the role of CT in patients suspected with COVID-19 infection
As coronavirus infections become identified increasingly worldwide and the number of cases increase in the UK, we have received a number of queries about the use of computed tomography (CT) scanning in the diagnosis of patients with possible COVID-19 infection. Reports from other countries with greater disease prevalence state that CT has been used as a diagnostic tool, particularly where access to viral testing kits is or becomes limited.
As of 12 March 2020, our view is that there is no current role for CT in the diagnostic assessment of patients with suspected coronavirus infection in the UK. We do not believe that current evidence demonstrates a clear benefit in producing a definitive and positive management change on the basis of CT information.
CT does have a well-established role in the assessment of patients presenting with severe respiratory distress, particularly those that deteriorate clinically, based on specific advice from – and discussion with – intensive care and respiratory teams. This clinical assessment of the need for cross-sectional imaging will remain and while these requests may increase with increasing numbers of patients presenting with severe respiratory illness, we do not believe that patients with known or suspected coronavirus infection should be imaged any differently. The CT request should be based on clinical need and subsequent likely change to the clinical management plan.
There are a number of publications presenting the CT chest imaging appearances of patients with coronavirus infection and links to some of these will be provided in the forthcoming resources section of the website. It is important for radiologists to familiarise themselves with the recognised imaging appearances as some patients not suspected of having coronavirus infection will undergo CT chest for other reasons. It is important to stress however that these imaging appearances are generally non-specific and overlap with the appearances of other viral chest infections including influenza, MERS and SARS. The CT appearances alone will not obviate the need for viral testing and should not be viewed as equivalent to or replacing this. Link.
Fleischner Society Statement (USA)
Summary of Recommendations
- Imaging is not routinely indicated as a screening test for COVID-19 in asymptomatic individuals
- Imaging is not indicated for patients with mild features of COVID-19 unless they are at risk for disease progression (Scenario 1)
- Imaging is indicated for patients with moderate to severe features of COVID-19 regardless of COVID-19 test results (Scenarios 2 and 3)
- Imaging is indicated for patients with COVID-19 and evidence of worsening respiratory status (Scenarios 1, 2 and 3)
- In a resource constrained environment where access to CT is limited, CXR may be preferred for patients with COVID-19 unless features of respiratory worsening warrant the use of CT (Scenarios 2 and 3)
- Daily CXR not indicated in stable intubated patients with COVID-19
- CT is indicated in patients with functional impairment and/or hypoxia after recovery from COVID-19
- COVID-19 testing is indicated in patients incidentally found to have findings suggestive of COVID-19 on a CT scan
British Society Thoracic Imaging guidance (United Kingdom)
Statement 11 March 2020
The coronavirus outbreak has now been labelled a pandemic by the World Health Organisation. It is highly likely that the number of cases in the UK will continue to rise substantially. This will put immense pressure on hospitals and intensive care units. While the use of real time reverse-transcription polymerase chain reaction (RT-PCR) from pharyngeal swabs remains the best diagnostic test for COVID-19, its availability and turnaround times will be similarly challenged. Focus has, therefore, in some commentaries turned to the use of computed tomography (CT). BSTI have been discussing this with NHS England. The current position is that there is no recommended use of CT, beyond ‘routine clinical care’. We are reassured that this has so far also been the position taken by the American College of Radiology, in recommendations published today. Link.
Link to imaging decision tool.
- Guan Z, Ni Z, Hu Y et al. Clinical Characteristics of Coronavirus Disease 2019 in China. N Engl J Med. 2020 Feb 28; DOI: 10.1056/NEJMoa2002032
- Wong HYF, Lam HYS, Fong AH et al. Frequency and Distribution of Chest Radiographic Findings in COVID-19 Positive Patients. (2019) Radiology.
- Inui S, Fujikawa A, Jitsu M, Kunishima N, Watanabe S, Suzuki Y et al. Chest CT Findings in Cases from the Cruise Ship “Diamond Princess” with Coronavirus Disease 2019 (COVID-19). Radiol Cardiothorac Imaging. 2020 Mar 17;2(2):e200110
- Ai T, Yang Z, Hou H, Zhan C, Chen C, Lv W et al. Correlation of Chest CT and RT-PCR Testing in Coronavirus Disease 2019 (COVID-19) in China: A Report of 1014 Cases. Radiology. 2020 Feb 26;200642
- Rodrigues, J.C.L. et al. An update on COVID-19 for the radiologist – A British society of Thoracic Imaging statement. (2020) Clinical Radiology.
- Pan F, Ye T, Sun P, Gui S, Liang B, Li L et al. Time Course of Lung Changes On Chest CT During Recovery From 2019 Novel Coronavirus (COVID-19) Pneumonia. (2020) Radiology
- Hansell DM, Bankier AA, MacMahon H, McLoud TC, Muller NL, Remy J. Fleischner Society: glossary of terms for thoracic imaging. Radiology. 2008 Mar;246(3):697-722.