COVID-19 pneumonia tends to worsen between one and two weeks of symptom onset, so carefully timed imaging helps physicians monitor patient status and predict the need for oxygen and ventilation, according to French thoracic imaging specialist Prof. Antoine Khalil. He offers six tips to beat the virus.
Most importantly, patients should not be imaged unnecessarily as this can expose technicians and other staff to contamination, he told viewers during the recent European Society of Cardiology (ESC) webinar, "Diagnostic imaging in COVID-19: chest x-ray and CT."
Patients may have pathologies other than COVID-19, says Prof. Antoine Khalil.Khalil, who is head of radiology at Hôpital Bichat-Claude Bernard in Paris and president of the French Society of Thoracic Imaging, gave these tips:
- Don't image if a patient is not hospitalized or does not need oxygen -- unnecessary imaging creates a major risk for technicians and other medical or nonmedical staff.
- If CT is available, opt for CT over x-ray as a one-shot solution -- again, this limits the risk to staff.
- The typical appearance of COVID pneumonia is ground-glass opacities or peripheral consolidation on chest x-ray and CT.
- CT is accurate. Trust typical CT findings, even if the polymerase chain reaction (PCR) test is negative, and consider repeating the PCR.
- Repeating CT around day 7 can predict the clinical course if a previous CT is available.
- Don't forget that patients may have pathologies other than COVID-19.
Cardiac imaging guru Dr. Stephan Achenbach, who moderated the ESC webinar, noted that while PCR is still the initial screening test for patients, imaging is used when symptoms are present. For sick patients, a CT result highly evocative of COVID-19 means that patients can be sent directly to the hospital without waiting for the PCR result.
Imaging is a good predictor of clinical course, noted Achenbach, chair of the department of cardiology at Friedrich-Alexander-Universität Erlangen-Nürnberg in Germany. Evolution is frequent in COVID-19 patients, and a worsening of lung abnormalities can predict that a patient's condition is deteriorating.
Khalil agreed, adding that "the extent of parenchymal lesions correlates with oxygen requirements. This extent also predicts the evolution towards resuscitation and mechanical ventilation."
For example, a patient with visible ground-glass opacities on CT or x-ray and who requires no oxygen at day 3 may show an extension of ground-glass opacities and require oxygen by day 9. By day 13, the patient could have respiratory distress and need to be hospitalized.
Khalil advocated performing CT at day 7 and again at day 15, depending on when patients presented with symptoms and their first examination. Further CT scans should be performed according to their clinical evolution and need for oxygen, he noted.
Check for pulmonary embolism
Achenbach reiterated that any clinical change should prompt another CT scan, particularly to check for pulmonary embolism.
He asked Khalil if radiologists should perform CT for a COVID-19 diagnosis or if the patient needed to wait for the results of the PCR test.
Dr. Stephan Achenbach from Erlangen.Khalil replied that in France, CT is not to be used for screening, but in the emergency department PCR results can take 24 hours. If a CT scan is evocative of diagnosis for an ill patient, that individual is sent to a COVID-19 bed without waiting for the results of the PCR test. If the PCR test is negative from a patient with positive CT results, the hospital repeats the PCR test, he noted.
However, his department does not CT screen patients who don't need oxygen or who don't need to be admitted to hospital. This strategy attempts to preserve medical and other staff from exposure to the virus. He also explained that the department opted for CT over x-ray whenever possible for the same reason; CT was most likely to provide answers immediately, whereas x-ray, particularly before day 5 of symptom onset, may be inconclusive and necessitate yet more imaging.
Bilateral peripheral consolidation or ground-glass opacities peak at 10 to 12 days from symptom onset, while chest x-ray findings have a lower sensitivity than initial PCR testing (69% versus 91%), according to Khalil, who echoed Achenbach's point that patients can be symptomatic with the disease and their chest x-ray can still be free of any typical signs.
Khalil pointed to the important differentials such as tuberculosis (TB) and bacterial pneumonia. He reminded radiologists and physicians that one pathology need not preclude another: It is possible for a patient to have both TB and COVID-19.
In addition, radiologists should remember that patients with heart failure and acute pulmonary edema may be infected with COVID-19, and two possible mechanisms behind imaging features are heart failure secondary to fever and dehydration and heart failure secondary to COVID-19 myocarditis.
At Hôpital Bichat-Claude Bernard, there is a "general diagnostic flow," he said. Every patient with fever, or a cough, and with peripheral or bilateral glass opacification with or without consolidation at CT, crazy-paving pattern, or reverse halo sign is suspected of having COVID-19 and is sent to a dedicated bed.
For emergency department patients, CT is preferred to x-ray in an attempt to limit staff exposure, unless it is dangerous to move the patient. Conversely, for nontransportable intensive-care patients, chest x-ray is preferred, except if there are complications or the symptoms are not explained by x-ray.
CT protocols include a first unenhanced low-dose CT sufficient to diagnose and see disease extent. In the case of sudden worsening of symptoms, angio-CT could be used to spot any pulmonary embolism, Khalil concluded.
Watch the webinar on the ESC website.
