CT Scan comparison of COVID-19 versus Influenza virus pneumonia
COVID-19, an infectious respiratory disease caused by the novel coronavirus has changed the overall face of science and the medical world. Ever since the spread of coronavirus in 2019, questions have been arising about the symptoms that differentiate COVID-19 from flu or other diseases that could cause a respiratory tract infection. Clinically, COVID-19 shows symptoms that are similar to the influenza virus infection. However, the CDC 2019 released its update on COVID-19 symptoms and how to differentiate it from flu. The best way to determine if you have COVID-19 or flu is by testing and by undergoing a detailed examination that may include a CT (computerized tomography) scan.
Influenza pneumonia has been studied to have a similar pattern of infection, symptoms, and lung image findings to COVID-19. COVID- 19 and influenza can both affect your lungs that may cause a variation from the normal findings on a CT scan of the chest.
What does a CT scan tell you about the illness?
A CT scan of the chest essentially examines the health of your lungs and sometimes the heart. This is achieved by examining the blood flow throughout the lungs, the presence of any obstruction in the blood vessels of the lungs that could have been caused by the infection, pulmonary embolism (presence of air entrapment in lungs), and certain heart problems.
CT in COVID- 19
CT scan of a COVID-19 patient showing ground-glass opacities, Kwee et al, 2020
Chest CT is one of the diagnostic methods for COVID-19, however, several studies reported controversial results on considering CT as a precise way to diagnose COVID-19. Some studies reported that more than 60% of the patients with COVID 19 show lung changes in CT. Common findings in the CT of a COVID-19 patient may include ground-glass opacities (hazy gray areas visualized in a CT scan of lungs), vascular enlargement (increase in the size of the blood vessels of lungs), bilateral abnormalities (abnormal changes seen on both sides), and lower segment involvement of the lungs.2
These changes are mostly seen in symptomatic patients with severe COVID-19 disease.
Septal thickening (increase in the lung wall thickness), pleural thickening (thickening of the outer most layer of lungs), bronchial wall thickening (thickening of the lining of airway) are the other CT findings that are less commonly seen in COVID-19 patients.2
CT in Influenza virus Pneumonia
Since both COVID-19 and Influenza infections are respiratory illnesses that cause inflammation of the respiratory epithelium (cells of the airway), they both share similar characteristics in terms of signs and symptoms. Ground glass opacities are known to be present in influenza-associated pneumonia but commonly seen in the upper lobe whereas, in COVID-19, findings are common in the lower lobe. Other findings such as pleural effusion (“water on the lungs”), pure consolidation (the presence of pus or other cells in the airways and alveoli of lungs) are seen in influenza-associated pneumonia.3,4
Chest imaging, especially chest CT examination, is not often performed for the diagnosis and treatment of patients with influenza infection unless the patient has clinically gone into pneumonia. Moreover, CT findings of COVID-19 and influenza-associated pneumonia can overlap. Extensive research is happening around the use of CT in COVID-19. A team that includes a pulmonologist and a radiologist would study the images in detail to reach an accurate diagnosis of the condition after correlating the clinical findings with the CT image findings.