Objectives:
COVID-19 infection demonstrates characteristic findings in chest CT. The optimal timing of repeated CT scans still needs to be clarified, and the optimal time to assess imaging clearance in COVID-19 is still unknown. It is crucial to have a roadmap of the imaging course of COVID-19 pneumonia to develop guidelines for prompt diagnosis of pulmonary complications, especially fibrosis, at the earliest stage.
Purpose: To assess the temporal changes of chest CT findings in patients with COVID-19 pneumonia and evaluate the rate of a complete resolution and determine the patients are at excessive risk for residual parenchymal abnormalities.
Materials and Methods: This retrospective observational study included 48 patients with real-time polymerase chain reaction–confirmed COVID-19 who were admitted to three academic hospitals. These patients underwent at least one initial chest CT before or after admission and at least one follow-up CT scan four weeks or more after the onset of the symptoms. All chest CTs were categorized according to time of performance into four groups, including the first week, second week, third-fourth week, and more than 28 days. Lung involvement was categorized as predominantly alveolar (ground-glass opacity and consolidation), organizing pneumonia, and reticular patterns. The severity of involvement was also evaluated by the reader.
Results: Forty-eight patients and a total of 130 chest CT scans were evaluated. The alveolar pattern showed a gradual decrease in frequency from 91% in the first week to 9% after the fourth week of the disease but the organizing pneumonia pattern gradually increased with disease progression and the frequency of reticular pattern increased significantly after third week. Complete resolution of CT findings was seen in 17 patients (13.1%) and was significantly more prevalent in patients of younger age (p value<0.001) and with lower initial CT severity scores (p value=0.048). CT severity scores in the second week were significantly higher in ICU admitted patients (p value=0.003).
Conclusion: There are temporal patterns of lung abnormalities in patients with COVID-19 pneumonia. The predominant CT pattern was alveolar infiltrate in the first and second weeks of the disease, replaced with an organizing pneumonia pattern in the third and fourth weeks. Progression of lung involvement was correlated with ICU admission due to the highest CT severity score in the second and third weeks of presentation but not in the first week in patients who were admitted at ICU. Complete CT resolution was significantly more common in patients of younger age and lower initial CT severity scores.