Time Course of Lung Changes at Chest CT during Recovery from Coronavirus Disease 2019 (COVID-19)

Abstract

Background Chest CT is used to assess the severity of lung involvement in coronavirus disease 2019 (COVID-19). Purpose To determine the changes in chest CT findings associated with COVID-19 from initial diagnosis until patient recovery. Materials and Methods This retrospective review included patients with real-time polymerase chain reaction-confirmed COVID-19 who presented between January 12, 2020, and February 6, 2020. Patients with severe respiratory distress and/or oxygen requirement at any time during the disease course were excluded. Repeat chest CT was performed at approximately 4-day intervals. Each of the five lung lobes was visually scored on a scale of 0 to 5, with 0 indicating no involvement and 5 indicating more than 75% involvement. The total CT score was determined as the sum of lung involvement, ranging from 0 (no involvement) to 25 (maximum involvement). Results Twenty-one patients (six men and 15 women aged 25-63 years) with confirmed COVID-19 were evaluated. A total of 82 chest CT scans were obtained in these patients, with a mean interval (±standard deviation) of 4 days ± 1 (range, 1-8 days). All patients were discharged after a mean hospitalization period of 17 days ± 4 (range, 11-26 days). Maximum lung involved peaked at approximately 10 days (with a calculated total CT score of 6) from the onset of initial symptoms (R² = 0.25, P < .001). Based on quartiles of chest CT scans from day 0 to day 26 involvement, four stages of lung CT findings were defined. CT scans obtained in stage 1 (0-4 days) showed ground-glass opacities (18 of 24 scans [75%]), with a mean total CT score of 2 ± 2; scans obtained in stage 2 (5-8 days) showed an increase in both the crazy-paving pattern (nine of 17 scans [53%]) and total CT score (mean, 6 ± 4; P = .002); scans obtained in stage 3 (9-13 days) showed consolidation (19 of 21 scans [91%]) and a peak in the total CT score (mean, 7 ± 4); and scans obtained in stage 4 (≥14 days) showed gradual resolution of consolidation (15 of 20 scans [75%]) and a decrease in the total CT score (mean, 6 ± 4) without crazy-paving pattern. Conclusion In patients recovering from coronavirus disease 2019 (without severe respiratory distress during the disease course), lung abnormalities on chest CT scans showed greatest severity approximately 10 days after initial onset of symptoms. © RSNA, 2020.

Figure 1:

Timeline of the pulmonary CT scans. d=days.

Figure 2:

Chest CT findings of COVID-19 pneumonia on transaxial images. (a) GGO; (b) crazy-paving pattern (GGO with superimposed inter- and intralobular septal thickening); (c) Consolidation. All images have the same window level of -600 and window width of 1600.

Figure 3:

Change in lung involvement on chest CT from time of onset of initial symptoms (in days). (a) The dynamic changes in total CT score for each patient; (b) Peak total CT lung involvement occurred at day 10 (curve fitting equation: y=0.001*x³-0.083*x²+1.329x+0.373, in which x = time from the onset of the initial symptoms, y = total CT score of the pulmonary involvement; R²=0.25, p<0.001). Quartiles of patients between 0 and 26 days are shown as stages 1 to 4.

Figure 4:

Changes in the proportions of patients with GGO, crazy praving pattern and consolidation as a function of stage (stage definitions from Figure 3).

Figure 5:

Typical evolution of CT findings in a47-year-old female patient presenting with persistent fever (38.8°C) for three days. (a) At presentation (day 3), a small region of subpleural GGO with partial consolidation was demonstrated in the right lower lobe; (b) day 7, there was an enlarged region of GGO with superimposed inter-and intralobular septal thickening (crazy-paving pattern) with partial consolidation; (c) day 11, partial resolution of the initial GGO, with a new area of subpleural consolidation; (d) day 20, continued resolution with minimal residual GGO and parenchymal bands were observed. All images have the same window level of -600 and window width of 1600.