Review on radiological evolution of COVID-19 pneumonia using computed tomography

Table 1 Characteristics and findings of the studies included in the systematic review

Ref.	Type of study	Patients included	Mean age in yr, range	CT scan follow-up	CT evaluation, scoring system
Han et al[9], 2020	Retrospective	17 surviving and discharged patients with COVID-19 pneumonia	40 ± 6	4 wk (4 weekly CT scan during hospitalization)	Semi-quantitative
Wang et al[10], 2020	Retrospective	63 patients with asymptomatic/mild, 378 with moderate, 43 with severe/critically COVID-19 pneumonia	47 (33-57)	From symptoms onset to beyond day 15	Quantitative
Liang et al[11], 2020	Retrospective	88 patients with mild COVID-19 pneumonia	42.7 (4-82)	3 wk after disease onset	Semi-quantitative
Sun et al[23], 2021	Case series	11 patients with severe COVID-19 pneumonia	52 (33-75)	CT scan during hospitalization (not well defined, at least 3 wk during hospitalization)	Qualitative
Zhou et al[12], 2020	Retrospective	100 patients with COVID-19 pneumonia (without ARDS)	52.3 ± 13.1 (27-80)	CT during hospitalization (from symptoms onset to beyond day 21)	Semi-quantitative
Wang et al[13], 2020	Retrospective	126 patients with COVID-19 pneumonia, (severe and critical cases excluded)	41.2 ± 10.8	CT scan during hospitalization (mean days of hospitalization 22 ± 5 d (12-40)	Qualitative
Wang et al[14], 2020	Retrospective	79 patients with non-severe (mild/common) COVID-19 pneumonia, 27 with severe pneumonia	48.0 ± 15.4	CT scan during hospitalization (mean days of hospitalization 25) + CT scan at 2-4 wk after discharge	Semi-quantitative
Zhang et al[15], 2020	Retrospective	33 patients with moderate COVID-19 pneumonia	49.0 ± 15.5	CT scan during hospitalization (mean days of hospitalization 20.8, range 18-37)	Semi-quantitative
Feng et al[16], 2020	Retrospective	19 patients with COVID-19 pneumonia	43.6 ± 15.5 (10-67)	0-34 d after symptoms onset	Quantitative
Liu et al[17], 2020	Retrospective	149 discharged patients with COVID-19 pneumonia (142 pneumonia, 7 severe pneumonia, no critical patients included)	43 (36-56)	Basal CT scan at discharge and at 1st, 2nd and 3rd week after discharge	Semi-quantitative
Pan et al[18], 2020	Retrospective	105 patients with COVID-19 pneumonia (severe pneumonia excluded)	48.6 ± 13.1 (23-72)	1-47 d after symptoms onset	Semi-quantitative
Zhuang et al[19], 2021	Retrospective	22 patients with COVID-19 pneumonia with solitary pulmonary lesion	40.7 ± 10.3 (23-54)	CT scan during hospitalization (mean days of hospitalization 19 d, range: 11-44) + first CT scan after discharge	Semi-quantitative
Urciuoli and Guerriero[24], 2020	Case series	6 patients with mild COVID-19 pneumonia	59.5	First CT on admission and 4 mo after symptoms onset	Qualitative
Zhang et al[20], 2020	Retrospective	53 patients with common COVID-19 pneumonia, 20 patients with severe COVID-19 pneumonia	45 ± 14 common pneumonia, 50 ± 15 severe pneumonia	0-30 d after symptoms onset	Quantitative
Pan et al[21], 2020	Retrospective	21 patients with COVID-19 pneumonia (severe pneumonia excluded)	40 ± 9 (25-63)	0-26 d after symptoms onset	Semi-quantitative
Wang et al[22], 2020	Prospective	90 patients with COVID-19 pneumonia	45 ± 14 (5-43)	0-24 d after symptoms onset	Semi-quantitative

ARDS: Acute respiratory distress syndrome; COVID-19: Coronavirus disease 2019; CT: Computed tomography.

Table 2 Computed tomography scan features of lung lesions according to the follow-up timing of coronavirus disease 2019 pneumonia

Ref.	Short-term follow-up, dynamic evolution during hospitalization period: Severity and timing	Main CT features at short-term follow-up	Late follow- up, dynamic evolution after hospital discharge	Main CT features at late follow- up
Han et al[9], 2020	Initial deterioration to a peak at the 2nd week followed by improvement in the 3rd and 4th week	GGO decreased from 1st week to 2nd week, then increased in 3 and 4. Consolidation and a mixed pattern noted in 2 wk. Crazy paving pattern had the highest frequency in 2nd week	N/A	N/A
Wang et al[10], 2020	Severe/critically ill group: Opacity volume continued to increase beyond 15 d. Moderate group: Peak on days 13-15 (the opacity density began to drop from day 10 to day 12). Asymptomatic/mild group: Highest opacity volume on days 1-3 and almost resolved after 15 d	GGO in the early stages, followed by appearance of consolidations. In the severe/critically ill group: Decreasing trend of GGO, increasing trend of consolidation over time	N/A	N/A
Liang et al[11], 2020	Total severity score showed an increasing trend in the first 2 wk, followed by a slight decrease in the 3rd week	GGO was the most common finding over time, consolidation decreased 2 wk after symptom onset. Reticulations and linear opacities and fibrosis became increasing prevalent later in the disease course	N/A	N/A
Sun et al[23], 2021	Improvement in the first 3 wk after hospitalization	Decrease in consolidation and GGO overtime and appearance of fibrous-like stripes	N/A	N/A
Zhou et al[12], 2020	3 stages: Early rapid progressive stage (1-7 d from symptom onset); > advanced stage with peak levels of abnormalities on CT at 8-14 d; > improvement after 14 d (particularly, after 21 d the absorption was more obvious)	GGO, GGO + reticular pattern/consolidation in the rapid progressive stage. ↑ GGO + reticular pattern and consolidation in the advanced stage. ↓ GGO + reticular pattern and consolidation and ↑ subpleural line, bronchus distortion, and fibrotic strips in the absorption stage	N/A	N/A
Wang et al[13], 2020	3 stages: Progression process; > absorption process; > stage of discharge	↑ GGO with consolidation (↑ crazy paving pattern, ↑ vascular thickening sign ↑ air bronchogram sign) in the progression process. Absorption of consolidation displayed as inhomogeneous partial GGOs with fibrosis shadows, occurrence of the fishing net on trees sign, ↑ fibrosis sign, ↑ subpleural line sign in the absorption process. Further absorption of GGOs, consolidation and fibrosis shadows and no appearance of new lesions in the stage of discharge	N/A	N/A
Wang et al[14], 2020	Radiological aggravation (< 2 wk) and improvement (> 2 wk)	GGO decreased while mixed GGO and consolidation increased from 1 wk to 2 wk after onset; linear opacity increased from 2 wk to 3 wk after onset	1-2 mo after symptom onset (median day 38): In 1/3 of cases complete absorption of lesions. Patients with more severe lesions at day 8-14 (> consolidations, CT score > 4, > 3 lobes involved) were more prone to have pulmonary residuals	Mainly linear opacities
Zhang et al[15], 2020	4 stages: Early stage (0-5 d); > peak stage (6-10 d); > absorption stage (11-15 d); > recovery stage (≥ 16 d)	Mainly GGO, (vascular thickening, bronchial wall thickening, and consolidation were also noted) in the early stage. ↑ GGO, vascular and bronchial thickening, and consolidation (mean peak at 8 d) in the peak stage. GGO and consolidation were predominantly present, with ↑ bronchial wall thickening and vascular thickening in the absorption stage. GGO and consolidation were partially absorbed, and bronchial wall thickening and vascular thickening ↓ (residual GGO and subpleural parenchymal bands) in the recovery stage	N/A	N/A
Feng et al[16], 2020	3 stages: Progressive stage (0-5 d); > peak stage (5-15 d). The greatest severity showed approximately 7-8 d from onset; > absorption stage (15-30 d)	GGO and interlobular/intralobular septal thickening were the most frequent CT manifestation	N/A	N/A
Liu et al[17], 2020	N/A	N/A	At 3 wk follow up CT scan: Complete absorption of lesions in more than half of the patients	Gradually decrease of GGO and fibrous stripe (GGO during the first and fibrous stripe the 3rd week after discharge). “Tinted” sign and bronchovascular bundle distortion
Pan et al[18], 2020	5 stages: 0-3, 4-7, 8-14, 15-21, and > 21 d from symptoms onset (stages A-E, respectively). The total CT score of lung involvement was significantly higher in Stage C. The lung lesions in most patients improved after 14 d since initial symptom onset	Proportion of GGO was similar in each stage, consolidation gradually ↑ from Stage A to C and gradually ↓ from Stage C to E	N/A	N/A
Zhuang et al[19], 2021	Lung involvement peak at approximately 11 d, then lung lesions improved significantly	Mainly GGO in the first scan (0-4 d), crazy-paving pattern and consolidation in scan-2 (4-22 d), lesions were gradually absorbed and tended to be stable and linear opacities were noted in the scan-3 (before discharge, 6-41 d)	1st CT scan after discharge (22-51 d): Further absorption of lung lesions	Various presentations: negative CT scan, GGO, consolidation, linear opacities
Urciuoli and Guerriero[24], 2020	N/A	N/A	Persistence of lung abnormalities in 5/6 cases even if all the patients completely asymptomatic	Various presentations: 1 negative CT scan; in 2 patients, persistence of mixed pattern (GGO and fibrous streaks); in 1 patient fibrotic stripes, in 1 patient mixed pattern (interlobular septal thickening and patchy GGO); in 1 patient fibrotic pattern
Zhang et al[20], 2020	5 stages: Stage 1 (0-3 d), stage 2 (4-7 d), stage 3 (8-14 d), stage 4 (15-21 d), and stage 5 (22-30 d). PTV peaks at 12 d in common pneumonia, at 17 d in severe pneumonia	Common pneumonia: No significant differences in the PTV, PGV and PCV between stages 1-4 (percent of lesions was reduced in stage 5 compared with stage 4). Severe pneumonia PTV, PGV and PCV ↑ from stage 2 to stage 4 and ↓ in stage 5	N/A	N/A
Pan et al[21], 2020	4 stages: Early stage (0-4 d); progressive stage (5-8 d); peak stage (10-13 d); and absorption stage (≥ 14 d). Peak at 10 d after symptoms onset. CT signs improvement at approximately 14 d	GGO in the early stage, ↑ crazy-paving pattern and consolidation in the progressive stage, consolidation in the peak stage, progressive resolution of consolidation in the absorption stage	N/A	N/A
Wang et al[22], 2020	Lung abnormalities increased quickly after the onset of symptoms, peaked around 6-11 d, and were followed by persistence of high levels in extent for a long duration (slow absorption of the lesions)	GGOs trend: “first falling then rising”. Consolidation was the second most common feature seen in the first 11 d. Mixed pattern: The second most predominant pattern since illness days 12-17	N/A	N/A

CT: Computer tomography; GGO: Ground glass opacity; N/A: Not applicable; PCV: Percentage of consolidation volume; PGV: Percentage of ground glass opacity volume; PTV: Percentage of total lesion volume.