Chest CT score in COVID-19 patients: correlation with disease severity and short-term prognosis

Abstract

Objectives: To correlate a CT-based semi-quantitative score of pulmonary involvement in COVID-19 pneumonia with clinical staging of disease and laboratory findings. We also aimed to investigate whether CT findings may be predictive of patients' outcome.

Methods: From March 6 to March 22, 2020, 130 symptomatic SARS-CoV-2 patients were enrolled for this single-center analysis and chest CT examinations were retrospectively evaluated. A semi-quantitative CT score was calculated based on the extent of lobar involvement (0:0%; 1, < 5%; 2:5-25%; 3:26-50%; 4:51-75%; 5, > 75%; range 0-5; global score 0-25). Data were matched with clinical stages and laboratory findings. Survival curves and univariate and multivariate analyses were performed to evaluate the role of CT score as a predictor of patients' outcome.

Results: Ground glass opacities were predominant in early-phase (≤ 7 days since symptoms' onset), while crazy-paving pattern, consolidation, and fibrosis characterized late-phase disease (> 7 days). CT score was significantly higher in critical and severe than in mild stage (p < 0.0001), and among late-phase than early-phase patients (p < 0.0001). CT score was significantly correlated with CRP (p < 0.0001, r = 0.6204) and D-dimer (p < 0.0001, r = 0.6625) levels. A CT score of ≥ 18 was associated with an increased mortality risk and was found to be predictive of death both in univariate (HR, 8.33; 95% CI, 3.19-21.73; p < 0.0001) and multivariate analysis (HR, 3.74; 95% CI, 1.10-12.77; p = 0.0348).

Conclusions: Our preliminary data suggest the potential role of CT score for predicting the outcome of SARS-CoV-2 patients. CT score is highly correlated with laboratory findings and disease severity and might be beneficial to speed-up diagnostic workflow in symptomatic cases.

Key points: • CT score is positively correlated with age, inflammatory biomarkers, severity of clinical categories, and disease phases. • A CT score ≥ 18 has shown to be highly predictive of patient's mortality in short-term follow-up. • Our multivariate analysis demonstrated that CT parenchymal assessment may more accurately reflect short-term outcome, providing a direct visualization of anatomic injury compared with non-specific inflammatory biomarkers.

Keywords: COVID-19; Pneumonia; Severe acute respiratory syndrome coronavirus 2; Tomography, X-ray computed.

Fig. 1

Different CT score of RLL involvement in COVID-19 pneumonia on axial, sagittal, and coronal images. 0% of RLL lobe involvement (a); < 5% of RLL involvement (b); 20% of RLL involvement (c); 40% of RLL lobe involvement (d); 70% of RLL involvement (e); > 75% of RLL involvement (f)

Fig. 2

Chest CT findings of COVID-19 pneumonia on axial images. GGO (a); crazy-paving pattern (GGO with superimposed inter- and intralobular septal thickening) (b); consolidation (c)

Fig. 3

Lobar CT scores (a) and CT score comparisons between lobes in right and left lungs (b) in SARS-CoV-2+ patients. Data are expressed as mean value ± SD (% of occurrences of involvement for each lobe) (a). Black dots express mean value, branches express SD (****p < 0.0001) (b). RUL, right upper lobe; ML, middle lobe; RLL, right lower lobe; LUL, left upper lobe; LLL, left lower lobe

Fig. 4

Comparisons between CT scores versus clinical categories (a) and disease phases (b) in SARS-CoV-2+ patients. Larger horizontal lines express mean values, shorter lines express SD (**** p < 0.0001)

Fig. 5

Kaplan-Meier survival curve. Estimated survival rate comparison between SARS-CoV-2+ patients with CT score < 18 and ≥ 18. Percentage of survival is expressed on the y-axis, while time (days) of the observation period is expressed on the x-axis