Unapparent Parenchymal Density Changes in the Negative CT Examinations of Patients with COVID-19 Pneumonia

Abstract

Purpose: In this study, we aimed to compare the densities of affected lobes versus normal-appearing contralateral lobes in the initial CT of COVID-19 patients who had visually negative initial CT examinations.

Methods: Twenty-one lung lobes of 18 patients with a proven diagnosis of COVID- 19 disease, who had more than one CT scan at an interval of three–six days, were included in the study. Lung segmentation and volumetric density calculations of the affected and normal-appearing contralateral lobes were performed using dedicated software. The selection of the affected lobes was determined according to the findings in the follow-up CT. The density data of the affected lung lobe and opposite normal-appearing lung were calculated in the initial CT, recorded for each patient, and compared statistically.

Results: The mean duration between the first and second CT examinations was 4.5±1.3 days (range, 3-6 days). The mean density of the lung lobe was -777.6±48.3 and -817.2±20.4 HU for the affected and normal-appearing sides, respectively (p=0.003). The differences in densities between the affected and normal-appearing lobes were moderately correlated with age (p=0.028, r=0.516) whereas the time interval between the examinations showed a moderately negative correlation with age (p=0.003, r=-0.647). Conclusions: The early CT scan of COVID-19 disease shows altered CT densities of the affected lung lobe compared to the normal-appearing side in the presence of visually negative CT results. These changes progress into visible imaging findings of the disease within three to six days.

Keywords: COVID-19; Computed tomography; Normal appearing lung; Density