CT findings in "Post-Covid": residua from acute pneumonia or "Post-Covid-ILD"?

Abstract

The aim of this study was to evaluate if CT findings in patients with pulmonary Post Covid syndrome represent residua after acute pneumonia or if SARS-CoV 2 induces a true ILD. Consecutive patients with status post acute Covid-19 pneumonia and persisting pulmonary symptoms were enrolled. Inclusion criteria were availability of at least one chest CT performed in the acute phase and at least one chest CT performed at least 80 days after symptom onset. In both acute and chronic phase CTs 14 CT features as well as distribution and extent of opacifications were independently determined by two chest radiologists. Evolution of every single CT lesion over time was registered intraindividually for every patient. Moreover, lung abnormalities were automatically segmented using a pre-trained nnU-Net model and volume as well as density of parenchymal lesions were plotted over the entire course of disease including all available CTs. 29 patients (median age 59 years, IQR 8, 22 men) were enrolled. Follow-up period was 80-242 days (mean 134). 152/157 (97 %) lesions in the chronic phase CTs represented residua of lung pathology in the acute phase. Subjective and objective evaluation of serial CTs showed that CT abnormalities were stable in location and continuously decreasing in extent and density. The results of our study support the hypothesis that CT abnormalities in the chronic phase after Covid-19 pneumonia represent residua in terms of prolonged healing of acute infection. We did not find any evidence for a Post Covid ILD.

Figure 1.

Course of CT findings. a) – c) Axial contrast-enhanced CT scans of a 63 yo male a) in the acute phase 23 days after symptom onset, b) in the chronic phase 97 days after symptom onset and c) in the chronic phase 154 days after symptom onset. In the acute phase consolidation and less so GGO are present predominantly in the periphery of the posterior lung. Large parts of the opacifications are sharply demarcated (arrows). During follow-up the opacifications are stable in location but continuously decreasing in extent and density. Residual GGO (arrows) and linear opacities (arrowheads) remain. Also bronchial wall thickening is seen. There are no de novo abnormalities. d)-f) Axial contrast-enhanced and non-enhanced CT scans of a 56 yo male d) in the acute phase 5 days after symptom onset, e) in the acute phase 55 days after symptom onset and f) 63 days after symptom onset as well as g) in the chronic phase 175 days after symptom onset. The CTs in the acute phase show a pattern characteristic for COVID-19 pneumonia turning into a pattern of ARDS. During follow-up GGO and consolidation resolve while bronchial dilatation (arrows) and reticulations (arrowheads) develop. There are no de novo abnormalities.

Figure 2a:

Segmentation of pulmonary opacities in CTs throughout the course of disease. HRCT on day 20, 41 and 137 after symptom onset. Automatic segmentation of lung lesions using a pre-trained nnU-Net model. Pathologic lesions are marked in red. Stable localization and continuous decrease of volume of altered lung parenchyma is seen.

Figure 2b.

Patient wise calculation of the percentage of opacified lung tissue. Each graph represents a patient, each point on the graph represents a scan. All graphs show a continuous decrease of volume of opacified lung tissue throughout the chronic phase.

Figure 2c.

Patient wise calculation of mean lung tissue density. Each graph represents a patient, each time point on the graph represents a scan. All graphs show a continuous decrease of mean density of lung tissue throughout the chronic phase.