COVID-19 pneumonia: microvascular disease revealed on pulmonary dual-energy computed tomography angiography

Increased prevalence of acute pulmonary embolism in COVID-19 has been reported in few recent studies. Some works have highlighted pathological changes on lung microvasculature with local pulmonary intravascular coagulopathy that may explain pulmonary artery thrombosis found on pulmonary computed tomography (CT) angiography. The objective of our study was to describe lung perfusion disorders assessed by pulmonary dual-energy CT (DECT) angiography in severe COVID-19 patients.

This single center retrospective study included 85 consecutive patients with a reverse transcriptase-polymerase chain reaction diagnosis of SARS-CoV-2 who underwent a pulmonary DECT angiography between March 16^th 2020 and April 22^th 2020. Pulmonary DECT angiography was performed when the patient had severe clinical symptoms or suffered from active neoplasia or immunosuppression. Two chest radiologists performed pulmonary angiography analysis in search of pulmonary artery thrombosis and a blinded semi quantitative analysis of iodine color maps focusing on the presence of parenchymal ischemia. The lung parenchyma was divided into volumes based on HU values. DECT analysis included lung segmentation, total lungs volume and distribution of lung perfusion assessment.

Twenty-nine patients (34%) were diagnosed with pulmonary artery thrombosis, mainly segmental (83%). Semi-quantitative analysis revealed parenchymal ischemia in 68% patients of the overall population, with no significant difference regarding absence or presence of pulmonary artery thrombosis (23 vs. 35, P=0.144). Inter-reader agreement of parenchymal ischemia between reader 1 and 2 was substantial [0.74; interquartile range (IQR): 0.59-0.89]. Volume of ischemia was significantly higher in patients with pulmonary artery thrombosis [29 (IQR, 8-100) vs. 8 (IQR, 0-45) cm³, P=0.041]. Lung parenchyma was divided between normal parenchyma (59%, of which 34% was hypoperfused), ground glass opacities (10%, of which 20% was hypoperfused) and consolidation (31%, of which 10% was hypoperfused).

Pulmonary perfusion evaluated by iodine concentration maps shows extreme heterogeneity in COVID-19 patients and lower iodine levels in normal parenchyma. Pulmonary ischemic areas were more frequent and larger in patients with pulmonary artery thrombosis. Pulmonary DECT angiography revealed a significant number of pulmonary ischemic areas even in the absence of visible pulmonary arterial thrombosis. This may reflect microthrombosis associated with COVID-19 pneumonia.