COVID-19 pneumonia: Perfusion abnormalities shown on subtraction CT angiography in apparently well-ventilated lungs. A prospective cohort study

Abstract

Purpose: To evaluate whether a subtraction CT angiography (sCTA) perfusion score may have prognostic value in patients with COVID-19 pneumonia.

Method: This prospective cohort study included adult patients with RT-PCR-confirmed SARS-CoV-2 infection admitted to the ED and a sCTA performed within 24 h of admission between June and September 2020. Perfusion abnormalities (PA) in areas of apparently spared lung parenchyma on conventional CT images were assessed with sCTA perfusion score. Airspace disease extension was assessed with CT severity scores, which were then correlated with clinical outcomes (admission to ICU, requirement of IMV, and death). Inter-rater reliability (IRR) was assessed using Cohen's Kappa. Independent predictors of adverse outcomes were evaluated by multivariable logistic regression analyses using the Hosmer and Lemeshow's test.

Results: 191 patients were included: 112 males (58%), median age of 60.8 years (SD ± 16.0). The IRR was very high (median Kappa statistic: 0.95). No association was found between perfusion CT scores and D-dimer levels (Kendall's Tau-B coefficient = 0.08, p = 0.16) or between PaO₂/FiO₂ ratios and D-dimer levels (Kendall's Tau-B coefficient = -0.10, p = 0.07). Multivariate analyses adjusting for parenchymal disease extension, vascular beaded appearance, pulmonary embolism, sex, and age showed that severe PA remained a significant predictor for ICU admission (AOR: 6.25, 95% CI 2.10-18.7, p = 0.001). The overall diagnostic capacity of this model was adequate (ROC AUC: 0.83; 95% CI 0.77-0.89).

Conclusions: The assessment of pulmonary perfusion abnormalities in areas of apparently spared lung parenchyma on conventional CT images via sCTA perfusion scoring has prognostic value in COVID-19 pneumonia.

Keywords: Angiotensin converting enzyme 2; COVID-19; Computed tomography angiography; Vasoconstriction; Ventilation-perfusion ratio.

Fig. 1

Study flow chart.

Fig. 2

PaO2/FiO2 ratios amongst hospitalized patients with COVID-19. Stratified by sCTA Perfusion Score.

Fig. 3

Pulmonary vascular abnormalities. A. Vascular dilatation. MIP CTA axial image shows lack of tapering of subsegmental pulmonary vessels (black arrows) running through an area of ground-glass opacity. Another contiguous vascular branch is evidenced with the expected normal tapering (white arrows). B. Vascular beading appearance. Axial CTA image shows significant and extensive fusiform or saccular-appearing dilatation of subsegmental pulmonary vessels (black arrows). This 62-year-old man had 5 days since symptom onset, was initially admitted to the ICU, managed with IMV and died 3 weeks after admission.

Fig. 4

Hard beam artifacts. Conventional and color map sCTA axial and coronal images. 62-year-old male patient. 6 days since symptom onset. PaO2/FiO2 ratio was 298. Moderate hypoperfusion area in apparently normal lung parenchyma (*). Right lung subpleural ground-glass opacities show increased perfusion within the opacities (small arrows). Streak artifacts due to beam hardening by highly concentrated contrast in the superior vena cava (large arrows). (For interpretation of the references to color in this figure legend, the reader is referred to the Web version of this article.)

Fig. 5

Perfusion abnormalities. A. Mild perfusion abnormalities. 65-year-old female patient, 10 days since symptom onset. PaO₂/FiO₂ ratio was 390. Slight increase in D-dimer (rise of 1.36-fold the normal maximum). Outpatient management and no requirement of supplemental oxygen support. Mild hypoperfusion area in apparently normal lung parenchyma (*). Ground-glass opacities in both inferior lobes show decreased perfusion within the opacity, with a peripheral halo of increased perfusion (white arrows). These findings could be explained by physiological hypoxic vasoconstriction. B. Moderate perfusion abnormalities. 21-year-old male patient, 4 days since symptom onset. PaO₂/FiO₂ ratio was 400. Moderate increase in D-dimer (rise of 1.91-fold the normal maximum). Outpatient management and admission to the hospital 2 days later with PaO2/FiO2 ratio 190. Admitted to the ICU, managed with IMV. Initially, the patient presented mild involvement of the pulmonary parenchyma, moderate perfusion abnormalities in apparently normal lung parenchyma (*) and prominent areas of increased perfusion in relation to the zones of ground-glass opacities (white arrows). C. Severe perfusion abnormalities. 76-year-old female patient, 7 days since symptom onset. PaO₂/FiO₂ ratio was 117. Moderate increase in D-dimer (rise of 1.96-fold the normal maximum). Admitted to the ICU, managed with IMV. She died 3 weeks after admission. Extensive lung involvement with patchy ground-glass opacities in both lungs with right predominance, with vascular dilatation in small peripheral subsegmental pulmonary arterial branches, some of them with a varicose appearance (black arrows). Severe perfusion abnormalities in apparently normal lung parenchyma (*) and in some areas with ground glass opacities. Some areas of ground-glass opacities show marked hyperperfusion, most probably due to vasoplegia (white arrows). Note that in some ground glass opacities there are hypoperfusion areas that could be explained by microthrombosis or more likely by endothelial dysfunction. Linear atelectasis with increased perfusion in lingular segment (small black arrows).

Fig. 6

Multivariable logistic regression. Prediction of Intensive Care Unit Admission.