Diagnosis and monitoring of COVID‐19 pneumonia in pregnant women: is lung ultrasound appropriate?

In their recently published article1, Buonsenso et al. recommend the use of lung ultrasound (LUS) for monitoring pregnant women with confirmed severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) infection. In all four cases they describe, the ultrasound features indicative of coronavirus disease 2019 (COVID-19) pneumonia were pleural line irregularities with vertical artifacts (B-lines), and in two of the cases, patchy areas of white lung. However, in our experience from our COVID-19 center, these findings are ‘imaging errors’ that have no diagnostic validity as they are non-specific, not quantifiable and subject to interoperator variability. B-lines are artifacts generated when the ultrasound beam crosses areas with different acoustic impedance, in this case the chest wall and lung air interface, which reduces its propagation speed2. An irregular pleural line with increased number of B-lines may be visible in several conditions, such as acute respiratory distress syndrome, heart failure, nephrotic syndrome, pre-eclampsia, bacterial pneumonia, minimal pleural effusion, hydropneumothorax, fibrosis, pulmonary contusion, exacerbations of chronic obstructive pulmonary disease and neoplastic lymphangitis2,3 (Figure 1). In contrast, B-lines are absent on intraoperative LUS scans in patients with interstitial lung disease, being imaging errors arising from the difference in acoustic impedance between the superficial and deeper structures4. It should also be considered that this pattern, which the authors indicate to be suggestive of SARS-CoV-2 infection, could instead indicate a different viral pneumonia, such as influenza A5. The number of B-lines and presence of pleural line abnormalities are dependent on the type of probe used, the angle of the probe on the thoracic cage and the physician’s experience. The set-up of the device, such as gain, presence or absence of harmonics, and electronic focusing of the image can also modify the appearance of these artifacts2, which is not mentioned in the article of Buonsenso et al.1. Due to lung air content and rib-cage hindrance, only about 70% of the pleural surface can be visualized by LUS, and therefore, pathological conditions can be examined only if they are adherent to this viewable area2. Typical features of COVID-19 on chest computed tomography (CT) include ground-glass opacity and consolidation, which are mainly distributed in the peripheral and posterior part of the lung6. However, these alterations are not always located in areas adherent to the pleural surface and/or accessible to LUS, therefore, there is a risk of Figure 1 (a) Computed tomographic image of chest (axial view), showing pulmonary carcinoma of right lung, partially adherent and infiltrating the pleura (arrow). (b) Ultrasound image obtained using 6-MHz convex probe and set up for thoracic study, showing increased thickness of irregular hyperechoic pleural line and coalescent B-lines below it (white lung appearance), with subpleural hypoechoic consolidation, as part of lung carcinoma (arrow).