4 | DISCUSSION
There has been limited data regarding the usefulness of LUS in children with COVID‑19. Given the paucity of children-related articles in scientific literature, Norbedo et al. reviewed only 2 studies on ultrasound use for COVID-19 suspected pediatric patients and compared them with the published findings in adult patients. They demonstrated that in the context of pediatric patient evaluation use of LUS could aid in detecting COVID-19 pneumonia, even if a small case series reported encouraging results8. Caroselli et al. identified only seven studies using LUS to diagnose SARS-CoV-2 infection in newborns and children and compared it with published findings, including 117 studies describing the use of chest X-ray or chest computed tomography in pediatric patients with COVID-19, and the review indicates that the use of LUS should be encouraged in pediatric patients, who are at highest risk of complications from medical ionizing radiation28. To the best of our knowledge, this is the first systematic review study of the pediatric age group to evaluate the use of LUS versus CXR and chest CT in children with COVID‐19. In the present study, we identified 33 patients (14.11%) with lung abnormalities on LUS who had a normal chest radiograph, but no patients with normal lung US had abnormalities on the CXR. Therefore, we conclude that lung ultrasound is more accurate than CXR in identifying patients with COVID-19 pneumonia. Moreover, we identified 3 patients(6%) with lung abnormalities on chest LUS who had a normal CT in this review. Feng et al. reported two cases (out of 5 children) and Hizal et al. reported only one case (out of 28 children) of discordance of LUS and chest CT results, respectively, an increased B‐line in the lower lobe and normal chest CT findings17,.21. All three patients underwent LUS and CT at the time of admission to the hospital with mild to moderate symptoms. Musolino et al. report that more B lines were presented in children in the early stage of the COVID-19 children20. Furthermore, the cause of this inconsistency could be that CT scan was suggested as a screening method due to rapid identification of pulmonary images typical of COVID-19 such as the ground-glass opacity; however, it is also demonstrated that the pathological findings are pathological are often found later29. Meanwhile, the fact that COVID‐19 lung involvement begins predominantly from peripheral regions of the lung creates an advantage in detecting these lesions via LUS. Consequently, the abnormal LUS findings detected in patients with normal CT made us believe that LUS is a sensitive diagnostic tool of child COVID‐19 pneumonia, especially in the early stage of the disease and mild cases.
To avoid excessive radiation exposure and contamination of suites, personnel and equipment, the British Paediatric Respiratory Society recommended that chest CT should be reserved for unstable cases with increasingly clinical deterioration or if surgery cannot be postponed30. However, as is widely known, the clinical COVID-19 manifestations in children are mild or moderate compared to the adult population; therefore, there is an urgent need to understand the correlation between lung US findings and clinical severity in this desease31. In our review, only 3 relevant studies were included. The study of Giorno et al. was the first in the pediatric COVID-19 population to analyze lung US aeration scores and demonstrated that patients that classified as moderate and severe/critical had major abnormalities on lung US and consequently higher lung US aeration scores15. They do not have statistical power to confirm the lung US aeration score as a disease severity predictor given the small sample size. Li et al. retrospectively evaluated neonates with confirmed COVID‐19 as well as 11 age‐ and gender‐matched controls (control group) simultaneously and the LUSS was significantly higher in the COVID‐19 group(P <0.05), suggesting that might be an additional tool to help clinicians in risk stratification18. However, this was a retrospective study, and few positive cases were not enrolled due to a lack of timely LUS examination. Musolino et al. conducted a prospective observational study, including 30 patients with swab‐confirmed COVID‐19 infection and the patients were subjected to an LUS within 6 h from admission and after 96 h. The results showed that LUS had a 90.9% sensitivity in detecting signs of lung involvement by COVID‐19. Importantly, the LUS allowed differentiating between those with mild or moderate disease20. Since the ultrasound aspects described in the study are not pathognomonic of SARS-CoV‐2 infection and also found in the course of other lung diseases, the result is still encouraging. In view of this, LUS can be useful to identify patients with lung involvement and in staging their severity in this new disease.
As residual lung fibrosis may develop after viral infections also in children with COVID‐19, a longitudinal follow‐up study with invasive or less invasive imaging techniques would be of remarkable value. Interestingly, only one study about the application of LUS in longitudinal follow-up on COVID-19 children was founded. This limited use of LUS in children, if reflective of daily clinical practice, contradicts available scientific evidence. Denina et al., using LUS done a follow-up for 28 patients to study the sequelae of COVID-19 in children and lung ultrasound findings correlated with the clinical improvement, showing a complete normalization within 5 weeks from hospital discharge in the majority of patients14. Therefore, we believe it is urgent to prompt further investigation into longitudinal follow‐up study with LUS and an extended time follow-up is also necessary.
Finally, research on COVID-19 pneumonia diagnosis is hampered by the difficulties in obtaining a systematic comparison with a CT scan. Despite, we believe that it provides valuable information, as there is limited data regarding pediatric patients with this condition. In addition, all the sonographers from the literatures were not blinded to clinical information because lung US assessment is performed regularly as an extension of the physical examination. Therefore, we recommended that LUS findings always should be interpreted in light of the clinical context.
Consequently, we suggest that LUS is a useful tool in diagnosing children with COVID‐19 during the pandemic. When LUS is used in the initial diagnostic steps in early diagnosis and follow-up monitoring of COVID-19 pneumonia in children, reduction in chest CT assessments may be possible.