DISCUSSION
Thoracic CT is prevalently used to determine the diagnosis, follow-up and prognosis of COVID-19 pneumonia. As the stage of pneumonia in COVID-19 increases, disease-related mortality increases10,13. Different studies have reported varying rates of pulmonary involvement14. In this study, while the thoracic CT findings of 18 patients in Group 1 were normal, 8 patients had Stage 2 pneumonia, and 6 had Stage 3 pneumonia. None of the patients in this study who were diagnosed with COVID-19 had a comorbid condition, and no mortality occurred.
In addition to parameters that explain the characteristics and severity of lung parenchyma involvement, vascular measurements can also be analyzed on thoracic CT images. Enlarged PA diameters on CT images were studied as a method of screening and diagnosing PH15. PH can develop in relation to many causes such as idiopathic, genetic, cardiac, pulmonary, vascular and medication-related causes16. CT is suitable for evaluating interstitial lung disease, vascular anomalies and thromboembolic factors, which are among the secondary causes of PH17. In this study, it was found that the PA diameters of the pediatric children who had COVID-19 infection on their thoracic CT images were larger. A single CT examination in pediatric COVID-19 patients might not provide clear information about the etiology of PA expansion. However, the demographic characteristics of the patients and the absence of comorbid diseases suggested that the cause of the PA expansion was an acute complication developing secondarily to the COVID-19 infection. Still, COVID-19 pneumonia can present in the form of hypoxemia as a result of ventilation-perfusion mismatch, increased PVR and expansion in the diameter of PA.
The morphology of IVC is frequently used to estimate right atrial pressure; however,the relationship between IVC morphology and RV outcomes has not been clarified completely18. Dilated IVC cases were found to be associated with RV dysfunction, high central venous pressure, and high pulmonary artery pressure19. High PVR can lead to IVC dilatation along with PH and RV deficiency. Some studies showed that IVC dilatation was one of the early indicators of disrupted hemodynamics in shock patients19. The mechanism of RV dilatation is multifactorial, and it involves thrombotic events, hypoxemic vasoconstriction, cytokines and direct viral damage. In COVID-19 patients, RV dilatation was determined to be associated with a poor prognosis20. In this study, the diameter of IVC was significantly larger in the COVID-19 patients, but no significant finding was detected about RV dilatation.
In pediatric patients, the laboratory findings of COVID-19 are non-specific. Leukocyte and platelet counts may be normal, increased, or decreased4,21. Severe infection is frequently accompanied by lymphopenia22. In this study, in Group 1, 12 patients (40%) had leukopenia, and 3 (9.3%) had lymphopenia. While the leukocyte counts in Group 2 were significantly higher, there was no significant difference between Groups 1 and 2 in terms of the other whole blood parameters. Likewise, in most COVID-19 patients, CRP, ferritin, fibrinogen, D-dimer, LDH, CPK, ALT and AST levels may be found higher in proportion to the severity of the infection4. There was no significant difference between the two groups in this study regarding their CRP, ferritin, D-dimer, fibrinogen, LDH, CPK or AST values among biochemical parameters. The finding that clinical symptoms of COVID-19 emerged in Group 1 without a noticeable increase in acute phase reactants may be an indicator that different immune and inflammatory mechanisms are in place in children. Although these findings could partly explain the milder course of COVID-19 in children than in adults, they suggested that the mechanism is more complex. Liver damage can be seen in COVID-19 infections. The mechanisms of this damage may include direct cholangiocyte and hepatocyte damage or accompanying conditions such as hypoxia, sepsis and multiorgan dysfunction caused by antiviral medication use, systemic inflammatory response and respiratory distress syndrome23. Temporary disruptions in liver function tests may be encountered in COVID-19 infection cases, and these might not affect liver-related morbidity and mortality23. In this study, the ALT levels of Group 1 were significantly higher than those of Group 2. Anomalies in liver function tests are usually encountered alongside increased enzyme activities in muscles and the heart. In COVID-19 cases, myocardial injury defined by increased troponin levels occurs especially due to hypoxia, sepsis, systemic inflammation, pulmonary thrombosis and embolism, in addition to severe respiratory airway infection and non-ischemic myocardial processes like cardiac adrenergic hyperstimulation during a cytokine storm24. In this study, the troponin I levels were higher in Group 1 than Group 2, but the difference was not statistically significant.There was no significant difference between the groups regarding their D-dimer levels. Many studies have demonstrated that increased D-dimer levels in adult COVID-19 patients are an indicator of PTE25,26. COVID-19-related PTE cases in the pediatric population are very rare27. This suggests that there was no increased risk of PTE in the patients in Group 1, and their high troponin I levels could be associated with hypoxia and systemic inflammatory response.
Consequently, the results of this study indicated that increased diameters of PA and IVC as a result of increased inflammation, high vascular resistance and hypoxemia in pediatric COVID-19 patients may be an early warning sign related to potential cardiopulmonary complications. To propose an exact explanation on this topic, there is a need for more comprehensive studies supported by larger datasets.