Coronavirus disease 2019 is caused by severe acute respiratory syndrome coronavirus 2 also known as SARS-CoV-2. The virus is a member of the coronavirus family which is a group of single-stranded RNA viruses that have surface-like projections that have the appearance similar to a crown.
The virus is felt to be transmitted from a zoonotic source in the natural reservoir is favored to be bats, similar to that observed in Prior epidemics caused by SARS and MERS. The virus was first reported in humans as a series of unexplained cases of pneumonia in Wuhan, China in December of 2019. Since that time, the virus rapidly spread worldwide now involving more than 200 countries and territories and has been called a pandemic by the World Health Organization. Most recently, the World Health Organization reported nearly 3.6 million cases of coronavirus disease 2019 worldwide and nearly 250,000 deaths.
COVID-19 is predominantly transmitted through inhalation of virus particles, however there are reports of spread through direct contact with conjunctival membranes. The virus causes disease by binding of the spike proteins to ACE2 receptors and is predominately expressed by alveolar epithelial cells. This leads to elevated levels of ACE2 and subsequent alveolar damage. There have also been reports of elevated pro-inflammatory cytokines and chemokines in COVID-19 patients, suggesting a role of immune dysregulation in disease pathogenesis.
When thinking about COVID-19 in pediatric patients there are a few factors which are important to keep in mind. First, pediatric patients have immature lung anatomy and developing immune systems, which can lead to differences in the clinical and radiographic presentation of disease. One example of this is the hypothesis that children have an overall less severe clinical course due to lower maturity and function of ACE2. However, there have been increasing reports of severe and fatal cases of pediatric COVID-19, some of which relate to viral-induced cardiomyopathy and shock.
Other factors to keep in mind with children are that they play an important role in disease transmission and that they can always tell us how they’re feeling. Children who are too young to talk or have developmental delays may have an inability to communicate symptoms, which can lead to diagnostic difficulty. Additionally pediatric patients have increased radiation sensitivity compared to adults, and this should be kept in mind when making decisions about ordering radiographic studies.
The clinical presentation of pediatric COVID-19 is often nonspecific with fever and cough reported as the most common symptoms. Additional symptoms such as dyspnea, abdominal pain, chest pain, and rhinorrhea are reported with less frequency. Laboratory values are often nonspecific as well and the CVC tends to be normal, however there have been reports of neutropenia, thrombocytopenia, and lymphopenia in pediatric patients. Inflammatory markers may be elevated including CRP or ESR, however this is variably seen. In severe cases, there have been reports of altered coagulation, elevated LFT’s, elevated LDH, and elevated D-dimer. On chest radiograph, the most suggestive imaging pattern for pediatric COVID-19 related infection is bilateral, peripheral predominant ground glass and/or consolidated opacities in the mid and lower lung zones.
However chest radiograph may be normal, or may present with an indeterminate pattern. CT tends to be more sensitive in chest radiograph and often shows a greater extent of disease in patients who had subtle chest radiograph abnormalities or shows abnormality in patients who initially had negative chest radiographs. On chest CT, the most typical pattern for pediatric COVID-19 related disease is bilateral ground glass opacities and/or consolidation in a peripheral or subpleural location predominantly in the mid and lower lung zones.
There are few features which have been reported in pediatric patients that are different than adult patients and bear attention. First, the halo sign has been reported early in the disease process for pediatric patients, which is a focal area of consolidation with a surrounding rim of ground glass. Second, pediatric patients have been shown to have bronchial wall thickening and peribronchovascular opacities more frequently than adults, although this is not the typical pattern. Finally, pediatric patients are less likely to have a pattern of crazy paving related to interlobular septal thickening compared to adults. The findings of lymphadenopathy in pleural effusion are extremely rare on CT and if you see these findings, you should think of alternative diagnoses.
The progression of imaging findings on chest CT in pediatric COVID-19 gives insight into the underlying infectious process in the lungs. During the early phase of disease, the infection presents with focal consolidative opacity and a rim of ground glass indicating localized inflammation with adjacent vascular congestion. As inflammation begins to spread to adjacent alveoli, a pattern of alveolitis develops, which on CT has the appearance of more diffuse ground glass. As the alveoli become more filled with fluid and inflammatory cells, the ground glass becomes more consolidative, indicating a developed phase of infection.