Lower respiratory tract infection (LRTI) in children is a spectrum of illness that may affect the peripheral airways (bronchiolitis) or the alveoli (pneumonia), but these can occur sequentially or simultaneously. There has been a considerable decrease in the incidence and mortality from LRTIs in the past 20 years; however, they remain the single largest cause of death in children worldwide. Pneumonia can cause substantial morbidity in children, with potential development of various acute and chronic complications. In 2017, approximately 15% of mortality among children below 5 years old was due to pneumonia. The disease burden remains substantial in low-income and middle-income countries, where more than 90% of pneumonia deaths occur.
Etiologies of LRTI include various organisms, such as viruses, bacteria, bacteria-like organisms, mycobacteria, fungi, and parasites. Mixed pathogens, however, also can occur. Among hospitalized children with pneumonia, approximately 26% to 35% had mixed pathogens of various combinations believed to function synergistically and likely enhancing the severity of the infection.
Medical imaging has been used to confirm or exclude the presence of pneumonia, but it also is helpful in the evaluation of recurrent or persistent abnormalities, in assessment of acute or chronic complications, and to exclude other underlying pathologic processes. This article aims to review the various imaging modalities utilized in the evaluation of LRTIs in children, present systematic and evidence-based diagnostic imaging recommendations and algorithms, and discuss the spectrum of acute and chronic imaging manifestations of these conditions.
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