2.3 The volume of the pneumothorax
Although lung ultrasound is sensitive for the diagnosis of pneumothorax,
it is unable to measure the volume of the pneumothorax. Jing Liu et
al.12 conducted a study to explore the accuracy and
reliability of ultrasonography for the diagnosis of neonatal
pneumothorax and found that the main ultrasonographic signs of
pneumothorax included
disappearance of lung sliding,
presence of a pleural line and A-line, presence of lung points in
children with mild to moderate pneumothorax, absence of lung points in
children with severe pneumothorax, absence of a B-line and lung
consolidation in the area of pneumothorax. The sensitivity, specificity,
positive predictive value and negative predictive value of lung sliding
disappearance and the presence of pleural lines and A-lines in
diagnosing pneumothorax were 100%. Raimondi et al.5reported that lung ultrasound had high accuracy in detecting
pneumothorax, was superior to clinical evaluation and shortened the time
of diagnosis and treatment. International evidence-based guidelines also
indicated that lung ultrasound was helpful to accurately detect
pneumothorax in neonates and children (Grade B)8. It
is worth noting that the absence of lung sliding was also observed in
other disorders, such as apnoea, acute respiratory distress syndrome,
pulmonary atelectasis, deep pneumonia, decreased lung compliance, and
foreign body aspiration. As a result, the diagnosis of
pneumothorax cannot rely on the
disappearance of lung sliding alone, but the presence of lung sliding
can exclude pneumothorax. In
addition, the usefulness of lung ultrasound in the determination of
pneumothorax size was not certain. Jing Liu et al.9found that lung points existed in children with mild to moderate
pneumothorax and disappeared in children with severe pneumothorax.
Volpicelli et al.13 proposed that lung ultrasound
could quantify the pneumothorax volume by locating lung points on the
chest wall, and the lateral progression of lung points on the chest wall
corresponded to an increase in the extent of pneumothorax. However, the
thickness of pneumothorax cannot be measured due to the total reflection
caused by the gas, and the usefulness of lung ultrasound for quantifying
the pneumothorax size needs further validation in practice.
Pulmonary interstitial emphysema
Pulmonary interstitial emphysema
cannot be diagnosed by lung ultrasound. One case study
reported14 the role of lung ultrasound in the
follow-up of localized interstitial emphysema. The infant again
presented tachypnoea after continuous positive airway pressure for 72
hours. Lung ultrasound revealed a normal pattern of the right lung and
non-coalescent B-lines on the right side, while thoracic computed
tomography showed localized interstitial emphysema of the left upper
lobe. This ultrasonic finding (non-coalescent B-line) was observed in
other lung diseases and was not specific for emphysema. In patients with
emphysema, lung ultrasound often showed normal sonographic
manifestations with the presence of lung sliding and an A-line due to
decreased elastance of airway distal to terminal bronchioles,
overinflation of the lung, increases in lung volume, and a widened
intercostal space. Therefore, lung ultrasound cannot diagnose emphysema.