2.5 Pathogen of pneumonia
The diagnosis of pneumonia by lung ultrasound should be combined with
the medical history. A distinction between infected and noninfected
consolidation cannot be made on lung ultrasound. The ultrasound images
of pneumonia include the presence of pulmonary consolidation with
irregular margins and dynamic air bronchograms, pleural effusion,
pleural line abnormalities or the absence of lung sliding, and
alveolar–interstitial patterns in the adjacent areas. Since lobar
pneumonia occurs in lung segments and lobes, and the sensitivity of
ultrasonography for diagnosing lobar pneumonia is high, the sonographic
appearances of lobar pneumonia include large consolidation with dynamic
air bronchograms and/or pleural effusions. It was reported that large
lung consolidation with irregular margins had a sensitivity of 100% and
specificity of 100% for the diagnosis of neonatal
pneumonia15. Of note, the detection of consolidation
by lung ultrasound is associated with the size of the consolidation and
the distance between the consolidation and the pleural surface. The
smaller consolidations far away from the pleura and areas under the bony
structure may be missed by lung ultrasound. Large lung consolidations
can be observed in NRDS, acute respiratory distress syndrome and MAS;
small consolidations can be observed in NRDS characterized by
progressive dyspnoea shortly after birth and bronchopulmonary dysplasia
with long-term dependence on oxygen, and thus, a medical history is
crucial for the differential
diagnosis. Additionally, although a distinction between a small
consolidation greater than 1 cm and one less than 1 cm had been studied,
the diagnostic threshold of the consolidation size for pneumonia was not
presented explicitly in the study16,17. It was
reported in the literature18 that viral pneumonia
presented with subpleural small consolidation (diameter<1 cm)
and/or a B-line and that bacterial pneumonia presented with lung
consolidation with dynamic air bronchograms. We argued that the cut-off
value of a consolidation diameter < 1 cm for distinguishing
between bacterial and viral infections was controversial, although a
small consolidation with a diameter < 1 cm was undetectable by
chest radiography. Several studies19,20 reported that
acute bronchiolitis presented with irregular pleural lines, subpleural
consolidation and interstitial syndrome, which was similar to viral
pneumonia. A study17 evaluated the diagnostic accuracy
of lung ultrasound for the detection of pneumonia in hospitalized
children with acute bronchiolitis, reporting that 10 cases showed
false-positive ultrasonic findings and that 9 of the cases consisted of
subcentimetric pneumonia. Therefore, for neonates with small subpleural
consolidations, lung ultrasound is not useful to distinguish between
bacteria or viral pneumonia or acute bronchiolitis. The differential
diagnosis requires a combination of clinical examination and medical
history.