The presence of aerated lung in apposition to the pleura can be inferred by the presence of "lung sliding'' and A-lines ¹⁰. The former is a product of the translation of the visceral and parietal pleura against one another ⁴, and the latter a consequence of the large acoustic impedance difference between an air-filled structure and the overlying soft tissue.

Pulmonary consolidations that abut the pleura allow transmission of ultrasound waves, although with the loss of normal A-line artifacts. Further sonographic differentiation relies upon evaluation of the homogeneity and echogenicity of the lesion, as well as the shape, margin characteristics, and presence or absence of air bronchograms ^1,2.

In this case, pneumonia is the most likely pathological entity given both the clinical context and imaging findings.  Bacterial pneumonias typically display 'hepatization' early in their course ^1,2, with an echogenicity approximating that of the liver ⁵, save for the characteristic fine, branching echogenic structures which move with respiration. Some authors contend the presence of these dynamic air bronchograms ¹ are not only highly specific for pneumonic consolidation, but for a bacterial etiology ^1,2.

The static echoic foci scattered throughout the consolidation represent trapped pockets of air, vaguely reminiscent of the roentgenographic ''air alveologram'' as described by Dr. Benjamin Felson. These subcentimeter pockets are also found in other processes such as obstructive atelectasis.

Key learning points:

• at the interface between pleura and aerated lung total reflection of sound energy occurs
• loss of aeration allows imaging beyond this interface ^3,11
• some features of pneumonic consolidation
  • loss of "A-Lines''
  • "liver-like" echogenicity
  • dynamic air bronchograms
  • ill-defined margins