Sonographic signs of complex pneumothorax
Double lung point: when for some reason the air of a pneumothorax is not free to float inside the pleural space, a minimal amount of pleural air may remain in the lateral or dorsal chest without migrating in the most superior area in a supine patient, which corresponds to the anterior-inferior chest zone. In this case, the operator may visualize two lung points, i.e. the alternating patterns of sliding and non-sliding lung intermittently appearing at the two opposite sides of the scan (Additional file 1) [7,8]. These two lung points represent the visualization of the two edges of the air trapped in the pleural space (Figure 1).
Pneumothorax with air trapping may be caused not only by pleural adherences in chronic pleural and pulmonary diseases but also by acute lung contusions in blunt torso trauma . Even without abnormal pleural adherences, very small spontaneous pneumothoraces may not have enough pressure to allow complete detachment of the pleural layers and the floating of air towards the most superior chest areas . Being aware of this condition or in case of strong suspicion, the operator should always complete the scan of the lateral chest in the supine patient to confirm lung siding even when this latter is first visualized in the parasternal anterior-inferior chest. In the unstable patient, this extension of the technique is less important. Presence of lung sliding in the anterior-inferior chest may conclude the ultrasound examination, unless the patient is intubated for pressure ventilation or is going to be transported by helicopter . In these two latter cases, the lateral chest should always be scanned to rule out even the smallest pneumothorax that may need to be monitored or warrant prophylactic drainage.
Figure 1: Visualization of the two edges of the air trapped in the pleural space.
Figure 2: The small areas showing B lines and lung pulse correspond to small pleural adherences.
Hydropneumothorax: iatrogenic pneumothorax following procedures of thoracentesis in pleural effusion is a well known complication. While interposition between the normally aerated lung and pneumothorax (air/air interface) is demonstrated in a lung ultrasound by the lung point sign, air/fluid interface in the pleural space gives a different sonographic pattern.
In hydropneumothorax, the pleural effusion is demonstrated by the visualization of space, usually anechoic, between the two pleural layers while pneumothorax gives the well-known A pattern, i.e. the reverberation of the chest wall image below the pleural line with A lines, absence of sliding or pulse and absence of B lines (Additional file 3). Opposition between these two patterns is the hydro-point (Figure 3). This recently described sonographic sign shares the same diagnostic power with the lung point for the diagnosis of pneumothorax .
Figure 3: Opposition between the air/fluid patterns is the hydro-point.
Lung ultrasound is rapidly spreading as a safe bedside methodology for the diagnosis of pneumothorax in different settings. Because of its increasing use in the clinical practice, observations of some unusual and complicated cases are also emerging. The conventional step-by-step sonographic technique and the four conventional ultrasound signs of pneumothorax should be slightly modified to consider the possibility of facing complex cases. Complicated pneumothorax may be encountered in many different settings, such as trauma patients, spontaneous pneumothorax, recurrent pneumothorax after pleurodesis and post-procedural pneumothorax. The operator should be aware and know how to interpret unusual sonographic signs and patterns, such as the double lung point, the septate pneumothorax and the hydro-point.