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Thứ Sáu, 27 tháng 12, 2013

NEW SIGNS of PNEUMOTHORAX at LUNG ULTRASOUND






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 [9]. 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 [7]. 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 [10]. 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.


Septate pneumothorax: recurrent pneumothoraces after invasive therapeutic procedures are often characterized by abnormal ultrasound findings. In patients with failed pleurodesis, it is quite common to observe the typical ultrasound pattern of septate pneumothorax [11]. In this case, the absence of sliding may be combined with the persistence of B lines and lung pulse in the same scan (Additional file 2). While, in the majority of patients, visualization of B lines and lung pulse rules out pneumothorax, there are rare cases where the negative predictive power of B lines and lung pulse may be misleading. In the context of absent lung sliding, the small areas showing B lines and lung pulse correspond to small lung regions where the parietal and visceral pleura are still touching due to  the presence of septa (Figure 2). Demonstration of a lung point in other areas of the chest is a decisive step to conclude the examination and diagnose pneumothorax. A sonographic pattern that combines an absence of lung sliding but presence of B lines and/or lung pulse with presence of  a lung point is diagnostic of septate pneumothorax.


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 [12].


Figure 3: Opposition between the air/fluid patterns is the hydro-point.


Conclusion
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.

 
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