Transthoracic ultrasonography to differentiate bullous emphysema from pneumothorax: a bright future in black and white.
Respected Editor, The case report by Lai et al.  was both interesting and informative. We agree with the usefulness of CT thorax to differentiate pneumothorax from giant bulla with double wall sign. Though CT offers the most accurate diagnostic information, it is difficult to transport unstable patient to a CT suite which is in a remote area from a resuscitative area or to wait for a specialized technician to perform it and a radiologist to interpret it. Traditionally, the presence of bullae and their advancement are recognized by chest radiography. At times, even forced expiratory films are used to demonstrate the existence of bullae . However, limitation is difficult to differentiate the hairline shadows produced by avascular bullae from irregular walls of a cavity or cysts in the lung parenchyma in an emergency setting and may easily be mistaken for a pneumothorax  sometimes. In this scenario, the bedside transthoracic ultrasonography has emerged as a reliable technique to detect and exclude pneumothorax which is now well accepted by the medical community. The effectiveness of ultrasound in detection of bullae and differentiate it from pneumothorax  is well documented. The lung sliding may be minimal because there may be little movement of the visceral pleura that covers the bulla. As there is no free air in the pleural space, the reverberation artifact that produces the 'comet tail artifacts' may be noticed in bullous disease. However, it is absent when the lung is collapsed as in pneumothorax and thereby helps to arrive at the diagnosis . Speedy and precise diagnosis of bullous emphysema from pneumothorax will assist in treatment, as the management of these two entities varies significantly. Many times patients presenting to the emergency departments were in extremis and call for an immediate decision making and delaying can be life threatening. In an emerging culture of protocol and guidelines regarding effectiveness of treatment, transthoracic ultrasonography may be considered in the emergency department to assure the high quality of health care given to patients.
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