Occult pneumothorax, revisited

The entity of occult pneumothorax is more frequently recognized nowadays due to the the increasing diffusion of CT scan and thoracic ultrasonography in the evaluation of trauma patients. These diagnostic tools enabled us to detect small abnormalities not clinched by the traditional chest radiograph. The concept of occult pneumothorax has been thoroughly discussed amongst the literature [1-5]. In trauma patients, AP chest radiograph has been traditionally the initial diagnostic imaging study especially if a cervical-collar limits patient mobilization. With advent of the extended FAST examination (Focused Assessment with Sonography for Trauma), most centers now utilize eFAST before the initial screening chest Xray. This review describes the differences between AP chest radiograph and chest CT in early detection of a pneumothorax in a trauma patient.Occult pneumothorax is a pneumothorax that was not suspected clinically nor was evident on the plain radiograph but rather identified on computed tomography scan.Due to the increased utilization of CT chest and thoracic ultrasonography as the initial screening tests for thoracic and abdominal trauma, occult pneumothorax has been common. Most nonradiologists diagnose pneumothorax based on the visualization of a superior-lateral visceral pleural stripe on the upright chest radiograph. This is however not feasible in the supine chest radiograph unless there is a sizable pneumothorax. Unfortunately, because of clinical concerns in trauma patients regarding cervical spine immobilization, initial imaging in seriously injured patients typically consists of a supine AP chest X-ray that is insensitive for detecting pneumothorax. As illustrated in figure 1 after an initial AP chest radiograph failed to show evidence of pneumothorax, a CT chest performed immediately after the chest Xray revealed right-sided pneumothorax.The reported incidence of occult pneumothorax varies widely between 3.7% in injured children presenting to an emerge