Pneumomediastinum revisited

Pneumomediastinum may result from a variety of causes that may be either in trathoracic (eg, narrowed or plugged airway, straining against a closed glo ttis, blunt chest trauma) or extrathoracic (eg, sinus fracture, iatrogenic manipulation in dental extraction, perforation of a hollow viscus, alveolar rupture). The radiographic signs of pneumomediastinum depend on the depict ion of normal anatomic structures that are outlined by the air as it leaves the mediastinum. These signs include the thymic sail sign, "ring around th e artery" sign, tubular artery sign, double bronchial wall sign, continuous diaphragm sign, and extrapleural sign. In distal esophageal rupture, air m ay migrate from the mediastinum. into the pulmonary ligament. Pneumomediast inum may be difficult to differentiate from medial pneumothorax and pneumop ericardium. Occasionally, normal anatomic structures (eg, major fissure, an terior junction line) may simulate air within the mediastinum. Iatrogenic e ntities that may simulate pneumomediastinum include helium in the balloon o f an intraaortic assist device. In addition, pneumomediastinum may be simul ated by the Mach band effect, which manifests as a region of lucency adjace nt to structures with convex borders. The absence of an opaque line, which is typically seen in pneumomediastinum, can aid in differentiation. Compute d tomographic (CT) digital radiography and conventional CT can also be help ful in establishing or confirming the diagnosis.