Radiographics : a review publication of the Radiological Society of North America, Inc
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Pneumomediastinum may result from a variety of causes that may be either intrathoracic (eg, narrowed or plugged airway, straining against a closed glottis, blunt chest trauma, alveolar rupture) or extrathoracic (eg, sinus fracture, iatrogenic manipulation in dental extraction, perforation of a hollow viscus [corrected]. The radiographic signs of pneumomediastinum depend on the depiction of normal anatomic structures that are outlined by the air as it leaves the mediastinum. These signs include the thymic sail sign, "ring around the artery" sign, tubular artery sign, double bronchial wall sign, continuous diaphragm sign, and extrapleural sign. ⋯ In addition, pneumomediastinum may be simulated by the Mach band effect, which manifests as a region of lucency adjacent to structures with convex borders. The absence of an opaque line, which is typically seen in pneumomediastinum, can aid in differentiation. Computed tomographic (CT) digital radiography and conventional CT can also be helpful in establishing or confirming the diagnosis.
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Magnetic resonance imaging is the method of choice for evaluating patients with a nontraumatic brachial plexopathy. Although there is a wide range of disease processes that may cause a brachial plexopathy, radiation fibrosis, primary and metastatic lung cancer, and metastatic breast cancer account for almost three-fourths of the causes. Radiation fibrosis, the most common cause in our series, may occur several months to years after the completion of therapy. ⋯ Lung cancer arising in the lung apex may invade the lower portion of the brachial plexus. Many tumors may metastasize to the brachial plexus, causing a brachial plexopathy. Breast cancer is the most likely to metastasize because major lymphatic drainage routes for the breast course through the apex of the axilla.