title: Pneumomediastinum revisited.
abstract: 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 distal esophageal rupture, air may migrate from the mediastinum into the pulmonary ligament. Pneumomediastinum may be difficult to differentiate from medial pneumothorax and pneumopericardium. Occasionally, normal anatomic structures (eg, major fissure, anterior junction line) may simulate air within the mediastinum. Iatrogenic entities that may simulate pneumomediastinum include helium in the balloon of an intraaortic assist device. 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.
authors.affiliation: Department of Radiology, University of Arizona, Tucson 85719, USA. cmzjz@hotmail.com
authors.forename: C M
authors.initials: CM
authors.lastname: Zylak
authors.forename: J R
authors.initials: JR
authors.lastname: Standen
authors.forename: G R
authors.initials: GR
authors.lastname: Barnes
authors.forename: C J
authors.initials: CJ
authors.lastname: Zylak
mesh_terms: D000293:Adolescent; D000328:Adult; D000368:Aged; D016477:Artifacts; D001995:Bronchography; D002675:Child, Preschool; D003937:Diagnosis, Differential; D003964:Diaphragm / Q000000981:diagnostic imaging; D004935:Esophageal Diseases / Q000000981:diagnostic imaging; D005260:Female; D006801:Humans; D007423:Intra-Aortic Balloon Pumping / Q000295:instrumentation; D008297:Male; D008478:Mediastinal Emphysema / Q000000981:diagnostic imaging* / Q000209:etiology; D008482:Mediastinum / Q000000981:diagnostic imaging; D010994:Pleura / Q000000981:diagnostic imaging; D011026:Pneumopericardium / Q000175:diagnosis; D011030:Pneumothorax / Q000175:diagnosis; D011856:Radiographic Image Enhancement; D012422:Rupture, Spontaneous; D013950:Thymus Gland / Q000000981:diagnostic imaging; D014057:Tomography, X-Ray Computed / Q000379:methods