UOTW #67 Answer

Answer: Pneumomediastinum

This subxiphoid view shows no clear view of the heart, but there are a-lines and b-lines arising from the mediastinum.  Lung sliding is noted anteriorly, ruling out pneumothorax at this rib space.

  • Pneumomediastinum is defined as free air in the mediastinal cavity.1 It can occur spontaneously or in the setting of trauma,1 and is thought to be caused by an increase in intrathoracic pressure and air leaking from the airways or esophagus into the mediastinum.2 The gold standard for diagnosis is CT scan.
  • A-lines are a common reverberation artifact that can be seen generated from air filled structures, most commonly from the lungs.3
  • A-lines have been described to occur in the setting of pneumomediastinum in the emergency ultrasound literature1
  • Although research is limited, the best echocardiographic window for the evaluation of pneumomediastinum appears to be the subxiphoid window,1 although looking for free air in the neck in the setting of a suspected pneumomediastinum has also been described.4
  • Another important consideration on the differential is pneumopericardium. This has also been described, but its appearance has been reported to differ from pneumomediastinum. Pneumopericardium has been associated with b-lines generated in the pericardial sac, rather than a-lines.5

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  1. Zachariah S, Gharahbaghian L, Perera P, Joshi N. Spontaneous pneumomediastinum on bedside ultrasound: case report and review of the literature. The western journal of emergency medicine. 16(2):321-4. 2015. [pubmed]

  2. Testa A, Candelli M, Pignataro G, Costantini AM, Pirronti T, Silveri NG. Sonographic detection of spontaneous pneumomediastinum. Journal of ultrasound in medicine : official journal of the American Institute of Ultrasound in Medicine. 27(10):1507-9. 2008. [pubmed]

  3. Lobo V, Weingrow D, Perea P, Williams SR, Gharahbaghian L. Thoracic Ultrasonography. Critical care clinics. 30(1):93-117 2014

  4. Testa A, Candelli M, Pignataro G, Costantini AM, Pirronti T, Silveri NG. Sonographic detection of spontaneous pneumomediastinum. Journal of ultrasound in medicine : official journal of the American Institute of Ultrasound in Medicine. 27(10):1507-9. 2008. [pubmed]

  5. Bobbia X, Claret PG, Muller L, de La Coussaye JE. Pneumopericardium diagnosis by point-of-care ultrasonography. Journal of clinical ultrasound : JCU. 41(4):235-7. 2013. [pubmed]