Pneumomediastinum

Differential diagnosis:

• Blunt trauma: most commonly due to alveolar rupture and subsequent dissection along the bronchoalveolar sheath followed by air spreading to the mediastinum (the Macklin effect)
• Penetrating trauma
• Esophageal and/or tracheal perforation
• Esophageal rupture (Boerhaave’s Syndrome): classically associated with forceful vomiting but can also occur with certain chemical ingestions or button-battery ingestions
• Non-traumatic alveolar rupture: generally occurs with high intra-thoracic pressure such as vigorous valsalva maneuver, excessive coughing, forceful crying, change in environmental pressure. Risk factors include asthma, COPD, interstitial lung disease, lung malignancy, respiratory illness, recreational drug use, child birth, scuba diving, airline passengers. 
• Bowel rupture: air in the abdominal cavity tracts up into the chest
• Iatrogenic following surgeries and procedures
• Spontaneous pneumomediastinum (no known cause): this is most classically seen in young, otherwise healthy males

 Work-up/Interventions:

• As with every patient determine sick vs. not sick. Most patients are asymptomatic and the pneumomediastinum will spontaneously resolve. These patients should be observed for 24 hours. If sick the patient will need further evaluation and possible treatment.
• Malignant pneumomediastinum is the development of tension pneumomediastinum with elevated mediastinal pressures resulting in cardiac pressure, decreased venous return, and decreased cardiac output.
• Blunt trauma:
• If the patient is symptomatic search for injuries to the larynx, trachea, major bronchi, pharynx, or esophagus using techniques such as bronchoscopy and esophagoscopy.
• Penetrating trauma:
• Typically requires further evaluation such as esophagography, esophagoscopy, and/or surgical exploration
• Non-traumatic esophageal rupture:
• Patients with esophageal rupture are usually ill-appearing, typically tachycardic, febrile, dyspneic, or diaphoretic.
• These patients require rapid recognition, aggressive fluid resuscitation, broad spectrum antibiotics, and definitive surgical repair.
• The mortality rate is approximately 35% in all patients.
• If surgical intervention is delayed >24 hours the mortality rate rises to approximately 50% and higher thereafter with 100% mortality without treatment.  

References:

1. Stapczynski, J. S., & Tintinalli, J. E. (2011). Tintinalli's emergency medicine: A comprehensive study guide (7th ed.). New York, N.Y.: McGraw-Hill Education LLC.. 
2. Kouritas VK, Papagiannopoulos K, Lazaridis G, et al. Pneumomediastinum. Journal of Thoracic Disease. 2015;7(Suppl 1):S44-S49. doi:10.3978/j.issn.2072-1439.2015.01.11.