Pneumomediastinum

Aka: Pneumomediastinum, Mediastinal Emphysema

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II. Definitions

  1. Pneumomediastinum
    1. Free air within the mediastinal space

III. Pathophysiology

  1. Sources
    1. Spontaneous rupture of alveolus or bleb
    2. Tracheobronchial Injury (Trauma)
    3. Boerhaave's Syndrome (Esophageal Rupture)
  2. Results from increased pressure gradient
    1. Negative (Inhalation)
    2. Positive (Valsalva)
  3. Air tracks along vessels and Bronchi
  4. Air coalesces in mediastinum

IV. Causes

  1. Secondary Pneumomediastinum (may be life-threatening)
    1. Tracheobronchial Injury (Trauma, Foreign Body Aspiration)
    2. Boerhaave's Syndrome (Esophageal Rupture, sharp Foreign Body Ingestion)
    3. Blunt Chest Injury (Pneumothorax, Rib Fracture, Sternal Fracture)
  2. Spontaneous Pneumomediastinum (tends to be benign)
    1. Inhalation Drug Use (e.g. Huffing)
      1. Inhalation Drug Users may perform action similar to Muller Maneuver
      2. Forced inspiration against a closed mouth and nose (opposite Valsalva Maneuver)
    2. Asthma
    3. Coughing
    4. Vomiting or Retching
    5. Weight lifting
    6. Vaginal Delivery
    7. Mechanical Ventilation

V. Symptoms

  1. Sore Throat
  2. Dyspnea
  3. Pleuritic Chest Pain
    1. Worse with lying
    2. Better with sitting

VI. Signs

  1. Subcutaneous Emphysema
  2. Hamman's Crunch (50%)
    1. Precordial systolic crepitation sound heard synchronous with heart beat
  3. Hamman Sign
    1. Diminished heart sounds

VII. Differential Diagnosis

  1. Esophageal Perforation
  2. Pneumothorax

VIII. Labs

  1. Complete Blood Count
  2. C-Reactive Protein
  3. Serum Lactate

IX. Imaging

  1. Chest XRay
    1. As many as 50% Pneumomediastinum cases are missed on PA Chest XRay
      1. Observe for a stripe of air extending superiorly from hilum, parallel to mediastinum
      2. Outlines mediastinal anatomy (pulmonary artery, major aortic branches and Bronchial wall)
    2. Review Lateral Chest XRay carefully
    3. Consider lateral neck XRay
      1. Air tracks between posterior pharyngeal wall and Vertebrae
      2. Air is more easily seen on this view, than Chest XRay
    4. Named Signs
      1. Naclerio V Sign
        1. Sharp, well demarcated "V" along the left heart border and left diaphragm
      2. Continuous Diaphragm Sign
        1. Air below and posterior to the heart results in a continuous line across the diaphragm
      3. Tubular Artery Sign
        1. Major aortic branches highlighted with double line
      4. Ring Around the Artery Sign
        1. Pulmonary artery and main branches highlighted with double line
  2. Chest CT
    1. Small Pneumomediastinum is not uncommon on Trauma chest CT
    2. Consider Chest CT in all suspected cases, to define potential causes

X. Management

  1. Primary Pneumomediastinum (e.g. due to excessive coughing, Asthma)
    1. Often a benign, incidental finding on CT Imaging
    2. Analgesics
    3. Rest
  2. Secondary Pneumomediastinum (e.g. Tracheobronchial Injury, Esophageal Rupture) or increased inflammatory markers
    1. Serious, potentially life threatening finding
    2. Intensive Care Unit Admission and thoracic surgery Consultation

XI. Complications

  1. Tension Pneumomediastinum (rare)
    1. Emergent thoracic surgery Consultation
    2. Presents with Hypotension
    3. Acute stabilization requires suprasternal notch Blunt Dissection (relieves tension)
    4. Avoid worsening intrathoracic pressure
      1. Intubated patients should be allowed permissive hypercapnia to limit airway pressures

XII. References

  1. Dreis (2020) Crit Dec Emerg Med 34(7):3-21
  2. Swadron (2019) Pulmonology 2, CCME Board Review, accessed 6/18/2019

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