Pneumomediastinum pathophysiology

The pathophysiology of spontaneous pneumomediastinum is based on the existence of a pressure gradient between the alveoli and lung interstitium. Pneumomediastinum occurs when pressure rises in the lungs and causes the air sacs (alveoli) to rupture. Sudden increase in intrathoracic pressure due to a specific triggering event such as Valsalva maneuver, vomiting, asthma exacerbation, physical activity may lead to alveolar rupture and the consequent escape of air into the interstitium. Once the air is in the lung interstitium, it flows towards the hilum and the mediastinum along a pressure gradient between the pleural cavity and the mediastinum. Spontaneous neonatal pneumomediastinum may follow gas trapping associated with the aspiration of blood or meconium, neonatal respiratory distress syndrome, pneumonia, or the use of mechanical ventilation. Another possible mechanism is traumatic damage to the lungs or other nearby structures that allows air to leak into the center of the chest.

For information on anatomy of mediastinum, click here.

• The pathophysiology of spontaneous pneumomediastinum is based on the existence of a pressure gradient between the alveoli and lung interstitium.^[1][2]
• Sudden increase in intrathoracic pressure due to a specific triggering event such as Valsalva maneuver, vomiting, asthma exacerbation, physical activity may lead to alveolar rupture and the consequent escape of air into the interstitium.
• Once the air is in the lung interstitium it flows towards the hilum and the mediastinum along a pressure gradient between the pleural cavity and the mediastinum.^[1]
• Predisposing factors of spontaneous pneumomediastinum are tobacco smoking, use of recreational drugs, past medical history of asthma, pneumonia, COPD and interstitial lung disease.^[3][4][5][6]
• One of the most common scenario of spontaneous pneumomediastinum is the absence of any specific trigger.
• The other precipitating factors are physical exercise, vomiting, cough, infection of the upper airways, inhalation of varnish fumes, rapid ascent or descent phase during dive or hyperbaric treatment.^[7]

• Spontaneous neonatal pneumomediastinum is associated with the aspiration of blood or meconium and birth-related trauma and it is more frequent in post-term newborns.^[8]
• Spontaneous neonatal pneumomediastinum may follow gas trapping associated with the neonatal respiratory distress syndrome, pneumonia, or the use of mechanical ventilation.^[9]

• Secondary pneumomediastinum develops as a consequence of a distinct underlying pathology or chest/abdominal injury, resulting in the intrathoracic dissection of air through the mediastinal planes.^[10]
• Iatrogenic secondary pneumomediastinum may result from recent interventions in the tracheobronchial tree or GI tract such as endoscopies, intubation/extubation, surgical intervention such as thyroidectomy, tracheostomy.
• Secondary pneumomediastinum may also result from blunt or penetrating trauma, ventilator-induced barotrauma, mediastinitis, foreign body in aerodigestive tract, chest cavitary abnormalities, pneumocystis jirovecii pneumonia, Boerhaave syndrome, and amiodarone-induced pulmonary toxicity.

There is no genetics found to be associated with pneumomediastinum.

Conditions associated with spontaneous pneumomediastinum include:^[11]

• Broncial asthma
• COPD
• ARDS
• Boerhaave syndrome
• Interstitial lung disease (rare)
• Connective tissue disease (rare)^[12]
• Dermatomyocitis^[13]
• Tobacco smoking
• Recreational drug use

There are no gross pathological features characteristic for pneumomediastinum.

There are no microscopic histopathological features characteristic for pneumomediastinum.

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