What is pneumomediastinum, particularly in young adults or individuals with a history of respiratory issues such as asthma or chronic obstructive pulmonary disease (COPD)?

What is Pneumomediastinum?

Pneumomediastinum is the presence of free air in the mediastinal cavity, which can occur spontaneously or secondary to an underlying cause, and represents a potentially serious complication particularly in patients with respiratory conditions like asthma or COPD. 1

Definition and Pathophysiology

Pneumomediastinum, also known as mediastinal emphysema, occurs when air escapes from the lungs, airways, or bowel into the chest cavity and becomes trapped in the mediastinal space. 2, 3 The condition results from air leaking through damaged alveoli or airways and dissecting along tissue planes into the mediastinum. 3

The condition is classified into two categories:

• Secondary pneumomediastinum: occurs with a clear instigating event or underlying cause 2
• Spontaneous pneumomediastinum (SPM): free air discovered in the mediastinal cavity without a clear etiology 2

Clinical Presentation

Primary Symptoms

• Severe central chest pain is the most common presenting symptom, occurring in almost all patients with SPM 2
• Shortness of breath or labored breathing typical of respiratory system problems 3
• Chest tightness, which may occur even with exertion such as prolonged cycling 4

Physical Examination Findings

• Hamman's crunch: a characteristic "crunching" sound timed with the cardiac cycle on auscultation, though present in only one-fifth of patients 2, 3
• Subcutaneous emphysema (crepitus) specifically affecting the face, neck, and chest 3, 4
• Voice distortion similar to helium inhalation 3

High-Risk Populations

Respiratory Disease Associations

Pneumomediastinum and pneumothorax are the most concerning findings in patients with acute asthma exacerbation, with pneumothorax found to be the direct cause of death in 27% of cases in one series of patients with acute exacerbation. 1 Patients with pre-existing pulmonary diseases show greater propensity for developing free air in the mediastinal cavity. 2

Risk factors include:

• Asthma: particularly during exacerbations or with prolonged physical exertion 1, 4
• COPD: as part of complications from airway disease 1
• COVID-19 infection: emerging as a recognized risk factor 4
• Physical trauma or iatrogenic causes: including post-surgical complications 5

Diagnostic Approach

Imaging Modalities

• Chest radiography: can identify pneumomediastinum by visualizing a radiolucent airline in the mediastinum and/or surrounding the heart 5, 6
• CT chest without IV contrast: provides definitive diagnosis and is superior for detecting the extent and complications 5, 6

Chest radiographs are usually sufficient to diagnose pneumothorax, but CT should be reserved for patients who require additional evaluation of their pneumothorax to look for an underlying cause. 1

Radiographic Signs

Multiple radiographic signs can indicate pneumomediastinum, including pneumopericardium, continuous diaphragm sign, Naclerio's V sign, ring-around-the-artery sign, and thymic spinnaker-sail sign. 6

Clinical Significance and Management

Potential Complications

Pneumomediastinum can lead to:

• Pneumothorax (air in pleural space) 6
• Pneumopericardium (air around the heart) 6
• Cardiac tamponade-like symptoms from increased intrapulmonary pressure on venous flow to the heart 3

Treatment Approach

Most pneumomediastinums are treated conservatively, as the tissues in the mediastinum will slowly resorb the air in the cavity. 3 Patients typically require:

• Hospital admission for observation 4
• Supportive care without surgical intervention in uncomplicated cases 4
• Symptom improvement usually occurs within 24 hours 4
• Surgery (mediastinotomy) is reserved for complicated cases with tension pneumomediastinum 4

Clinical Pitfalls

SPM must be part of the differential diagnosis of any chest pain patient to expedite discovery and management, as it is often misdiagnosed due to the vague nature of presenting symptoms. 2 The absence of Hamman's crunch does not rule out pneumomediastinum, as it is present in only 20% of cases. 2

Distinguishing pneumomediastinum from pneumothorax and pneumopericardium on imaging is essential for appropriate management. 6