Pneumomediastinum is a medical condition defined by the presence of air or gas within the mediastinum, the central compartment of the chest cavity. This space is situated between the two lungs and contains the heart, major blood vessels, the trachea, and the esophagus. The presence of air in this area is also referred to as mediastinal emphysema. While the word “pneumomediastinum” may sound alarming, the condition is typically rare and often resolves on its own. Most cases are self-limited, meaning the body naturally reabsorbs the trapped air over time.
How Air Enters the Mediastinum
The mechanism by which air escapes into the central chest space is most often explained by the Macklin effect, a three-step pathophysiological process. This process begins when a sudden, high pressure inside the small air sacs of the lungs, called alveoli, causes them to rupture. The released air then travels along the peribronchovascular sheaths—the connective tissue surrounding the bronchi and blood vessels—tracking into the mediastinum.
This sudden increase in pressure, known as barotrauma, can be triggered by forceful straining or respiratory effort. Common causes include severe coughing, intense vomiting, or the straining associated with a difficult childbirth. Exacerbations of underlying respiratory conditions like asthma or chronic obstructive pulmonary disease (COPD) are also common factors. Other triggers include intense physical straining, such as heavy weightlifting, the inhalation of certain recreational drugs, or blunt trauma to the chest.
Recognizing the Signs and Confirmation
The most frequent symptom is a sharp pain in the chest, often located behind the breastbone. This discomfort may radiate upward into the neck or down the arms. The pain is typically aggravated by deep breathing or swallowing.
A physical examination may reveal subcutaneous emphysema, which is the sensation of crackling or air bubbles under the skin, usually felt in the neck or upper chest. A medical professional may also listen for Hamman’s sign, a distinct crunching or rasping sound heard with a stethoscope over the heart. While this sound is considered pathognomonic, meaning highly characteristic of the condition, it is only present in a minority of patients.
Diagnosis is typically confirmed quickly and non-invasively through imaging. A standard chest X-ray frequently shows air outlining the structures in the mediastinum. If the X-ray is inconclusive, a Computed Tomography (CT) scan may be performed. The CT scan provides a detailed, cross-sectional view, allowing for a better assessment of the extent of the trapped air and helping to rule out other serious underlying issues.
Treatment and Recovery Expectations
Management of pneumomediastinum, particularly in spontaneous cases, is overwhelmingly conservative. The primary goal is supportive care, allowing the body to naturally reabsorb the free air. This typically involves sufficient rest and the administration of pain medication, often using Nonsteroidal anti-inflammatory drugs (NSAIDs) for chest or neck discomfort.
Supplemental oxygen is sometimes provided through a face mask or nasal cannula. Breathing higher concentrations of oxygen helps speed up air reabsorption by creating a pressure gradient that encourages the trapped nitrogen gas to diffuse back into the bloodstream. The patient is usually kept under observation for 24 to 48 hours to monitor for complications.
The prognosis for spontaneous pneumomediastinum is excellent, with most patients experiencing a full recovery. The trapped air generally resolves within a few days to a week. Hospital stays are typically short. Addressing the underlying cause, such as managing an asthma exacerbation or suppressing severe coughing, is important to prevent recurrence.
Understanding Rare Complications
Although the condition is generally mild, air trapping can rarely lead to severe outcomes. The most serious complication is tension pneumomediastinum. This occurs when air accumulates under pressure, compressing the great vessels and the heart. This compression impairs blood return, leading to low blood pressure and reduced oxygen levels.
The air can also spread along tissue planes to other parts of the body, resulting in pneumopericardium (air surrounding the heart) or pneumorrhachis (air extending into the epidural space of the spine). Surgical intervention is almost never necessary for spontaneous pneumomediastinum. However, if the underlying cause involves a tear in the esophagus or a major bronchus, or if tension pneumomediastinum develops, aggressive measures, including surgical decompression, may be required.