Pneumomediastinum is air in the center of the chest (the mediastinum).

The mediastinum sits between the lungs. It contains the heart, thymus gland, and part of the esophagus and trachea. Air can become trapped in this area.

Air can get into the mediastinum from an injury, or from leakage in the lungs, trachea, or esophagus. Spontaneous pneumomediastinum (SPM) is a form of the condition that doesn’t have an obvious cause.

Pneumomediastinum can happen when pressure rises in the lungs and causes the air sacs (alveoli) to rupture. Another possible cause is damage to the lungs or other nearby structures that allow air to leak into the center of the chest.

Causes of pneumomediastinum include:

  • an injury to the chest
  • surgery to the neck, chest, or upper belly
  • a tear in the esophagus or lungs from an injury or surgical procedure
  • activities that put pressure on the lungs, such as intense exercise or childbirth
  • a rapid change in air pressure (barotrauma), such as from rising very quickly while scuba diving
  • conditions that cause intense coughing, such as asthma or lung infections
  • use of a breathing machine
  • use of inhaled drugs, such as cocaine or marijuana
  • chest infections like tuberculosis
  • diseases that cause lung scarring (interstitial lung disease)
  • vomiting
  • the Valsalva maneuver (blowing hard while you’re bearing down, a technique used to pop your ears)

This condition is very rare. It affects between 1 in 7,000 and 1 in 45,000 of people who are admitted to the hospital. One baby out of every 100,000 is born with it.

Babies and children are more likely to get pneumomediastinum than adults. This is because the tissues in their chest are looser and can allow air to leak.

Other risk factors include:

  • Gender. Men make up most cases (76%), especially men in their 20s to 40s.
  • Lung disease. Pneumomediastinum is more common in people with asthma and other lung diseases.

The main symptom of pneumomediastinum is chest pain. This can come on suddenly and may be severe. Other symptoms include:

  • shortness of breath
  • difficult or shallow breathing
  • coughing
  • neck pain
  • vomiting
  • trouble swallowing
  • a nasal or hoarse voice
  • air under the skin of the chest (subcutaneous emphysema)

Your doctor might hear a crunching sound in time with your heartbeat when listening to your chest with a stethoscope. This is called Hamman’s sign.

Two imaging tests are used to diagnose this condition:

  • Computed tomography (CT). This test uses X-rays to create detailed pictures of your lungs. It can show whether air is in the mediastinum.
  • X-ray. This imaging test uses small doses of radiation to make pictures of your lungs. It can help find the cause of the air leak.

These tests can check for a tear in your esophagus or lungs:

  • Esophagogram is an X-ray of the esophagus that’s taken after you swallow barium.
  • Esophagoscopy passes a tube down your mouth or nose to view your esophagus.
  • Bronchoscopy inserts a thin, lighted tube called a bronchoscope into your nose or mouth to examine your airways.

Pneumomediastinum usually isn’t serious. The air will eventually reabsorb into your body. The main goal in treating it is to manage your symptoms.

Most people will stay overnight in the hospital for monitoring. After that, treatment consists of:

  • bed rest
  • pain relievers
  • anti-anxiety drugs
  • cough medicine
  • antibiotics, if an infection is involved

Some people may need oxygen to help them breathe. Oxygen can also speed the reabsorption of air in the mediastinum.

Any condition that might have caused the air buildup, such as asthma or a lung infection, will need to be treated.

Pneumomediastinum sometimes happens together with pneumothorax. A pneumothorax is a collapsed lung caused by the buildup of air between the lungs and chest wall. People with pneumothorax may need a chest tube to help drain the air.

This condition is rare in babies, affecting only 0.1% of all newborns. Doctors believe it’s caused by a difference in pressure between the air sacs (the alveoli) and the tissues around them. Air leaks from the alveoli and gets into the mediastinum.

Pneumomediastinum is more common in babies who:

  • are on a mechanical ventilator to help them breathe
  • breathe in (aspirate) their first bowel movement (meconium)
  • have pneumonia or another lung infection

Some babies with this condition have no symptoms. Others have symptoms of breathing distress, including:

  • abnormally fast breathing
  • grunting
  • flaring of the nostrils

Babies who have symptoms will get oxygen to help them breathe. If an infection caused the condition, it will be treated with antibiotics. Babies are carefully monitored afterward to make sure the air dissipates.

Although symptoms like chest pain and shortness of breath can be frightening, pneumomediastinum usually isn’t serious. Spontaneous pneumomediastinum often improves on its own.

Once the condition goes away, it usually doesn’t come back. However, it can last longer or return if it’s caused by a repeated behavior (such as drug use) or an illness (like asthma). In these cases, the outlook depends on the cause.