Free Air Under The Diaphragm

Free air under the diaphragm means there is gas under the diaphragms on an X-ray.  The diaphragm is the major muscle of respiration and is located under the lungs.   Gas under the diaphragms is abnormal and can mean that a life threatening condition exists.

What is free air under the diaphragm mean?

Free air under the diaphragms means that there is air under the diaphragm either on an upright chest X-ray or abdominal X-ray. This most frequently indicates free air in the peritoneal or abdominal cavity and can mean that a life threatening condition exists.

Free air under the diaphragms can mean disruption of the wall of the bowel. The air then escapes the bowel and rises underneath the diaphragm on an X-ray that is taken with the patient upright.

What causes free air under the diaphragm?

There are many causes of air under the diaphragms, many of which can be life threatening and some which are benign. Some of the most common causes I see in practice include diverticulitis. This is an inflamed out pouching of the colon which perforated.

Peptic ulcer can cause a perforation of the stomach and free air under the diaphragm.

Sometimes patients after a colonoscopy who have had a perforation can have this finding.

More benign cause is common in post operative patients. This is air that is introduced into the peritoneal cavity during surgery rather then from a perforation of the bowel.

Air introduced from a dialysis catheter in the abdomen can also cause free air.

Sometimes air can dissect from the chest when a patient has abnormal air collections such as pneumothorax or pneumomediastinum.

Symptoms of free air under the diaphragm

The symptoms will depend on the cause of the free air.  A patient with free air under the diaphragm and perforation of bowel will often have abdominal pain and will be sick.

Gas extending from the chest to the abdominal cavity may have symptoms related to the chest.

Benign causes of free air like a catheter in the abdomen may have no symptoms.

How is free air under the diaphragm diagnosed?

Free air under the diaphragm is usually diagnosed with upright X-rays like a chest or abdominal X-ray.  The X-ray has to be upright because the air must rise under the diaphragms.  CT scans can provide additional information regarding the cause of the free air.

What does free air under the diaphragms look like on X-rays?

Free air under the diaphragms looks like dark gas under the diaphragms. The diaphragms separate the chest from the abdominal cavity.  This can be a subtle finding with barely visible gas all the way to massive amounts of gas.

What else can look like free air in radiology?

There are many findings in X-rays which can lead to a false appearance of free air under the diaphragms.  Some of these can include gas filled bowel under the diaphragm.  Fat under the diaphragm.  Gas in skin folds.  Areas of atelectasis or lung collapse mimicking free air.

Can we always tell the cause of the free air from imaging?

No.  Sometimes we do not know the cause.  Sometimes we do not know until after the patient goes to surgery.

Imaging does often identify the cause.  We can see collections of gas concentrated or extending from the site of bowel perforation.

Is free air under the diaphragm dangerous?

It can be when the bowel perforates.   Many of these conditions can be life threatening and require urgent treatment.

What type of doctor treats free air under the diaphragm?

A surgeon becomes involved when there is suspicion of bowel perforation.  Bowel perforation can happen as a result of many causes like: diverticulitis, ischemic bowel, cancer, and mechanical perforation.

Treatment for free air under the diaphragm

Treatment will depend on the cause.  Bowel perforations will often be treated by a surgeon. A surgeon will often be consulted who may choose to take the patient to the operating room.   Treatment will be directed at the underlying cause in the chest when air dissects into the abdomen.  Benign causes will not be treated.

Free air under the diaphragm: summary

Free air under the diaphragm is diagnosed on upright X-rays.  We see gas under the diaphragm.  Free air under the diaphragm is important to diagnose promptly as this can indicate a dangerous bowel perforation.  There are however many benign cause of free air under the diaphragms and mimickers on X-rays.

Often CT is done to try to identify the cause of the free air.  A surgeon will often get involved when there is suspicioun for a bowel perforation.