Pneumoperitoneum is air or gas in the abdominal (peritoneal) cavity. It is often seen on X-ray

X-ray

X-radiation is a form of electromagnetic radiation. X-rays have a wavelength in the range of 0.01 to 10 nanometers, corresponding to frequencies in the range 30 petahertz to 30 exahertz and energies in the range 120 eV to 120 keV. They are shorter in wavelength than UV rays and longer than gamma...

, but small amounts are often missed, and CT

Computed tomography

X-ray computed tomography or Computer tomography , is a medical imaging method employing tomography created by computer processing...

 is nowadays regarded as a criterion standard in the assessment of a pneumoperitoneum. CT

Computed tomography

X-ray computed tomography or Computer tomography , is a medical imaging method employing tomography created by computer processing...

 can visualize quantities as small as 5 cm³ of air or gas. The most common cause is a perforated abdominal viscus, generally a perforated peptic ulcer

Peptic ulcer

A peptic ulcer, also known as PUD or peptic ulcer disease, is the most common ulcer of an area of the gastrointestinal tract that is usually acidic and thus extremely painful. It is defined as mucosal erosions equal to or greater than 0.5 cm...

, although any part of the bowel may perforate from a benign ulcer, tumor

Tumor

A tumor or tumour is commonly used as a synonym for a neoplasm that appears enlarged in size. Tumor is not synonymous with cancer...

 or abdominal trauma

Abdominal trauma

Abdominal trauma is an injury to the abdomen. It may be blunt or penetrating and may involve damage to the abdominal organs. Signs and symptoms include abdominal pain, tenderness, rigidity, and bruising of the external abdomen. Abdominal trauma presents a risk of severe blood loss and infection...

. A perforated appendix

Vermiform appendix

The appendix is a blind-ended tube connected to the cecum , from which it develops embryologically. The cecum is a pouchlike structure of the colon...

 seldom causes a pneumoperitoneum.

A pneumoperitoneum is deliberately created by the surgical team in order to perform laparoscopic surgery

Laparoscopic surgery

Laparoscopic surgery, also called minimally invasive surgery , bandaid surgery, or keyhole surgery, is a modern surgical technique in which operations in the abdomen are performed through small incisions as opposed to the larger incisions needed in laparotomy.Keyhole surgery makes use of images...

. This is achieved by insufflating the abdomen with carbon dioxide

Carbon dioxide

Carbon dioxide is a naturally occurring chemical compound composed of two oxygen atoms covalently bonded to a single carbon atom...

.

Causes

• Perforated peptic ulcer
  Peptic ulcer
  A peptic ulcer, also known as PUD or peptic ulcer disease, is the most common ulcer of an area of the gastrointestinal tract that is usually acidic and thus extremely painful. It is defined as mucosal erosions equal to or greater than 0.5 cm...
  
  
• Bowel obstruction
  Bowel obstruction
  Bowel obstruction is a mechanical or functional obstruction of the intestines, preventing the normal transit of the products of digestion. It can occur at any level distal to the duodenum of the small intestine and is a medical emergency...
  
  
• Ruptured diverticulum
  Diverticulum
  A diverticulum is medical or biological term for an outpouching of a hollow structure in the body. Depending upon which layers of the structure are involved, they are described as being either true or false....
  
  
• Penetrating trauma
  Penetrating trauma
  Penetrating trauma is an injury that occurs when an object pierces the skin and enters a tissue of the body, creating an open wound. In blunt, or non-penetrating trauma, there may be an impact, but the skin is not necessarily broken. The penetrating object may remain in the tissues, come back out...
  
  
• Ruptured inflammatory bowel disease
  Inflammatory bowel disease
  In medicine, inflammatory bowel disease is a group of inflammatory conditions of the colon and small intestine. The major types of IBD are Crohn's disease and ulcerative colitis.-Classification:...
  
   (e.g. megacolon
  Megacolon
  Megacolon is an abnormal dilation of the colon . The dilatation is often accompanied by a paralysis of the peristaltic movements of the bowel...
  
  )
• Necrotising enterocolitis/Pneumatosis coli
• Bowel Cancer
• Ischemic bowel
• Steroids
• After laparotomy
  Laparotomy
  A laparotomy is a surgical procedure involving a large incision through the abdominal wall to gain access into the abdominal cavity. It is also known as coeliotomy.- Terminology :...
  
  
• After laparoscopy
  Laparoscopy
  Laparoscopy is an operation performed in the abdomen or pelvis through small incisions with the aid of a camera...
  
  
• Breakdown of a surgical anastomosis
  Surgical anastomosis
  In surgical jargon, to create an anastomosis is to join together two hollow organs , usually to restore continuity after resection, or to bypass an unresectable disease process. Historically such procedures were performed with suture material, but increasingly mechanical staplers and biological...
  
  
• Bowel injury after endoscopy
  Endoscopy
  Endoscopy means looking inside and typically refers to looking inside the body for medical reasons using an endoscope , an instrument used to examine the interior of a hollow organ or cavity of the body. Unlike most other medical imaging devices, endoscopes are inserted directly into the organ...
  
  
• Peritoneal dialysis
  Peritoneal dialysis
  Peritoneal dialysis is a treatment for patients with severe chronic kidney disease. The process uses the patient's peritoneum in the abdomen as a membrane across which fluids and dissolved substances are exchanged from the blood...
  
  
• Vaginal insufflation (air enters via the fallopian tubes, e.g. water-skiing, oral sex)
• Colonic or peritoneal infection
  Infection
  An infection is the colonization of a host organism by parasite species. Infecting parasites seek to use the host's resources to reproduce, often resulting in disease...
  
  
• From chest (e.g. bronchopleural fistula
  Fistula
  In medicine, a fistula is an abnormal connection or passageway between two epithelium-lined organs or vessels that normally do not connect. It is generally a disease condition, but a fistula may be surgically created for therapeutic reasons.-Locations:Fistulas can develop in various parts of the...
  
  )
• Non-invasive PAP (positive airway pressure) can force air down duodenum as well as down trachea.

Differential diagnosis

Subphrenic abscess

Subphrenic abscess

Subphrenic abscess is a disease characterized by an accumulation of infected fluid between the diaphragm, the liver and the spleen. This abscess develops after surgical operations for bowel perforation. It is also associated with peritonitis....

, bowel interposed between diaphragm and liver (Chilaiditi syndrome

Chilaiditi syndrome

Chilaiditi syndrome is a rare condition when pain occurs due to transposition of a loop of large intestine in between the diaphragm and the liver, visible on plain abdominal X-ray or chest X-ray....

), and linear atelectasis

Atelectasis

Atelectasis is defined as the collapse or closure of alveoli resulting in reduced or absent gas exchange. It may affect part or all of one lung. It is a condition where the alveoli are deflated, as distinct from pulmonary consolidation.It is a very common finding in chest x-rays and other...

at the base of the lungs can simulate free air under the diaphragm on a chest X-ray.