Pneumoperitoneum

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Pneumoperitoneum Classification and external resources
Frontal chest X-ray. The air bubble below the right hemidiaphragm (on the left of the image) is a pneumoperitoneum.
ICD-10	K 66.8
ICD-9	568.89, 770.2
DiseasesDB	31511
eMedicine	radio/562
MeSH	D011027

Pneumoperitoneum is air or gas in the abdominal (peritoneal) cavity, often seen on x-ray, but small amounts are often missed and CT is nowadays regarded as a criterion standard in the assessment of a pneumoperitoneum.^[1], CT 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, although any part of the bowel may perforate from a benign ulcer, tumor or trauma. A perforated appendix seldom causes a pneumoperitoneum.

A pneumoperitoneum is deliberately created by the surgical team in order to perform laparoscopic surgery. This is achieved by insufflating the abdomen with carbon dioxide.

[edit] Causes

Perforated peptic ulcer
Bowel obstruction
Ruptured diverticulum
Penetrating trauma
Ruptured inflammatory bowel disease (e.g. megacolon)
Necrotising enterocolitis/Pneumatosis coli^[2]
Bowel Cancer
Ischemic bowel
Steroids
After laparotomy
After laparoscopy
Break down of a surgical anastomosis
Bowel injury after endoscopy
Peritoneal dialysis
Vaginal insufflation (air enters via the fallopian tubes, e.g. water-skiing, oral sex)
Colonic or peritoneal infection
From chest (e.g. bronchopleural fistula)

Subphrenic abscess, bowel interposed between diaphragm and liver (Chilaiditi syndrome), and linear atelectasis at the base of the lungs can simulate free air under the diaphragm on a chest x-ray.