Pneumoperitoneum

Pneumoperitoneum is free gas within the peritoneal cavity. Outside the post-operative period it usually means perforation of a hollow viscus — most often a peptic ulcer or a colonic diverticulum.

Clinical presentation

Sudden severe abdominal pain, peritonism and a rigid abdomen. Elderly or immunosuppressed patients and those on steroids may have surprisingly few signs.

Radiographic features

Erect chest radiograph

• A crescent of lucency under one or both hemidiaphragms
• The patient should be upright for several minutes beforehand so gas can rise
• Beware Chilaiditi sign (bowel between liver and diaphragm), which shows haustral folds

Supine abdominal radiograph

• Rigler sign: both sides of the bowel wall are visible
• Falciform ligament sign and the football sign in large collections

CT

The most sensitive test: even a few bubbles of free gas are seen anteriorly on lung windows. CT often shows the site of perforation.

Treatment and prognosis

Resuscitation, antibiotics and urgent surgical review. A small, contained leak may occasionally be managed conservatively.

Practical points

Gas may persist for several days after laparotomy or laparoscopy, so correlate with the surgical history.