What is Pneumoperitoneum?
Pneumoperitoneum is the presence of free air within the peritoneal cavity, which in approximately 90% of cases indicates rupture or perforation of an intra-abdominal viscus requiring urgent surgical intervention. 1, 2
Definition and Clinical Significance
Pneumoperitoneum refers to free air in the peritoneal cavity, distinct from air within the bowel lumen or bowel wall. 1 This radiological finding typically suggests serious intra-abdominal disease requiring urgent surgical management, though approximately 10% of cases have nonsurgical causes that can be managed conservatively. 2, 3
Common Causes
Surgical causes (90% of cases):
- Perforated gastric or duodenal ulcers account for the greatest number of cases 4, 3
- Inflammatory conditions such as peptic ulcer disease or diverticulitis 5
- Traumatic bowel injury 5
- Neoplastic perforation (colon cancer) 6
- Anastomotic leak 5
Nonsurgical causes (10% of cases):
- Postoperative retained air (most common nonsurgical cause) 2, 3
- Thoracic sources (pneumothorax, mechanical ventilation, tracheobronchial rupture) 2, 7
- Gynecologic procedures 2
- Iatrogenic from laparoscopy or colonoscopy 8, 2
- Idiopathic 2
Diagnostic Approach
CT scan with contrast is the first-line diagnostic test, with 93-96% sensitivity and 93-100% specificity for detecting perforation. 1, 9 CT can identify the site of perforation with 95% sensitivity and determine the underlying cause in most cases. 9
Imaging Modalities in Order of Preference:
- CT scan: Most sensitive and specific, can distinguish surgical from nonsurgical causes, identifies perforation site and complications 4, 1, 9
- Plain radiographs: Erect chest/abdomen X-rays detect free air in 30-85% of perforations, with 92% positive predictive value when present 4, 9
- Ultrasound: Can detect free intraperitoneal air but has limited ability to identify perforation site and cause 8, 9
Clinical Presentation
Localized or generalized peritonitis is typical but may be present in only two-thirds of patients with perforated peptic ulcer. 4 Physical examination findings may be equivocal, particularly in patients with contained or sealed perforations. 4
Associated Findings:
- Sudden onset abdominal pain 4
- Leukocytosis, metabolic acidosis, elevated serum amylase 4
- Signs of sepsis or septic shock in severe cases 4
- Hemodynamic instability in tension pneumoperitoneum 6
Management Algorithm
For hemodynamically unstable patients with signs of peritonitis, immediate surgical exploration without delay for additional imaging is required. 1
Stepwise Approach:
Unstable patients with peritonitis:
Stable patients:
Critical Pitfalls to Avoid
Up to 12% of patients with perforations may have a normal CT scan, so clinical suspicion should guide management when imaging is equivocal. 4 In peripheral hospitals without prompt CT access, plain X-ray showing free air combined with clear history and peritoneal signs is sufficient to justify surgical exploration. 4
Conservative management is only warranted in the absence of symptoms and signs of peritonitis. 2 Failure to recognize nonsurgical pneumoperitoneum has led to unnecessary laparotomies with serious postoperative complications in reported cases. 3
Special Consideration - Tension Pneumoperitoneum:
This life-threatening variant causes abdominal compartment syndrome with respiratory and circulatory instability. 6 A perforated bowel wall or surrounding omental fat can act as a one-way valve, creating tension without active air infusion. 6 Immediate needle decompression is required before definitive surgical management. 6