What is Pneumoperitoneum?

Pneumoperitoneum: Definition, Diagnosis, and Management

Pneumoperitoneum is defined as the presence of free air in the peritoneal cavity, most commonly indicating perforation of an intra-abdominal viscus requiring urgent surgical intervention, though approximately 10% of cases have non-surgical causes. 1, 2

Etiology

Pneumoperitoneum can be categorized based on cause:

Surgical Causes (90%)

• Perforated peptic ulcer (most common)
• Perforated colon (intraperitoneal segments like cecum, transverse colon, sigmoid)
• Iatrogenic colonoscopy perforation
• Perforated appendix
• Other hollow viscus perforations

Non-Surgical Causes (10%)

• Post-operative retained air (most common benign cause)
• Thoracic causes (pneumomediastinum, pneumothorax)
• Mechanical ventilation
• Gynecological causes
• Idiopathic causes

Clinical Presentation

Patients with pneumoperitoneum typically present with:

• Sudden onset abdominal pain
• Localized or generalized peritonitis (in about two-thirds of patients)
• Abdominal distension
• Fever
• Rectal bleeding (in some cases)

However, it's important to note that some patients may have minimal or absent peritoneal signs, particularly with contained or sealed leaks 1.

Diagnostic Approach

Laboratory Tests

• White blood cell count (elevated in infection)
• C-reactive protein (elevated in inflammation)
• Pro-calcitonin level (useful for delayed presentation >12 hours) 1

Imaging Studies

1. Plain Radiographs:

   • Upright or left lateral decubitus abdominal/chest X-rays can detect free peritoneal air
   • Positive predictive value of 92% for iatrogenic colonoscopy perforations
   • Higher PPV for diagnostic procedures (100%) than therapeutic procedures (45%)
   • Limited sensitivity (detects pneumoperitoneum in only 30-85% of cases) 1

2. CT Scan:

   • Gold standard for detecting pneumoperitoneum
   • Can detect small amounts of free air and fluid
   • Can often identify the perforation site
   • Can distinguish between intraperitoneal and extraperitoneal air
   • Multi-detector CT (MDCT) is 86% accurate in predicting perforation site 1

3. Ultrasound:

   • May be useful when radiation exposure is a concern (children, pregnant women)
   • Not definitive for excluding pneumoperitoneum 1

4. Additional Techniques:

   • Water-soluble contrast via nasogastric tube can help detect gastroduodenal perforation
   • Double contrast CT (IV and rectal) useful for detecting concealed perforations 1

Management

Management depends on the cause, amount of free air, and patient's clinical condition:

Surgical Management

Immediate surgical exploration is indicated for:

• Patients with peritoneal signs
• Hemodynamic instability
• Fever with signs of sepsis
• Large amount of free air with free fluid on imaging
• Evidence of bowel perforation on imaging 3

Conservative Management

May be considered in highly selected cases:

• Hemodynamically stable patients
• Minimal abdominal tenderness
• Small amount of free air without free fluid
• No evidence of bowel perforation on imaging 3

Conservative management includes:

• NPO (nothing by mouth)
• IV fluids
• Close monitoring of vital signs
• Serial abdominal examinations
• Broad-spectrum antibiotics if infection is suspected 3

Special Considerations

Intraperitoneal vs. Extraperitoneal Perforations

• Perforations of intraperitoneal segments (cecum, transverse colon, sigmoid) lead to free intraperitoneal fluid and air
• Perforations of ascending/descending colon and rectum result mainly in extraperitoneal air
• Mixed situations can occur 1

Idiopathic Pneumoperitoneum

• Rare condition where pneumoperitoneum occurs without identifiable cause
• May be managed conservatively in asymptomatic patients without signs of peritonitis 4

Pitfalls and Caveats

1. Not all pneumoperitoneum requires surgery - approximately 10% of cases have non-surgical causes 5

2. CT scan may be normal in up to 12% of patients with perforations; oral water-soluble contrast may improve diagnostic sensitivity 1

3. Pneumatosis intestinalis with pneumoperitoneum can mimic bowel ischemia with perforation, potentially leading to non-therapeutic laparotomy 6

4. Consider gynecological causes in female patients, such as perforated pyometra, which can present with peritonitis and pneumoperitoneum 7

5. Delayed intervention in patients with signs of peritonitis or sepsis can result in increased morbidity and mortality 3