What is Pneumoperitoneum?
Pneumoperitoneum is the presence of free air in the peritoneal cavity, most commonly indicating visceral perforation requiring urgent surgical intervention, though it can occasionally occur without perforation (termed "non-surgical" or "spontaneous" pneumoperitoneum). 1, 2
Definition and Clinical Significance
Pneumoperitoneum represents free intraperitoneal gas that typically results from rupture of a hollow viscus including the stomach, small bowel, and intraperitoneal portions of the colon. 3 When associated with visceral perforation and peritoneal contamination, it produces peritonitis that mandates surgical intervention—this is termed "surgical pneumoperitoneum." 2
Key Distinguishing Features:
- Surgical pneumoperitoneum: Air leak with visceral contents contaminating the peritoneal cavity, producing peritonitis requiring surgery 2
- Non-surgical pneumoperitoneum: Presence of free air with intact bowel, managed conservatively 2, 4, 5
Common Etiologies
The underlying causes of pneumoperitoneum include:
- Inflammatory conditions: Peptic ulcer disease and diverticulitis are responsible for the vast majority of perforations 2
- Traumatic injury: Blunt or penetrating abdominal trauma 6
- Iatrogenic causes: Post-colonoscopy perforation 6
- Neoplasia: Tumor-related perforations 2
- Anastomotic leak: Post-surgical complications 2
- Vascular causes: Ischemic bowel 2
Anatomical Distribution
Perforations of intraperitoneal segments (cecum, transverse colon, sigmoid colon) typically lead to free intraperitoneal fluid and air, whereas perforations of the ascending and descending colon and rectum result mainly in extraperitoneal air. 6
The gastroduodenal region is the most common anatomical site of perforation, accounting for approximately 29% of exploratory laparotomy cases with documented pneumoperitoneum. 2
Clinical Presentation
Patients typically present with:
- Sudden onset abdominal pain 6
- Localized or generalized peritonitis (present in two-thirds of patients with perforated peptic ulcer) 6
- Abdominal tenderness, distension, or guarding 6
- Fever and signs of sepsis 6
Important caveat: Physical examination findings may be equivocal and peritonitis may be minimal or absent, particularly in patients with contained or sealed perforations. 6
Diagnostic Approach
Laboratory Findings:
- White blood cell count and C-reactive protein are the minimum biochemical markers that should be requested 6
- Leukocytosis, metabolic acidosis, and elevated serum amylase are commonly associated with perforation 6
- Procalcitonin levels can be useful in delayed presentations 6, 1
Imaging Modalities:
Plain radiographs can detect pneumoperitoneum with a positive predictive value of 92% for iatrogenic colonoscopy perforations, though sensitivity varies (30-85% detection rate). 6
CT scan with contrast enhancement is the gold standard, providing superior sensitivity and specificity compared to plain radiographs. 6, 1 CT can:
- Detect small amounts of free intraperitoneal air and fluid 6
- Determine the cause and site of perforation 1
- Identify complications such as abscess formation 1
- Distinguish between surgical and non-surgical causes 1
Highly specific CT findings include: extraluminal air, extraluminal oral contrast, bowel wall defects, oral contrast extravasation, and bowel wall discontinuity. 6, 1
Management Implications
For hemodynamically unstable patients with signs of peritonitis, immediate surgical exploration without delay for additional imaging is required. 1, 7 Every hour of delay from admission to surgery is associated with a 2.4% decreased probability of survival. 7
For hemodynamically stable patients without diffuse peritonitis, contrast-enhanced CT scan should be performed to determine the cause and site of perforation before deciding on operative versus conservative management. 1, 7