What is a pneumoperitoneum?

What is a Pneumoperitoneum?

Pneumoperitoneum is the presence of free air within the peritoneal cavity, most commonly indicating visceral perforation requiring urgent surgical intervention, though approximately 10% of cases occur without organ perforation and may be managed conservatively. 1, 2

Definition and Clinical Significance

Pneumoperitoneum refers to free intraperitoneal gas detected radiologically, typically seen as air under the diaphragm on imaging studies. 1, 3 This finding carries critical diagnostic implications:

• In approximately 90% of cases, pneumoperitoneum indicates rupture of an intra-abdominal viscus requiring surgical exploration, with perforated gastric and duodenal ulcers accounting for the majority of these perforations. 2, 4

• The remaining 10% of cases represent "spontaneous" or "non-surgical" pneumoperitoneum, where free air occurs without organ perforation and can often be managed with supportive measures alone. 3, 4

Common Causes

Surgical Pneumoperitoneum (Requiring Intervention)

The most frequent pathological sources include:

• Perforated peptic ulcers (gastroduodenal region most common) 2
• Perforated diverticulitis with generalized peritonitis 5
• Perforated appendicitis 5
• Colonic perforations (non-diverticular) 5
• Small bowel perforations from trauma, ischemia, or inflammatory conditions 5
• Post-operative anastomotic leaks 2

Non-Surgical Pneumoperitoneum (May Not Require Surgery)

• Iatrogenic causes: Most commonly post-laparotomy or post-laparoscopy air that typically resolves within one week 4
• Thoracic sources: Air tracking from the chest cavity through the diaphragm 4
• Gastrointestinal tract: Mucosal injury during colonoscopy where air dissects into the bowel wall through mucosal defects 6
• Gynecologic sources 4
• Idiopathic spontaneous pneumoperitoneum: Extremely rare cases with no identifiable cause 1, 7

Diagnostic Approach

Imaging Modalities

Contrast-enhanced CT scan is the preferred imaging modality because it provides high sensitivity for locating perforation sites, delineating contamination, and detecting complications such as abscess formation. 5, 8

• CT scan specificity: Free intraperitoneal air has 99% specificity for bowel injury requiring surgical treatment 5
• Plain radiographs can detect pneumoperitoneum but miss 15-70% of perforations and cannot characterize the source of free air, severely limiting their utility 8
• Highly specific CT findings warranting immediate surgery include extraluminal air, extraluminal oral contrast, or bowel wall defects 5

Clinical Assessment

Critical elements to evaluate include:

• Signs of peritonitis: Diffuse abdominal tenderness, guarding, rigidity, and rebound tenderness indicate a surgical emergency 8
• Hemodynamic status: Instability (hypotension, tachycardia) mandates immediate surgical exploration 5, 8
• Systemic inflammatory response: Fever, tachycardia, altered mental status 8
• Laboratory markers: White blood cell count, lactate, C-reactive protein, and procalcitonin to assess inflammation and potential sepsis 8, 6

Management Algorithm

Immediate Surgical Exploration Required

Any patient with hemodynamic instability or clinical signs of peritonitis must proceed directly to emergency surgical exploration without awaiting further imaging. 8

This includes:

• Hemodynamically unstable patients regardless of imaging findings 8
• Patients with diffuse peritonitis (guarding, rigidity, rebound tenderness) 8
• CT findings of distant free air with large amounts of intraperitoneal air or distant retroperitoneal air, even without clinical generalized peritonitis (57-60% failure rate with conservative management) 5
• Extraluminal oral contrast or bowel wall defects on CT 5

Immediate interventions include:

• Aggressive fluid resuscitation to restore circulatory volume 8
• Broad-spectrum intravenous antibiotics covering intra-abdominal pathogens 5, 8
• Emergent surgical consultation 8

Conservative (Non-Operative) Management Criteria

Conservative management may be considered ONLY in hemodynamically stable patients without peritonitis who meet ALL of the following criteria: 8

• Localized abdominal pain (no diffuse tenderness)
• Absence of fever
• Stable vital signs (normotensive, normal heart rate)
• Minimal free fluid on imaging
• Suspected small, sealed-off perforation (e.g., post-therapeutic colonoscopy with adequate bowel preparation)

Conservative management protocol when selected: 8

• Serial clinical examinations and repeat imaging every 3-6 hours to detect early deterioration
• Absolute bowel rest (NPO)
• Intravenous fluid hydration
• Broad-spectrum intravenous antibiotics
• Close multidisciplinary follow-up

Special Populations Requiring Surgery

Even with minimal symptoms, the following groups should be managed surgically: 8

• Immunosuppressed individuals
• Organ transplant recipients
• Patients with concurrent colonic disease necessitating operative treatment

Critical Pitfalls to Avoid

The mere presence of subdiaphragmatic free air does NOT automatically mandate urgent surgery—management must be guided by the patient's clinical status. 8 However, several dangerous pitfalls exist:

• Delayed surgery after failed conservative treatment is associated with higher complication rates and longer hospital stays compared with immediate operative management 8
• Early success with conservative therapy does not preclude the later need for operative intervention if the patient's condition worsens 8
• Postponed operative intervention can exacerbate peritonitis and bowel wall inflammation, often requiring more extensive surgery and resulting in poorer prognosis 8
• Lack of clinical awareness about non-surgical pneumoperitoneum is a source of needless laparotomies that can lead to serious postoperative complications 4

If the patient develops clinical deterioration, sepsis, or overt peritonitis during conservative management, surgery must be undertaken without further delay. 8

Specific Clinical Scenarios

Diverticulitis with Pneumoperitoneum

• CT findings of distant free air (a known predictor of failure of non-operative treatment) does not necessarily obligate a surgical approach in hemodynamically stable patients 5
• Non-operative treatment is feasible only for hemodynamically stable patients with CT findings of pericolic extraluminal air or only a small amount of distant intraperitoneal air in the absence of clinical diffuse peritonitis or fluid in the fossa of Douglas 5
• Large amounts of distant intraperitoneal air or distant retroperitoneal air carry a 57-60% failure rate with conservative management 5

Post-Procedural Pneumoperitoneum

• Iatrogenic post-surgical free air typically resolves within the first week after laparotomy or laparoscopic procedures and does not require intervention 4
• Post-colonoscopy pneumoperitoneum may occur when mucosal injury and intraluminal pressure dissect air into the bowel wall, and can sometimes be managed conservatively in stable patients 6