pneumoperitoneum

Pneumoperitoneum is the presence of free gas within the peritoneal cavity. It is most often the radiographic manifestation of perforation of a hollow abdominal viscus, typically requiring urgent evaluation and management. It can also arise after abdominal or thoracic instrumentation, surgery, trauma, or certain medical therapies, and less commonly can occur without an obvious perforation.

Non-surgical pneumoperitoneum refers to cases where no perforation is evident after evaluation. Causes include recent abdominal procedures, mechanical ventilation or other medical interventions, and thoracic sources of air that track into the peritoneal space. Distinguishing surgical from non-surgical pneumoperitoneum is important and relies on clinical assessment and imaging.

Clinical presentation varies with cause. Many patients with perforation present with sudden, severe abdominal pain and signs of peritonitis, sometimes with shock. Others, particularly those with non-perforated or small-volume free air, may have mild or nonspecific symptoms.

Imaging is central to diagnosis. An upright chest radiograph or abdominal radiograph is typically obtained first and may show free air under the diaphragm. The Rigler sign (double-wall sign) can aid interpretation. Computed tomography of the abdomen and pelvis is more sensitive and can help localize a perforation, identify alternative etiologies, and assess associated injuries.

Management depends on the underlying cause. Perforation with peritoneal contamination generally requires emergent surgical intervention. Non-surgical pneumoperitoneum is managed conservatively, focusing on observation and treatment of the underlying cause, with close clinical monitoring. Prognosis correlates with the etiology and the speed of diagnosis and treatment.