Intra-abdominal Free Air: Diagnostic Challenges and Critical Differentiators

Intra-abdominal free air is a critical radiologic finding that commonly indicates hollow viscus perforation. Prompt recognition of this finding on plain radiography and computed tomography (CT), 2 of the most commonly used modalities in the setting of suspected hollow viscus perforation, is thus crucial for timely surgical intervention. Diagnosing intra-abdominal free air can be challenging, as it may result from a wide range of both pathologic and benign etiologies. Common pathologic causes include perforation due to peptic ulcer disease (PUD) and diverticulitis and common benign causes include iatrogenic sources such as recent surgery and peritoneal dialysis. Intrinsic limitations of various imaging modalities as well as the condition of the patient also complicate the detection of intra-abdominal free air. As such, it is important to not only detect free air on imaging but to also contextualize it, which can help differentiate surgical from non-surgical causes and guide appropriate management. The goals of this review are to highlight the many causes of free air and the utility of various imaging modalities in its diagnosis, to provide clues to differentiate benign versus surgical etiologies of free air, to suggest a management framework, and to review emerging techniques and future directions in free air detection.