E1268. There´s a Gas Leak: Where´s the Culprit?
  1. Ana Costa; Hospital de Braga
  2. Daniela Barros; Hospital de Braga
  3. Carlos Oliveira; Hospital de Braga
  4. Manuela Certo; Hospital de Braga
- To review the wide spectrum of abdominal causes of free gas; - To illustrate the main findings at computed tomography (CT); - To discuss the differential diagnosis.

Educational Goals / Teaching Points
The presence of gas outside of the lumen of the gastrointestinal tract is considered abnormal finding. The spectrum of diseases ranges from infections, inflammatory, iatrogenic, traumatic to malignancies. Free gas is frequently seen at the emergency room and comprises asymptomatic to life-threatening clinical situations. CT is the imaging tool of choice for demonstration of extraluminal gas and mild cases of pneumoperitoneum, as well as to diagnose the underlying cause. Plain radiography and ultrasound are less sensitive.

Key Anatomic/Physiologic Issues and Imaging Findings/Techniques
This pictorial review presents the typical and atypical abdominal causes of free gas, using our archive. We will show abdominal causes of air leakage and demonstrate the most common findings in CT, the imaging tool choice for diagnosis. Mesenteric ischemia presents as a life-threatening event and emergent CT should always be done with contrast acquisition according to the equipment, but generally at 50 seconds to see the mesenteric defect. Additional findings like air in the portal-mesenteric axis or the bile ducts can be depicted. Bowel or gastric trauma is also a possible cause for air leakage, with CT reconstructions being fundamental for exact injury location. Gastric distention can be misleading as the aetiology can be pointed to the bowel. An infectious cause must always be present in the differential diagnosis, either gastrointestinal (GI) or genito-urinary (GU). Emphysematous pyelonephritis and cystitis presents as an ominous cause that can be inferred at ultrasound (US) but demands a CT for final diagnosis. Necrotizing fasciitis, despite not commonly included in the genitourinary causes, can also be a cause of air leakage as shown in our case of colorectal cancer with CT, also as a key element showing asymmetrical retroperitoneal fat stranding and fascial enhancement. GI infectious causes for air leakage present a variety of diagnosis, from hepatic abscess to emphysematous cholecystitis to diverticulitis. In our presentation we intend to demonstrate the importance of CT for diagnosis with clear clues pointed and unequivocal gas demonstration.

The radiologist has a fundamental role in recognition of a gas leak, and a must know for every resident and specialist when there is clinical suspicion because in most causes are life-threatening and an emergent hands-on approach is demanded.