Imaging Assessment of Ectopic Gas Collections.

Ectopic gas is defined as the presence of gas in abnormal locations, that is, outside the aerodigestive tract. It constitutes a common radiologic finding associated with a wide range of disorders. Although it is usually an innocuous and self-limited condition, it should prompt a search for the underlying cause, given that the clinical significance of ectopic gas varies from benign to life threatening, depending on the site involved and the rate of accumulation. To ensure optimal management of each case, the origin of ectopic gas should be determined. The search for its exact location and underlying cause often represents a challenge, as air can be depicted distant from its point of origin because of fascial interconnectivity. Thorough knowledge of anatomic compartments facilitates quick identification of the cause and contributes to a prompt diagnosis. Likewise, radiologists should be familiar with the alarm signs associated with severe conditions. Imaging studies are essential to help the radiologist confirm the diagnosis of ectopic gas, determine its precise location and extension, identify severe cases, exclude associated complications, and monitor evolution. CT is the modality of choice in the imaging assessment of ectopic gas. In this review, the authors discuss the different causes of ectopic gas with an etiopathogenic approach to describe the myriad processes that might give rise to this condition. In addition, alarm signs associated with potentially fatal ectopic gas are described and depicted. ©RSNA, 2020.