Pneumatosis intestinalis is a sign on x-ray which is highly suggestive for necrotizing enterocolitis. The literal meaning is gas in the bowel wall, as opposed to in the lumen which is normal. Pneumatosis intestinalis (PI) is defined as the presence of gas in the bowel wall. PI is associated with numerous conditions, ranging from benign to life threatening.

There are two theories on pathogenesis of pneumatois intestinalis. Mechanical theory suggests that gas dissects into the bowel wall from either the intestinal lumen or the lungs via the mediastinum due to some mechanism causing increased pressure. Bacterial theory proposes that gas-forming bacilli enter the submucosa through mucosal rents or increased mucosal permeability and produce gas within the bowel wall.