How is gallstone ileus characterized in small bowel obstruction cases?

Gallstone ileus is characterized by the presence of air in the biliary tree, which occurs due to the communication between the gastrointestinal tract and the biliary system that results from a gallstone eroding through the wall of the intestine. This interaction allows air to enter the biliary system, which can be visualized on imaging studies such as X-rays or CT scans. The presence of air in the biliary tree, also known as pneumobilia, is a significant diagnostic clue for gallstone ileus.

In gallstone ileus, small bowel obstruction occurs when a gallstone travels through the bowel and becomes lodged in the intestinal lumen. While the condition is more common in elderly patients due to the demographic's higher incidence of gallstones and related complications, it is not exclusive to this age group. Additionally, while large gallstones are often responsible for the obstruction, smaller stones can also contribute to the condition. The fixed obstruction and the need for gallbladder removal do not directly characterize gallstone ileus, as management may involve surgery but does not always necessitate cholecystectomy in the acute setting.