Adhesions are the most common cause of small-bowel obstruction in U.S. adults. Most adhesions result from previous abdominal operations or inflammatory processes, although isolated congenital adhesions can occur as well.
Incarcerated hernias are the second-most-common cause of small-bowel obstructions in industrialized nations. They are the most common cause of SBO worldwide. In industrialized nations, they are the most common cause of SBO in children and in patients without prior abdominal surgery.
Intussusception occurs when one portion of bowel (the intussusceptum) telescopes into another (the intussuscipiens). Tumors, polyps, enlarged mesenteric lymph nodes, or even a Meckel diverticulum may serve as lead points of the telescoped segment. Unlike in children, intussusception in an adult should always prompt a workup for bowel pathology.
Volvulus is often caused by adhesions or congenital anomalies such as intestinal malrotation. It more commonly occurs in the colon.
Strictures secondary to ischemia, inflammation (Crohn disease), radiation therapy, or prior surgery may cause obstruction.
Gallstone ileus occurs as a complication of cholecystitis. Fistulization between the biliary tree and the small bowel allows gallstones to travel distally and become lodged, typically at the ileocecal valve.
External compression from tumors, abscesses, hematomas, or other masses can cause functional SBO.
Foreign bodies typically pass without incident. Items presenting with obstruction may require operation if they cannot be retrieved endoscopically. Pathology due to swallowing foreign bodies is more common in institutionalized patients.