What is the most common cause of intussusception in an adult?

The most common cause of intussusception in adults is neoplasm. Intussusception occurs when a segment of the intestine folds into an adjacent segment, creating a blockage and potentially leading to ischemia if not treated. In adults, this condition is often secondary to underlying structural abnormalities rather than being idiopathic as frequently seen in children.

Neoplasms, particularly benign tumors such as adenomas or malignant tumors like colorectal cancer, serve as the leading precipitating factor in adult cases of intussusception. These growths can create a lead point, causing a segment of the intestine to telescopically slide into another segment.

While viral infections and inflammatory bowel disease can contribute to gastrointestinal issues, they are not the primary causes of intussusception in adults. Diverticulitis can lead to complications in the lower gastrointestinal tract but is not commonly associated with intussusception. Thus, neoplasm is correctly identified as the most frequent cause due to its direct role in creating an anatomical condition that allows intussusception to occur in the adult patient population.