A bowel obstruction can be caused by tumors, twisting or narrowing of the intestines, or scar tissue, these are called mechanical obstructions. Obstructions can also occur because of inflammation or infection or as a side effect of certain medicines. These are called non-mechanical obstructions and are not included in this topic. In the small intestine, obstructions are most often caused by scar tissue (adhesions). Other causes include hernias, Crohn's disease, and cancer. A blockage can also occur if one part of the intestine folds like a telescope into another part, which is called intussusceptions. In the large intestine, obstructions are most often caused by cancer. Other causes are severe constipation from a hard mass of stool and twisting or narrowing of the intestine that may occur because of diverticulitis or inflammatory bowel disease.