Small bowel obstruction occurs when the small intestine becomes blocked, either from within the bowel itself or from an external source, thus preventing food, liquid and gas from passing adequately through the intestinal tract. Patients present with vomiting, abdominal pain and constipation. The blockage can be either partial or complete. Complete small bowel obstructions are more serious, because the blood flow to the intestine becomes compromised, potentially leading to bowel gangrene.
Adhesions
The most common cause of small bowel obstruction is scar tissue, called adhesions, from previous abdominal operations. It accounts for almost 60 percent of small intestine obstruction. Scar tissue forms bands in the abdominal cavity. A loop of the small intestine can slip underneath one of these bands, forming a noose-like trap around the intestine. The bowel becomes blocked and can eventually become gangrenous, either from the pressure of fluid backup or at the point of the band. Operations that commonly cause adhesions are appendectomy, colon resection and gynecological procedures like hysterectomy.
Hernias
Hernias are the second most common cause of small bowel obstruction and the most common cause in patients who have not had prior surgery. A hernia is an abnormal opening in the wall of a cavity, allowing tissue to pass through where it should not. The most common hernia and the one that commonly causes small bowel obstruction is the inguinal hernia, in which the groin muscles weaken and allow a loop of small intestine to pass through from the abdomen. The intestinal loop moves out of the hernia but cannot always slide back into the abdominal cavity. This loop can then become kinked, preventing passage of material and causing the bowel obstruction.
Tumors
Tumors represent another cause of small bowel obstruction. The tumor may originate from within the small bowel itself and prevent the passage of any intestinal contents. However, primary small bowel tumors arise very rarely, representing only 1 to 5 percent of all tumors of the gastrointestinal tract. More likely, a more common tumor from another organ in the abdominal cavity, like colon or ovary, will grow and push on the small bowel, causing the bowel to kink and block off. Metastasis from other, more distant tumors, such as lung or melanoma, can grow on the outer surface of the small intestine. This can either kink the bowel from the outside or grow into the small intestine and block it as a primary small bowel tumor would.
