A bowel obstruction is a partial or complete blockage of the intestines that prevents the normal passage of substances, including gas and food (both fluid and solid), through the intestines. When blockage occurs in the small intestine, it is called small intestine obstruction and when it occurs in the large intestine, it is referred to as large intestine or colonic obstruction.

When food is consumed, it enters the mouth and travels through the esophagus, stomach, small intestine and finally the large intestine, before waste (stool) is expelled through the anus. A patient with a bowel obstruction is unable to defecate properly. The urge to defecate is typically present, but something is blocking the stool from exiting the body.

The small intestine is composed of the duodenum, jejunum and ileum. Obstruction of this organ most commonly occurs in the top and middle sections, the duodenum and jejunum. Obstruction can occur in all three sections of the large intestine (the cecum, colon and rectum).

When a bowel obstruction occurs, the part of the intestine above the obstruction continues to function. The intestine then enlarges as it fills up with food, fluid, digestive secretions and gas, causing its lining to become swollen and inflamed. Stool is unable to move through and becomes trapped. Bowel obstructions may be partial or complete.

Intestinal pseudo obstruction is a condition that causes similar symptoms, but upon examination no obstruction can be found. It is caused by a problem in the muscles or nerves of the intestines, and may result from disease (e.g., Parkinson’s disease) or the use of certain medications (e.g., narcotic pain relievers, antidepressants).

Bowel obstructions may occur during the advanced stages of cancer. The most common cancers that cause bowel obstruction include colon, stomach and ovarian cancer. Other types of cancer (e.g., lung cancer) can spread to the abdomen and cause obstruction. Sometimes bowel function may be altered in cancer without actual spread of the cancer to the intestines (paraneoplastic syndrome).