A polyp is a growth of tissue from the intestinal or rectal wall that protrudes into the intestine or rectum and may be noncancerous (benign) or cancerous (malignant). Polyps vary considerably in size, and the bigger the polyp, the greater the risk that it is cancerous or precancerous. Polyps may grow with or without a stalk. Those without a stalk are more likely to be cancerous than those with a stalk. Adenomatous polyps, which consist primarily of glandular cells that line the inside of the large intestine, are likely to become cancerous (that is, they are precancerous). Serrated adenomas are a particularly aggressive form of adenoma.
Some polyps are the result of hereditary conditions, such as familial adenomatous polyposis and Peutz-Jeghers syndrome.
In familial adenomatous polyposis, 100 or more precancerous polyps develop throughout the large intestine and rectum during childhood or adolescence. In nearly all untreated people, the polyps develop into cancer of the large intestine or rectum (colorectal cancer) before age 40. People with familial adenomatous polyposis can develop other complications (previously termed Gardner's syndrome), particularly various types of noncancerous tumors. These noncancerous tumors develop elsewhere in the body (for example, on the skin, skull, or jaw).
In Peutz-Jeghers syndrome, people have many small polyps in the stomach, small intestine, large intestine, and rectum. They also have numerous bluish black spots on their face, inside their mouth, and on their hands and feet. The spots tend to fade by puberty except for those inside the mouth. People with Peutz-Jeghers syndrome have an increased risk of developing cancer in many organs, particularly the pancreas, small intestine, colon, breast, lung, ovary, and uterus.
Symptoms and Diagnosis
Most polyps do not cause symptoms. When they do, the most common symptom is bleeding from the rectum. A large polyp may cause cramps, abdominal pain, or obstruction. Large polyps with tiny, fingerlike projections (villous adenomas) may excrete water and salts, causing profuse watery diarrhea that may result in low levels of potassium in the blood (hypokalemia). Rarely, a rectal polyp on a long stalk drops down and dangles through the anus.
A doctor may be able to feel polyps by inserting a gloved finger into the rectum, but usually polyps are discovered during flexible sigmoidoscopy (examination of the lower portion of the large intestine with a viewing tube). If flexible sigmoidoscopy reveals a polyp, colonoscopy is performed to examine the entire large intestine. This more complete and reliable examination is performed because more than one polyp is usually present and any may be cancerous. Colonoscopy also allows a doctor to perform a biopsy (removal of a tissue sample for examination under a microscope) of any area that appears cancerous.
Doctors generally recommend removing all polyps from the large intestine and rectum because of their potential to become cancerous. Polyps are removed during a colonoscopy procedure using a cutting instrument or an electrified wire loop. If a polyp has no stalk or cannot be removed during colonoscopy, abdominal surgery may be needed.
If a polyp is found to be cancerous, treatment depends on whether the cancer is likely to have spread. The risk of spread is determined by microscopic examination of the polyp. If the risk is low, no further treatment is necessary. If the risk is high, particularly if the cancer has invaded the polyp's stalk, the affected segment of the large intestine is removed surgically, and the cut ends of the intestine are rejoined.
When a person has a polyp removed, the entire large intestine and rectum are examined by colonoscopy a year later and then at intervals determined by the doctor. If such an examination is impossible because of a narrowing of the large intestine, a barium enema may be used to view the large intestine on x-ray.
For people with familial adenomatous polyposis, complete removal of the large intestine and rectum eliminates the risk of cancer. Alternatively, the large intestine is removed and the rectum is joined to the small intestine. This procedure sometimes eliminates the rectal polyps and thus is preferred by many experts. The remaining part of the rectum is inspected by sigmoidoscopy every 3 to 6 months, so that new polyps can be removed. If new polyps appear too rapidly, however, the rectum must also be removed. If the rectum is removed, a surgical opening is created through the abdominal wall from the small intestine (ileostomy). Bodily wastes are eliminated through the ileostomy into a disposable bag.
Some nonsteroidal anti-inflammatory drugs (NSAIDs) are being studied for their ability to reverse the growth of polyps in people with familial adenomatous polyposis. Their effects are temporary, however, and once these drugs are discontinued, the polyps begin to grow again.
Last full review/revision December 2007 by Elliot M. Livstone, MD