Polyps are outgrowths of tissue from the mucosal surface of a cavity. These growths are not unique to the small and large intestine and may be see anywhere in the gastrointestinal tract like esophageal and stomach polyps and also occurs within other cavities like nasal polyps in the nose and uterine polyps in the uterus.
Intestinal polyps are protrusions from the mucosal surface of the intestine into the lumen. Most polyps are seen in the colon. Polyps are overgrowths of tissue and may extend along the mucosal surface (sessile) or protrude outwards into the lumen with a stalk (pedunculated). An intestinal polyp may be single or multiple and can vary in size from a few millimeters to several centimeters.
Malignant or Benign Intestinal Polyps
Intestinal polyps are benign growths that can be categorized as neoplastic or non-neoplastic. Neoplastic growths occur when individual normal cells replicate independently due to genetic abnormalities and have the potential to become malignant (cancerous). Non-neoplastic polyps do not have the potential to become malignant. Neoplastic polyps of the intestine include adenomatous polyps (adenomas of the colon) and are the more common type of polyp of the intestine. Non-neoplastic polyps include inflammatory, hyperplastic, lymphoid and juvenile intestinal polyps.
Adenomatous polyps (colorectal adenomas) are fairly common and may occur in up to 50% of people over the age of 60 years. Only 10 to 20% of these polyps will become malignant. Adenomas can be classified by its shape – villous, tubular or tubulovillous. As the name suggest, villous adenomas are growths with multiple projections due to folding of the surface, similar to the villi seen in the small intestine. Villous adenomas secrete large quantities of mucus similar to the surrounding intestinal epithelium. These types of polyps have been discussed in greater detail under adenomatous polyps.
Non-adenomatous types of intestinal polyps can develop as a result of inflammation, abnormal maturation of mucosa or abnormal architecture. The non-adenomatous polyps are not as dangerous as the adenomatous polyps since most do not have the potential to become malignant (non-neoplastic). The non-adenomatous polyps can be hyperplastic, lymphoid, inflammatory, or juvenile in type.
Hyperplastic (Metaplastic) Polyps
Most of the patients with non-adenomatous polyps have hyperplastic type of polyps. Hyperplastic polyps usually result from the abnormal maturation of the mucosal cells of the intestines and are usually of small size. Hyperplastic polyps are mostly found in sigmoid colon or rectum and occur in association with hyperplastic polyposis syndrome in some patients.
Lymphoid polyps are seen in association with hyperplasia (enhanced cell division) of lymphoid tissue in the intestinal mucosa. It is often benign and is seen in parts of the intestine where lymphoid tissues are concentrated like the ileum of the small intestine or rectum. Lymphoid polyps are formed of well differentiated lymphoid tissue.
Inflammatory polyps are seen in patients suffering from inflammatory diseases of the intestine like ulcerative colitis or Crohn’s disease. The inflammatory polyps have areas of inflammation and ulceration. Unlike other non-adenomatous polyps, inflammatory polyps are associated with an increased risk of cancer.
Also known as congenital or retention polyps, these type of polyps develop in the rectum of children below 5 years of age. It is usually a result of localized abnormal development of the normal tissue. Juvenile polyps are usually found incidentally but sometimes can be found in relation to rectal bleeding or intestinal obstruction. Asymptomatic juvenile polyps do not require any therapy. Juvenile polyps can also be seen as a part of some hereditary syndromes like Peutz Jegher’s syndrome or juvenile polyposis syndrome. The latter has an increased risk of colon cancer.
Signs and Symptoms of Intestinal Polyps
Most intestinal polyps are asymptomatic, meaning that it does not cause any symptoms. It may only be discovered upon examination for other gastrointestinal symptoms during endoscopic investigation – upper GI or colonoscopy. An intestinal polyp is more likely to cause symptoms as it increases in size. However, in some cases, even small polyps may be symptomatic. Some of the signs and symptoms include :
- rectal bleeding
- blood in stool
- change in bowel habits (diarrhea or constipation)
- abdominal pain
Less commonly, large polyps may lead to intestinal obstruction. Read more on blocked bowel (small intestine) or blocked colon (large intestine). Large polyps with long pedicles may prolapse through the anus. Villous adenomas tend to secrete copious quantities of mucus and when coupled with diarrhea, hypokalemia (abnormally low levels of potassium in the blood) may arise.