The portion of the large intestine that extends from the cecum to the rectum is referred to as the colon. The chief function of the colon is to extract moisture from indigestible matter prior to its excretion. Similar to other parts of the body, the tissues of the colon may give rise to various types of abnormal growths. Many of these tumors are cancerous, but others are benign.

Often when they are benign and arise from a mucus membrane, they are referred to as polyps. Colonic polyps are extremely common and are estimated to occur in about half of all people greater than 60 years of age. As many as 75 percent of polyps found in the colon are classified as adenomas, tumors that originate in glandular tissue or exhibit a glandular structure.

Villous adenomas are usually sessile polyps that have an architecture predominantly characterized by the presence of finger- or frond-like projections. These growths are more likely than any other type of adenoma to become cancerous. According to current estimates, the risk of a villous adenoma undergoing malignant transformation is as high as 25 percent overall, and is even greater for growths larger than 2 centimeters in diameter.

Polyps in the rectum are occasionally palpable by rectal examination, but more often require examination via endoscopy to be discovered. Thus, individuals who are at an elevated risk of developing colonic polyps are generally advised to undergo regular screening in order that adenomas and other benign tumors may be detected before they grow to significant sizes, in which case they are associated with a higher rate of malignant change. Screening techniques that are commonly utilized include stool specimen tests for occult blood, which is blood that cannot be seen by the unaided eye, and flexible sigmoidoscopy, which involves the insertion of a tubular instrument into the anus in order that the lower portion of the colon can be visualized.

Some studies suggest that regional differences in colonic polyp rates are related to dietary differences, the growths most commonly being associated with high-fat diets low in fiber and excessive alcohol intake. Cigarette smoking has also been linked to an increased risk of developing adenomas. Such lifestyle-related risk factors are under personal control and can be modified to help reduce the possibility of growths forming in the colon. There also appears, however, to be a genetic factor involved in polyp development that cannot be changed.

Colon Villous Adenoma at 40x Magnification - Although adenomas are generally benign tumors, they are prone to malignant change and may become cancerous over time if not removed. They are, however, the least frequently appearing variety of adenomatous polyp, accounting for only about 5 percent of the growths.

Colon Villous Adenoma at 20x Magnification - Several subtypes of adenomas have been described. These subtypes are primarily differentiated from one another by microscopic observation of the manner in which the cells of the abnormal growths are organized.

Colon Villous Adenoma at 10x Magnification - The prevalence of adenomas increases with age and the growths are more common among individuals living in certain regions of the world, primarily highly developed nations such as the United States and Great Britain.

Colon Villous Adenoma at 40x Magnification - Though the exact causes of villous adenomas and other colonic polyps are not known, there are several known risk factors for the growths and steps that may be taken in order to reduce the likelihood of developing them.

Colon Villous Adenoma at 20x Magnification - Villous adenomas and other polyps rarely present symptoms except in very advanced cases. When they do occur, however, they may include abnormal bleeding, cramps, abdominal pain, constipation, or diarrhea.