Introduction
Background
Colonic polyps are slow-growing overgrowths of the colonic mucosa that carry a small risk (<1%) of becoming malignant. However, because colonic polyps are highly prevalent in the general population (especially with increasing age), they confer an important predisposition to colon cancer and are therefore removed when detected.
Patients with isolated colonic polyps are usually asymptomatic but can experience overt or occult colonic bleeding. Colonic polyps can occur as part of inherited polyposis syndromes in which their number is greater and the risk for malignant progression is much greater compared to the risk with isolated colonic polyps.
In the context of clinical studies of chemoprevention, efforts are being directed at suppressing colonic polyp formation (eg, by use of sulindac) and/or at preventing their progression to colon cancer (eg, by use of aspirin).
Pathophysiology
Colonic polyps, or adenomas, are benign epithelial neoplasms that arise from the epithelial cells lining the colon. Colonic polyps are traditionally divided into 3 groups, as follows: hyperplastic polyps, adenomas, and polyposis syndromes.
Hyperplastic polyps
Hyperplastic polyps comprise about 90% of all polyps and are benign protrusions. They are usually less than 0.5 cm in diameter. Hyperplastic polyps most commonly occur in the rectosigmoid region during adulthood.
Thought previously to be entirely clinically insignificant, hyperplastic polyps are now recognized to possess some malignant potential in the setting of hyperplastic polyposis syndrome. Patients who are affected have an occurrence of hyperplastic polyps proximal to the sigmoid colon, with (1) 2 or more that are greater than 10 mm in diameter, (2) a total of more than 30 polyps, or (3) a first-degree relative with the syndrome. The polyps in this syndrome may have adenomatous components; display a serrated, saw-tooth surface epithelium; and harbor methylation of specific target genes, including mismatch repair genes.
Adenomas
Adenomas comprise approximately 10% of polyps. Most polyps (approximately 90%) are small, usually less than 1 cm in diameter, and have a small potential for malignancy. The remaining 10% of adenomas are larger than 1 cm and approach a 10% chance of containing invasive cancer.
Adenomas are traditionally divided by histology into 3 types, as follows: tubular, tubulovillous, and villous. Tubular adenomas are the most common of the 3 types and can be found anywhere in the colon. Villous adenomas most commonly occur in the rectal area; tend to be larger than the other two types; and tend to be nonpedunculated, velvety, or cauliflowerlike in appearance. Villous adenomas are associated with the highest morbidity and mortality rates of all polyps. They can cause hypersecretory syndromes characterized by hypokalemia and profuse mucous discharge and can harbor carcinoma in situ or invasive carcinoma more frequently than other adenomas.
Thus, the risk of progression to carcinoma is related to both the size and the histology of the adenoma. Adenomas that are greater than 1 cm, contain a substantial (>25%) villous component, or have high-grade dysplasia are commonly referred to as advanced neoplasms and carry an increased cancer risk.
The shape or gross structure of the polyp is also clinically significant. Those polyps with a stalk are called pedunculated. Those polyps without a stalk are called sessile. Sessile polyps are more concerning than large pedunculated polyps for two reasons. First, the pathway for migration of invasive cells from the tumor into submucosal and more distant structures is shorter. Second, the complete endoscopic removal is more challenging and more difficult to ascertain.
Some premalignant neoplasia is now recognized to be flat, rather than protuberant. Such nonpolypoid neoplasia is more common in the setting of chronic colitis and may be detected more readily by nontraditional endoscopic imaging methods, such as narrow-band width imaging or mucosal staining
Frequency
United States
Population and autopsy studies suggest that about 30% of middle-aged or elderly individuals have colonic polyps. In comparison, the incidence of FAP in the United States is 1 case for every 6580-8300 persons.
International
Accurate comparison of colonic polyp incidence and prevalence among countries is difficult because of differences in the methods used for detection. Colonic polyp prevalence in patients older than 60 years appears to vary substantially within and among countries, but it appears to be greater than 10% in most areas.
Mortality/Morbidity
Untreated, colonic polyps can and do progress to carcinoma over several years. Morbidity from colonic polyps is related to complications, such as bleeding, diarrhea, intestinal obstruction, and progression to cancer. Bleeding can be frank hematochezia but is often chronic and goes unnoticed by the patient. If uncompensated, intestinal blood loss can cause anemia, typically due to iron deficiency.
A study by Stryker et al suggests that the risk of cancer development from sporadic 1-cm colonic polyps is 8% at 10 years and 24% at 20 years.1 The risk for cancer development depends on the size of the polyp, villous histology, and its association with polyposis syndromes. In FAP, cancer inevitably develops 10-20 years after the initial appearance of colonic polyps.
Race
Race per se is not a major risk factor for colonic polyps. However, studies indicate that blacks have a somewhat higher incidence and an earlier onset of colorectal carcinoma. An American Gastroenterological Association task force recommended beginning colorectal cancer screening in blacks at age 45 years, rather than the standard age of 50 years.
Sex
Males may have a modestly higher colonic polyp incidence than females.
Age
Colonic polyps are strongly associated with increasing age (typically after age 40 y), but they can occur early in patients with polyposis syndromes. For example, colonic polyps can be detected in adolescents with familial adenomatous polyposis or in patients aged 20-40 years with hereditary nonpolyposis colorectal cancer (HNPCC).
Clinical
History
- History of present illness
- Most patients with colonic polyps are asymptomatic.
- In symptomatic patients, the most common presenting symptom is rectal bleeding. Other symptoms include diarrhea or constipation, often with decreased stool caliber.
- Villous adenomas of the rectum and distal colon can occasionally manifest as a syndrome of severe diarrhea with massive fluid and electrolyte loss.
- Chronic bleeding from colonic polyps may cause iron deficiency anemia.
- Family history: Although colonic polyps are a disease of older individuals, a positive family history of polyposis should prompt referral for screening in younger individuals and, in some cases, at more frequent intervals. A common practice is to begin screening in a patient 5 years earlier than the age at which colonic polyps were diagnosed in a first-degree relative.
Physical
- Distal rectal polyps can be detected by digital rectal examination. Otherwise, physical examination findings are typically normal.
- Occult blood in stools (detected by guaiac and antibody-based tests) may be found in a minority of patients with colonic polyps.
- Although nonspecific, this finding should prompt a colon evaluation in most patients.
- Such evaluations have had similar yields of clinically significant findings whether the stool sample was obtained by digital rectal examination or was retrieved from spontaneously passed stools.
Causes
- Epidemiologic studies suggest that environmental causes contribute to differences in colonic polyp incidence in geographically distinct populations, but the responsible factors have remained elusive.
- Differences in consumption of dietary fiber and antioxidants have been hypothesized to play a role in the development of colonic polyps, but these proposals have not been substantiated in recent studies. There is limited, circumstantial evidence that consumption of meat, fat, and alcohol may be risk factors. Conversely, consumption of calcium and folate may confer a modest protective effect, particularly in patients with a history of colonic polyps and low basal consumption levels.
- Genetics
- A number of polyposis syndromes have been described. These can be associated with specific extraintestinal manifestations as well as extraintestinal tumors.
- Identification and characterization of the genetic factors leading to the various syndromes is progressing. Most of the mutant genes in these syndromes have been identified.
- At the genetic level, FAP is understood best. This is an autosomal dominant disorder caused by truncating mutations in the adenomatous polyposis coli (APC) gene.
- Hereditary nonpolyposis colorectal cancer (HNPCC) is an autosomal dominant disorder caused by mutations in DNA mismatch repair proteins.
- Cowden disease is associated with mutations in the phosphatase and tensin homology on chromosome 10 (PTEN) protein phophatase.
More on Colonic Polyps |
 Overview: Colonic Polyps |
| Differential Diagnoses & Workup: Colonic Polyps |
| Treatment & Medication: Colonic Polyps |
| Follow-up: Colonic Polyps |
| References |
| Next Page » |
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Further Reading
Keywords
colonic polyps, colonic polyp, colon polyp, colon polyps, colon cancer, colon cancer polyp, colon, colonoscopy, colonoscopy polyp, polyps in colon, polyps in the colon, adenomas, hyperplastic polyps, benign epithelial neoplasms, polyposis syndromes, familial adenomatous polyposis, FAP, Gardner syndrome, Turcot syndrome, Peutz-Jeghers syndrome, Cowden disease, familial juvenile polyposis, hereditary nonpolyposis colorectal cancer, HNPCC, dysplasia-associated lesion or mass, DALM, sulindac, polypectomy, colectomy
