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Colorectal Polyps

James M. Church, MD
Head, Section of Endoscopy
Department of Colorectal Surgery
Cleveland Clinic, Cleveland, Ohio

"Polyp" is a descriptive term referring to a discrete elevation above the surface of an epithelium. Polyps arising from the gut epithelium are histologically heterogeneous, including the harmless hyperplastic (metaplastic in the English tradition), inflammatory, and lymphatic varieties. Solitary hamartomatous polyps (juvenile and Peutz-Jehger's polyps) are rare, usually unsuspected before removal and have little clinical significance. The most important polyp type is the neoplastic polyp, or adenoma.

Morson was the first to lay out the concept of the adenoma-carcinoma sequence, stating that most, if not all, colorectal adenocarcinomas arise in a pre-existing benign adenoma. There is extensive clinical and genetic evidence to support this concept. Adenomatous colorectal polyps are very common however: 20 to 25% of patients over 60 years of age have at least one. Colorectal cancer is also common but much less common than adenomas. Not every adenoma becomes malignant therefore. Estimates are that 1 in 100-200 will ultimately become an invasive cancer. There are some data to indicate which adenomas are more likely to be associated with colorectal cancer. These "high risk" adenomas include:

  • any adenoma containing severe dysplasia
  • adenomas >1cm diameter
  • adenomas containing >25% villous component
  • more than 3 synchronous adenomas of any size or type

Japanese studies consider "flat" adenomas to also be high risk, with a high rate of severe dysplasia and cancer. Controversy exists about the incidence and significance of flat adenomas in western countries.

A different category of a "high risk" adenoma is the one that is found in the colon of a patient with chronic ulcerative colitis. If the surrounding mucosa is normal, this may be treated as a sporadic adenoma. If the mucosa is affected by colitis, treat the adenoma as colitis-associated dysplasia. Thus, although all colorectal polyps are removed when seen, only patients with these "high-risk" adenomas deserve close endoscopic follow-up.

Polypectomy

Most adenomas are small (<1cm) and are easily removed by cold biopsy, hot biopsy or snare excision. Adenomas up to 3cm are also fairly easy to remove unless they are inaccessible. Large polyps can be difficult and have a high chance of containing some invasive malignancy. Depending on the comfort level of the endoscopist, colectomy may be indicated.

Polypectomy is associated with complications. The risk of immediate bleeding is highest when pedunculated polyps with thick stalks are snared. Pre-injection of the stalk with adrenalin may be wise. Delayed bleeding is more common after hot biopsy or snare of sessile polyps.

Perforation of the colon is relatively uncommon but is a particular concern during removal of right-sided colonic polyps where the bowel wall is thin. Attempted removal of a polypoid cancer or a lipoma is especially dangerous.

Rates of perforation after polypectomy range from 0.1% to 0.3% and rates of hemorrhage from 0.7% to 3.3%. These represent averages however, with complications more likely after removal of large, right sided, sessile polyps.

The "miss rate" of polyps is higher than we think. Rex et al have shown that 29% of small adenomas (<5mm), 13% of mid sized adenomas (6-9mm) and 6% of larger adenomas (>10mm) are missed. If these are the results of a carefully conducted, prospective study, miss rates in routine clinical practice are likely to be higher. The consequences of missing small polyps are unlikely to be dire, as shown by the National Polyp Study and by Hofstad et al. However that should not be a reason for complacency.

Polyps may be missed because of an incomplete exam, blind spots, poor preparation, too hasty and careless a scope withdrawal or just bad luck. The chances of missing a polyp are higher in poorly prepared bowel, and in patients with multiple polyps. The next colonoscopy should be sooner in these patients.

Malignant Polyps

Adenomatous polyps containing cancer present a dilemma for the endoscopist. Should the patient undergo colectomy or not? Many studies have addressed this point and recent recommendations are fairly uniform. Polyps with "unfavorable" histology are an indication for bowel resection while those with "favorable histology" can be spared.

Unfavorable histology

i. Cancer within 2mm of cut edge of stalk
ii. Poorly differentiated cancer
(iii. Lymphovascular invasion)

Unfavorable shape

Sessile tumor resected piecemeal

Sometimes patients with a malignant polyp are referred late and there can be difficulty finding the site of the polyp. Do not assume that the described location is accurate. Find the scar or remove half a colon. The diagnosis of invasive cancer is a polyps is not always reliable. Variation between pathologists may cause carcinoma in situ (severe dysplasia) to be reported as invasive cancer or vice versa. Misplacement of benign epithelium can also cause confusion. Review of pathology is an important part of treatment planning.

References

  1. Hofstad B, Vatn MH, Andersen et al. Growth of colorectal polyps: redetection and evaluation of unresected polyps for a period of three years. Gut 1996:39:449-456.
  2. Atkin WS, Morson BC, Cuzick J. Long term risk of colorectal cancer after excision of rectosigmoid adenomas. N Engl J Med 326: 658-662, 1992.
  3. Muto T, Kamiya J, Sawada T et al. Small "flat" adenoma of the large bowel with special reference to its clinicopathologic features. Dis Colon Rectum 1985; 28: 847-51.
  4. Rex DK, Cutler CS, Lemmel GT et al. Colonoscopic miss rates of adenomas determined by back to back colonoscopies. Gastroenterology 1997;112:24-28.
  5. Rex DK. Colonoscopic withdrawal technique is associated with adenoma miss rates. Gastrointest Endosc 51: 33-6, 2000.
  6. Hixson LJ, Fennerty MN, Sampliner RE et al. Prospective, blinded trial of the colonoscopic miss-rate of large colorectal polyps. Gastroinest Endosc 1991;37: 125-127.
  7. Volk E, Goldblum JR, Petras RE et al. Management and outcome of patients with invasive carcinoma arising in colorectal polyps. Gastroenterology 1995;109:1801-1807.
  8. Church JM. Endoscopy of the Colon, Rectum and Anus. 1995; Igaku Shoin, New York, Tokyo.