2-10 IMPORTANCE OF ADENOMAS 5 MM OR LESS IN DIAMETER THAT ARE DETECTED BY SIGMOIDOSCOPY
Increased use of flexible sigmoidoscopy has increased detection of benign adenomatous polyps < 5 mm in diameter (referred to as diminutive) in the rectosigmoid of asymptomatic patients.
Should patients with diminutive adenomas undergo complete colonoscopy?
This prospective study determined the prevalence of proximal colonic neoplasms in asymptomatic patients at average risk for colorectal cancer (CRC) who were found to have diminutive benign adenomas on screening flexible sigmoidoscopy.
Conclusion: Colonoscopy is warranted.

STUDY

1. Prospectively performed colonoscopy in 200 patients (mean age 62) who had an adenoma in the rectosigmoid discovered by screening flexible sigmoidoscopy.
2. Adenomas classified as: (1) diminutive = 5mm; (2) small 6 to 10mm; and (3) large > 10 mm.
3. Patients with a positive fecal occult blood test were excluded.

RESULTS

1. Neoplasms were found in the proximal colon in: 1) 29% of those with diminutive index adenomas; 2) 29% of those with small index adenomas, and 3) in 57% of those with large adenomas.
2. Colonoscopy discovered advanced neoplasms (adenomas > 10 mm in diameter, adenomas with a villous component or moderate-to-severe dysplasia, carcinoma in situ, or frank carcinoma in 6% of those with diminutive adenomas; in 10% of those with small adenomas; and in 29% of those with large adenomas (Two patients with diminutive index adenomas had proximal carcinoma in situ; two had proximal stage I carcinomas. One patient with a large index adenoma had proximal stage III carcinoma.)
3. The presence of multiple diminutive rectosigmoid adenomas was not predictive of advanced proximal neoplasms.
4. Increased size of the proximal adenoma correlated with the prevalence of advanced proximal neoplasms.

DISCUSSION

1. "We found that asymptomatic, average risk patients with diminutive or small rectosigmoid adenomas on screening flexible sigmoidoscopy have a 29 percent prevalence of proximal neoplasms at colonoscopy."
2. Patients with diminutive or small rectosigmoid adenomas also have a substantial prevalence of advanced proximal neoplasms (6%-10%).
3. Neoplastic change in the distal colon may be a marker for neoplastic change in the proximal colon.
4. Carcinoma can exist in small adenomas. In one study 1 of malignant polyps were less than 10mm in diameter. Removal of even diminutive colorectal adenomas may prevent the development of colorectal carcinoma.
5. Screening colonoscopy has been advocated by some because of its ability to detect proximal neoplasms in the absence of distal neoplasms. Cost would be great.

CONCLUSION
The substantial prevalence of proximal colonic neoplasms, including advanced lesions, in asymptomatic average-risk patients with rectosigmoid adenomas warrants colonoscopy.

NEJM January 2, 1997; 336: 8-12 Original investigation from Lahey-Hitchcock Medical Center, Burlington, Massachusetts

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