Prevalence and clinical significance of proximal colorectal adenomas in asymptomatic, average-risk subjects

Abstract

Background. Current recommendations for colorectal cancer screening in people at average risk (asymptomatic, age > 50, no other risk factors) are yearly fecal occult blood test (FOBT) and flexible sigmoidoscopy every five years starting at age 50. However, FOBT often fail to detect polyps, and flexible sigmoidoscopy, although effective in reducing colorectal cancer mortality, only examines the distal portion of the colon. The use of colonoscopy for colorectal cancer screening in average-risk subjects is still controversial. Aim. To determine the prevalence and the clinical significance of proximal colonic polyps in a group of asymptomatic, average risk patients according to presence or absence of rectosigmoid adenomas (sentinel lesions), commonly believed to be markers of neoplastic changes throughout the colon warranting colonoscopy. Methods. Among 961 consecutive subjects referred to our center, we identified all those with a successful total colonoscopy. Two hundred and seventy-one subjects had at least one adenomatous polyp: of these, 79 were excluded from this analysis because of reported signs or symptoms (positive FOBT, change in bowel habit, hematochezia), prior history of colon polyps or cancer, prior colon evaluation, or positive family history. The remaining 192 patients constituted the study group. All polyps were removed and pathological evaluation was obtained. Adenoma number, size and location were determined at colonoscopy. Advanced adenomas were defined as tubulo-villous, villous or large (> 10 mm in diameter). Results. Among the 192 asymptomatic, average risk patients (males 63%; mean age-+ SD: 58.8 ± 7.2) 136 (70.8%) had adenomas in the sigmoid rectum, while 56 patients (29.2 %) had only proximal polyps in the absence of sentinel lesions in the sigmoid rectum. Among patients with adenomas in the sigmoid rectum, the prevalence of additional proximal adenomas was 17.6 % (24/136). Sentinel lesions were distinguished on the basis of their size as follows: diminutive, 10 ram. We found that 1 of the 4 patients with diminutive index polyps had proximal advanced adenomas, as did 7/12 patients with small index lesions and 7/8 patients with large index lesions. The prevalence of advanced adenomas among the 56 patients who harbored only proximal polyps was 50% (28/56); ten of these patients had multiple polyps. Conclusions. In our study, asymptomatic subjects at average risk of developing coloreetal cancer showed a high prevalence of proximal adenomas in the absence of sentinel lesions in the sigmoid rectum. Half of these lesions were of a type considered at high risk for the development of further adenomatous polyps or cancer. Since these patients would be missed with the current screening strategies, we believe that these findings support the use of colonoscopy for colorectal cancer screening.