Background and study aims: Patients who have had a colorectal adenoma are likely to develop a metachronous adenoma, and therefore need to be kept under surveillance. The question is whether metachronous adenomas will be found at the same anatomical site as the preceding adenomas, thus prompting us to focus surveillance examinations on this region, using flexible sigmoidoscopy or total colonoscopy.
Patients and methods: Between 1978 and 1996 a long-term follow up of 1091 patients was prospectively documented at the Erlangen Registry of Colorectal Polyps. The anatomical sites--distal (rectosigmoid) and proximal colon--of two subsequent generations of metachronous adenomas were analysed using logistic regression analysis.
Results: In 556 (51%) patients metachronous adenomas were found during follow up. In 211 (37.9%) of these patients a right-sided shift in the first generation of metachronous adenomas in comparison with initial lesions (P<0.0001) was found. Some 305 patients underwent further follow up, and 51 (27.1%) out of 188 patients with metachronous lesions demonstrated a right-sided shift in their second generation (vs. first generation) of metachronous adenomas. Proximally located first generation metachronous adenomas would be missed by flexible sigmoidoscopy in 50.8% of patients with only distal adenomas at baseline colonoscopy, and in 58.7% of patients with second-generation lesions. Multivariate analysis revealed that multiplicity (odds ratio 2.64, 95% CI 1.49-4.66) and size of initial adenomas (>5 mm) (odds ratio 3.60, 95% CI 1.96-6.66) were significantly associated with a right-sided shift in metachronous adenomas, while female gender was associated with a significantly lower tendency to manifest a right-sided shift (odds ratio of 0.64. 95% CI 0.43-0.94).
Conclusions: Metachronous adenomas are found significantly more often in the right colon than would be expected assuming clustering at the same anatomical site as the preceding lesions. Total colonoscopy is thus needed for surveillance, regardless of the initial adenoma site.