Effect of preoperative colonoscopy on the incidence of synchronous and metachronous neoplasms.

Colonoscopy and air-contrast barium enema performed preoperatively in 389 patients with colorectal cancer revealed synchronous cancer in 4% and polyp in 14%. Nine of the 16 synchronous cancers were located in other surgical segments than the index cancer, and six of the nine were in stage A or B1. Of the 54 synchronous polyps, 28 were located in such other segments. Half of the synchronous cancers and almost half of the synchronous polyps were missed at double-contrast barium enema. All synchronous cancers and three-fourths of the synchronous polyps were detected at colonoscopy. No patient with preoperative colonoscopy presented with metachronous cancer within 3 years from surgery, and only two were subsequently found to have adenocarcinoma arising from an adenomatous polyp. Endoscopic polypectomy was performed in 21 cases during follow-up. Extensive use of preoperative colonoscopy is recommended in the evaluation of colorectal cancer, in order to promote detection of synchronous tumors, reduce the incidence of 'early metachronous' cancer and avoid malignant degeneration of adenomatous polyp.