Synchronous colorectal carcinomas.

Eighteen (5.0%) out of 358 patients who underwent resection of a colorectal carcinoma during the period 1978 through 1990 had synchronous colorectal carcinomas, and were 5.6 years younger on average than those with a single carcinoma. The distance between synchronous lesions was less than 10 cm in 69.6% of all the patients in the study. Among the synchronous carcinomas there was a higher incidence of ascending colon involvement, mucinous carcinoma, family history of malignant diseases, multiple malignant neoplasms associated with other organs and benign neoplastic polyps of the colorectum, and it is suggested that hereditary oncogenic factors influence these carcinomas. The synchronous lesions were detected pre-operatively in 14 of 18 patients with synchronous carcinomas, and the most common reason why synchronous lesions were missed was that the lesions on the anal side prevented the lesions on the proximal side from being examined. The prognosis in the synchronous lesion group was worse than in the solitary lesion group. Since it is difficult to predict synchronous colorectal carcinomas, careful pre-operative examination, including that of other organs, is necessary, and intra-operative colonoscopy should be carried out when pre-operative examination was insufficient.