SUMMARY In a prospective necropsy study of the large bowel in 365 cases, the commonest polyp identified was the hyperplastic (metaplastic) variety, of which 86. 1% of the total were located in the rectum. The other main type of polyp found, and of much greater importance because of its malignant potential, was the neoplastic adenoma. These were present, either singly or multiply, in 73 of 198 male cases (36.9%) and in 48 of 167 female cases (28.7%). Their prevalence and their tendency to be multiple rose with increasing age in both sexes. Most adenomas had a tubular growth pattern and 88.8% of these were under 1 cm in diameter. There was a fairly even distribution of adenomas throughout the large bowel but a higher proportion of adenomas over 1 cm in diameter occurred in the caecum, sigmoid colon, and rectum than at other sites. In the whole series nine adenocarcinomas were present, two of which were arising in adenomas.There is much clinical, experimental, and pathological evidence that the vast majority of carcinomas of the large bowel arise from adenomas, a process referred to as the adenoma-carcinoma sequence.1 The only obvious exception to this is in the case of cancer arising in long-standing ulcerative colitis, where the precursor dysplastic lesion is not a discrete polyp, but often affects a wide area of the bowel, which macroscopically may be flat or have a poorly circumscribed velvety or nodular appearance.Whereas there is a mass of information relating to the incidence and distribution of colorectal carcinomas, much less is known about adenomas.The aim of our prospective study was to determine the prevalence and distribution of adenomas in a consecutive study of cases at necropsy. Over a period of approximately one year, the large bowel was examined in all cases coming to necropsy within 48 hours of death. This amounted to 365 specimens, 134 of which came from cases dying in hospital. The remaining 231 specimens were from necropsies ordered by a coroner where death had occurred outside hospital. An additional eight specimens were excluded, three where an antemortem diagnosis of large bowel cancer had been made, three where extensive autolysis precluded histological diagnosis, and two cases where the anorectal junction was not included in the specimen.
MethodsAt necropsy, with the large bowel in situ, plastic clips were placed at the hepatic and splenic flexures and at the proximal and distal ends of the sigmoid colon (the point where the colon passes the inlet of the true pelvis, and the upper border of the S3 segment of the os sacrum, respectively). A portion of the terminal ileum and the whole of the large bowel, including the anorectal junction, was then removed and opened along the antimesenteric border. After washing out the contents, the total length of the bowel and its subdivisions were measured. The size, site, and configuration of any mucosal polyp was recorded on a proforma. The bowel was then pinned out flat on a cork board and immersed in a tank of 10% buffered formalin for at least 24 ho...
