Metachronous Colorectal Adenomas Occur Close to the Index Lesion

Goals:The aim of this study is to assess the spatial relationship between index and metachronous colorectal adenoma location.Background:After the complete excision of a human sporadic colorectal adenoma, patients are at elevated risk of developing a further metachronous adenoma. Data regarding the occurrence site of a metachronous colorectal adenoma relative to the index adenoma are scarce.Study:Prospectively maintained databases were interrogated to identify all colonoscopies and adenoma excisions performed over a 10-year period at a single university teaching hospital. Data for the colonic segments at which adenoma removal were reported at index and all subsequent colonoscopies were extracted and 2 allied data sets merged.Results:A total of 15,121 colonoscopies and 4759 polyp events were recorded. Four hundred fifty-two patients [296 male, 156 female, median (range) age 75 (32 to 100) y] developed at least 1 metachronous adenoma at follow-up colonoscopy. When single index events only are considered (ie, synchronous adenoma cases excluded), over 61% of metachronous adenomas were recorded in the same or an adjacent colonic segment. When the full span of the colon is considered, metachronous adenomas were more likely to occur in a section of the colon proximal to that of the index adenoma (41%& PLUSMN;5%) than the same (39%& PLUSMN;5%) or distal segment (20%& PLUSMN;5%; P=0.006; 1-way & chi;2 test).Conclusions:A metachronous human sporadic colorectal adenoma is more likely to be found in the same colonic segment to that of the index adenoma or 1 immediately adjacent. These data suggest a shared origin of metachronous adenoma with preceding lesions, supporting the existence of precancerous fields.