Colorectal mass lesions masquerading as chronic inflammatory bowel disease on mucosal biopsy

AIMS: We bring to the attention of diagnostic pathologists a further cause of mimicry of chronic inflammatory bowel disease on mucosal biopsy, namely intramural and subserosal colorectal mass lesions. METHODS AND RESULTS: In a 10-year prospective study in one centre, we describe 26 cases in which the initial colonoscopic biopsies suggested a diagnosis of chronic inflammatory bowel disease, whereas subsequent information indicated that the mucosal changes were due to underlying mass lesions, without evidence of chronic inflammatory bowel disease. These mass lesions included underlying primary adenocarcinoma, metastatic carcinoma, pneumatosis, endometriosis and complicated diverticular disease. CONCLUSIONS: In the colon and rectum, intramural and subserosal mass lesions are a significant cause of chronic inflammatory bowel disease mimicry. Possible pathogenic mechanisms include mechanical effects, lymphatic obstruction by underlying tumour, relative mucosal ischaemia and mucosal prolapse. Since the changes seen on mucosal biopsies are a secondary phenomenon, we tentatively suggest that 'secondary colitis' may be an appropriate appellation.