Objective Severe endoscopic lesions (SEL) in patients with colonic Crohn's disease (CD) have been linked to higher risk of colectomy. The aims of this study were to reassess the predictive value of colonoscopy compared against MRI for requirement of resection surgery in patients with CD and determine the influence of current therapeutic options.

Design In this single-centre, observational, prospective, longitudinal study, patients with an established diagnosis of CD and suspected activity were included. After baseline assessment, including colonoscopy and MRI, patients were followed until resection surgery or the end of study.

Results 112 patients were eligible for analysis. Ulcers were present in 94/112 (84%) of patients at colonoscopy (SELs in 51/112 (46%)) and stenosis in 38/112 (34%). MRI identified ulcers in 79/112 (71%) of patients, stenosis in 36/112 (32%) and intra-abdominal fistulae in 20/112 (18%). Surgical resection requirements (29/112 (26%)) were not associated with the presence of SELs at colonoscopy. The presence of stenosis (p<0.001) or intra-abdominal fistulae (p<0.001) at MRI correlated with a higher risk of surgery. In the multivariate analysis, perianal disease (OR 9 (2 to 39), p=0.003), stenosis (OR 3.4 (1 to 11), p=0.04) and fistulae at MRI (OR 10.6 (2 to 46), p=0.002) increased the risk of abdominal resection surgery, while months under immunomodulators (OR 0.94 (0.90 to 0.98), p=0.002) and/or antitumor necrosis factor (anti-TNF) therapy (OR 0.97 (0.94 to 1), p=0.04) during follow-up decreased this risk.

Conclusions Perianal disease, stenosis and/or intra-abdominal fistulae at MRI independently predict an increased risk of resection surgery in patients with CD, whereas immunosuppressants and/or anti-TNF therapy reduce such risk. Under current therapeutic strategies, the presence of SELs is not a predictor of resection surgery in patients with CD.