Crohn disease is an inflammatory bowel disease. A surgical procedure is required in about 80% of cases. Surgery doesn't cure from Crohn's disease but the type of surgery remains important as there are several intraoperative risk factors for recurrence. Among these factors the microscopic inflammation at the resection margins. This is a crucial point, if the resection is too large there is a risk of short bowel syndrome, if the resection is too short (microscopic inflammation at resection site), there is a higher risk of postoperative recurrence (75% vs 46% at 18 months). Surgeons have to do a limited resection (2cm from macroscopic crohn disease). However this macroscopic non inflammatory resection margin can be microscopically inflammatory (up to 80%). Thus it is useful to evaluate if there is a microscopic inflammation at the resection margin. Moreover there is an increase interest for the role of the mesentery for recurrence but its role remains unclear. It is of interest to clarify the border between the inflammatory and non-inflammatory mesentery. Cellvizio is a confocal laser endomicroscopy providing the possibility of obtaining in vivo high-magnification images of the gut epithelium. This allows real-time examination of the gastrointestinal mucosa at the cellular and subcellular level. Cellvizio has never been used during surgery for Crohn disease. The aim of this study is to evaluate the intraoperative use of Cellvizio (using the CelioFlex microsonde) with an intravenous injection of fluorescein to determine the best ileal resection margins in Crohn disease.