Intestinal ultrasound for monitoring postoperative Crohn's disease: A systematic review and clinical implications.

BACKGROUND: Postoperative recurrence is common in Crohn's disease (CD), with endoscopic lesions in a majority of patients by 12 months after surgery. Ileocolonoscopy is the reference standard but is invasive and poorly suited to frequent surveillance. Intestinal ultrasound (IUS) - including small intestine contrast ultrasound and contrast enhanced ultrasound - is a repeatable, noninvasive alternative. AIM: To summarize the evidence on the diagnostic accuracy and prognostic value of IUS for detecting postoperative recurrence in CD. METHODS: We systematically searched PubMed and EMBASE through June 2025 for original English-language studies evaluating IUS against clinical or endoscopic outcomes in postoperative CD. This scoping review was conducted and reported in accordance with the Preferred Reporting Items for Systematic reviews and Meta-Analyses guideline. After screening 259 unique records, 41 full texts were assessed and 20 studies were included. RESULTS: Bowel wall thickness thresholds of ≥ 5 mm at the neo-terminal ileum predict endoscopic recurrence with sensitivities 81%-94% and specificities 86%-100%; lower cutoffs at the anastomosis (≥ 3-3.5 mm) also carry risk (data from singlecenter cohorts). Dualsite assessment (neo-terminal ileum + ileocolonic anastomosis) improves performance. Adding Doppler hyperemia or mesenteric lymphadenopathy increases accuracy; combining bowel wall thickness ≥ 3 mm with fecal calprotectin ≥ 50 μg/g yields high specificity (approximately 93%-100%) with a negative predictive value of nearly 95% when both are negative. Contrast enhanced ultrasound-based composite scores reach approximately 98% diagnostic accuracy in prospective cohorts. Small intestine contrast ultrasound shows similarly strong early diagnostic performance - for example, an area under the receiver operating characteristic curve up to 0.95 when using ileocolonic anastomosis wall thickness ≥ 3 mm to 3.5 mm plus lesion length, with 82%-94% sensitivity and > 90% specificity reported even within 7 days post-resection. Overall, IUS shows moderate agreement with endoscopy (κ approximately 0.5-0.8) and stronger prognostic value when performed within 12 months post-surgery. CONCLUSION: IUS can be integrated into postoperative surveillance algorithms - particularly within the first year - and can reduce routine endoscopy in selected patients. Research priorities include standardized thresholds and composite scoring, consensus training/competency, and multicenter validation including artificial intelligenceassisted interpretation.