Objective: Intestinal ultrasound (IUS) is a noninvasive tool for detecting and monitoring disease activity in children with inflammatory bowel disease (IBD). Remission values for bowel wall thickness (BWT) are extrapolated from adult data. We aimed to define normal BWT in children with IBD in sustained deep remission.

Methods: Multicenter, retrospective pediatric IUS database including children with IBD, without a history of surgery or complications, who underwent IUS after achieving sustained deep remission, defined as the absence of ulcerations on ileocolonoscopy and/or transmural healing on magnetic resonance enterography and steroid-free clinical remission for ≥6 months. Univariate and multivariable analyses were performed using mixed-effect modeling.

Results: Ninety-eight children (40 [41%] female; 64 [5%] Crohn's disease [CD]: 29 (30%) ulcerative colitis [UC]: 5 (5%) IBD-unspecified), median age 15.2 [13.8-16.8] years), and 484 bowel segments were included. Median BWT was 1.4 (1.1-1.6) mm, with no difference in BWT between bowel segments (p = 0.28). In multivariable analysis, a positive association remained between BWT and weight (univariate β = 0.004 [95% confidence interval, CI = 0.001-0.007], p = 0.016, multivariate β = 0.006 [95% CI = 0.001-0.011], p = 0.041). A negative association remained between BWT and disease duration (unadjusted β = -0.024 [95% CI = -0.047 to -0.001] p = 0.046, adjusted β = -0.028 [95% CI = -0.052 to -0.003], p = 0.039).

Conclusions: Previously inflamed BWT for children with IBD in sustained deep remission was less than 2.5 mm, which is less than 3 mm in adults, and unaffected by age, sex, and bowel segment in this population. BWT may be affected by weight and disease duration. These findings are crucial to the standardized assessment of transmural healing in children.