Transverse Rectal Diameter: Predictor of Severity in Children With Chronic Functional Constipation

Background This study aims to evaluate transverse rectal diameter (TRD) as a predictor of clinical severity and response to conventional treatment in children with chronic functional constipation (CFC). Methods This longitudinal prospective study enrolled 105 children aged 4–17 years with CFC at Fondazione Policlinico A. Gemelli (Rome, Italy) from December 2021 to April 2025. We used the Constipation Scoring System (CSS), pelvic ultrasound (TRD, anterior wall thickness [WT], detrusor thickness [DT]), and follow‐up assessments at 2, 4, and 6 months. Patients without TRD or CSS improvement at 6 months underwent high‐resolution anorectal manometry (HR‐ARM). Statistical analysis included generalized linear mixed‐effects models. Results Children with megarectum (TRD ≥ 3 cm) showed higher CSS scores ( p = 0.002), TRD ( p = 0.001), WT ( p = 0.021), and longer constipation duration ( p = 0.005) compared to controls. TRD positively correlated with age ( p = 0.008) and CSS ( β = 1.41, p = 0.043). A significant reduction in TRD and WT was observed at 2 months posttreatment ( p < 0.001). Nine patients who failed to improve had type I dyssynergia confirmed on HR‐ARM. DT showed no significant correlation with clinical severity. Conclusion TRD measured by pelvic ultrasound is a reliable noninvasive marker for assessing severity and monitoring treatment response in pediatric CFC. Persistence of rectal dilatation may suggest underlying defecatory dyssynergia and guide further evaluation. Integration of TRD into routine practice could improve personalized, outpatient‐based care. Further multicentric studies are needed to validate TRD as a predictive biomarker in long‐term management.