Transabdominal Ultrasound Measured Rectal Diameter for Identifying Fecal Impaction in Children With Functional Constipation: A Diagnostic Accuracy Study.

Background Functional constipation (FC) is a common pediatric disorder, with fecal impaction posing significant diagnostic challenges. Digital rectal examination (DRE), to identify fecal mass in the rectum, is invasive and often distressing. Transabdominal ultrasound (TAUS) offers a promising, non-invasive alternative by measuring transverse rectal diameter (RD). This study was conducted to evaluate the diagnostic accuracy of ultrasound-measured RD in detecting fecal impaction among children with FC, using DRE as the reference standard. Methods In this diagnostic accuracy study conducted over 18 months, 80 children aged six months to 18 years with FC were recruited and divided into impaction (n=40) and non-impaction (n=40) groups. All cases underwent clinical evaluation, DRE, and blinded TAUS assessment. Mean RD was compared between the two groups, and subgroup analysis was performed to compare mean RD across age groups and fecal impaction status. Receiver operating characteristic (ROC) analysis was used to determine optimal RD cutoffs for diagnosing fecal impaction across two age groups (<4 years and >4 years). Results The mean transverse rectal diameter was significantly larger in the impaction group (mean = 3.38 cm, SD = 1.32) compared to the non-impaction group (mean = 2.15 cm, SD = 0.93), indicating a large effect size (Cohen's d = 1.07, p < 0.001). The subgroup >4 years with fecal impaction had significantly larger RD (mean = 3.62, SD = 1.49) compared to the same age group without fecal impaction (mean = 2.1, SD = 1.16, p < 0.001). ROC analysis showed moderate accuracy for an RD cut-off of 2.5 cm in children <4 years (sensitivity 60%, specificity 68.75%, AUC = 0.616) and higher accuracy at a 3.5 cm cut-off for children >4 years (sensitivity 63.3%, specificity 95.8%, AUC = 0.803). Rectal wall thickness did not significantly differ between the groups. Conclusion Ultrasound-measured RD is a valuable, non-invasive diagnostic tool for identifying fecal impaction in pediatric functional constipation, particularly in children over four years, when using age-specific cut-off values. Larger multicentric studies are required to confirm and refine the cut-off values. Incorporating transabdominal ultrasound into routine practice may enhance patient comfort while maintaining diagnostic accuracy.