Differential Diagnosis of Cystic Bile Duct Dilations and Idiopathic Choledochectasia in Children: the Value of Ultrasound with a Functional Test

Objective . To evaluate the diagnostic efficacy of dynamic ultrasound with a choleretic load for differentiating between cystic bile duct dilations and idiopathic choledochectasia in children, based on analysis of data from patients with verified cysts and long-term prospective follow-up. Materials and Methods . A comprehensive study was conducted, including a retrospective analysis of 30 verified cases of cystic bile duct dilations (according to Todani classification: type I — 21, type II — 2, type IV — 6, type V — 1) and prospective follow-up of 67 children with idiopathic choledochectasia (common bile duct diameter >95th percentile for age) from 2016 to 2025. All children underwent comprehensive ultrasound; dynamic ultrasound was performed in 25 of them: measurement of the internal diameter of the common bile duct on an empty stomach and after oral administration of Hofitol (0.3 ml/kg, maximum 2.5 ml for children under 5 years and 5 ml for those over 5 years) at 15 minute intervals for one hour. A reduction in diameter of < 10 % from baseline was considered the criterion for absence of significant dynamics (suspicion of organic pathology). Results were compared with intraoperative findings and follow-up data (median follow up 24 months). Results . Among the 30 children with cystic bile duct dilations, girls predominated (n = 19, 63.3 %). Distribution according to Todani: type I — 21 (70 %), type II — 2 (6.7 %), type IV — 6 (20 %), type V (Caroli disease) — 1 (3.3 %). According to the Davenport classification, the cystic variant (1c, 4c) was observed in 11 patients (36.7 %), the fusiform variant (1f, 4f) in 16 (53.3 %); rare types (2, 5) accounted for 3 cases (10 %). Dynamic ultrasound with a choleretic load clearly separated the groups: in 5 patients with fusiform cysts (type 1f), the reduction was 1–7% (below the 10% threshold); in the choledochectasia group (n = 20), the mean reduction was 32.6 ± 11.4 % (p < 0.001). ROC analysis (n = 25) yielded an AUC of 0.987 (95 % CI 0.949–1.000; p < 0.001). With a 10 % cutoff, sensitivity in this subgroup was 100 %, specificity 95 %. Extrapolated to the entire cohort (30 cysts, 67 choledochectasia) using the 10 % threshold, sensitivity reached 100 % (all 30 patients with cysts had a reduction <10 %), specificity was 98.5 % (66 of 67 choledochectasia patients correctly identified), positive predictive value 96.8 %, and negative predictive value 100 %. In the prospective follow-up group (n = 67), spontaneous normalization of the common bile duct diameter occurred in 67.2 % of children with initially isolated asymptomatic choledochectasia; progression with development of clinical cyst manifestation was observed in only 1 case (1.5 %). Conclusion . Ultrasound with a functional test is a highly informative method for differentiating between cystic bile duct dilations and functional dilatation (AUC 0.987). The proposed algorithm avoids unnecessary surgical interventions in children with idiopathic choledochectasia and allows timely referral for surgical treatment of patients with true cysts.