Magnetic resonance imaging following the demonstration of a normal common bile duct on ultrasound in children with suspected choledocholithiasis: what is the benefit?

Background: The role of MRI in evaluating children with an in situ gallbladder and suspected choledocholithiasis following a negative or inconclusive US is unclear. Objective: To determine whether MRI benefits children with suspected choledocholithiasis and a normal common bile duct (CBD) without stones on US. Materials and methods: We conducted a retrospective 10-year review of paired US and MRI (within 10 days) in children 18 years or younger with suspected choledocholithiasis. With MRI as a reference standard, two reviewers independently evaluated the images for CBD diameter, choledocholithiasis, cholelithiasis and pancreatic edema. Serum lipase was recorded. We calculated exact binomial confidence limits for test positive predictive values (PPVs) and negative predictive values (NPVs) using R library epiR. Results: Of 87 patients (46 female, 41 male; mean age 14 years, standard deviation [SD] 4.6 years; mean interval between US and MRI 1.6 days, SD 1.8 days), 55% (48/87) had true-negative US, without CBD dilation/stones confirmed on MRI; 5% (4/87) had false-positive US showing CBD dilatation without stones, not confirmed on MRI; 33% (29/87) had true-positive US, with MRI confirming CBD dilatation; and 7% (6/87) had false-negative US, where MRI revealed CBD stones without dilatation (2 patients) and CBD dilatation with or without stones (4 patients). Patients with false-negative US had persistent or worsening symptoms, pancreatitis or SCD. The overall US false-negative rate was 17% (6/35). Normal-caliber CBD on US without stones had an NPV of 89% (48/54, 95% confidence interval: 0.77–0.96). Conclusion: MRI adds little information in children with a sonographically normal CBD except in the setting of pancreatitis or worsening clinical symptoms. Further evaluation is warranted in children with elevated risk of stone disease.