Correlation between axial and coronal common bile duct diameters in computed tomography: a retrospective study of 1064 patients

Background: The measurement of the common bile duct (CBD) diameter is essential for evaluating bile duct pathologies. The axial plane of computed tomography (CT) images is the established method for CBD diameter measurement. However, modern software enables easy reconstruction of axial CT images into the coronal plane, allowing for CBD diameter measurement in this plane. This study aimed to investigate the correlation between measurements in the axial and coronal planes. Results: The three reviewers demonstrated fair reliability in measuring CBD diameter in axial and coronal planes, with intraclass correlation coefficients of 0.776 and 0.799, respectively. A positive correlation was observed between the two diameters (r = 0.943), with 88.9% of axial diameter variation explained by coronal diameter and approximately 0.29 + (0.94 × coronal diameter) (R² = 0.889, p < 0.001). When a cutoff value of 7 mm was used to predict an abnormal axial diameter, the agreement between axial and coronal CBD diameters was substantial (Kappa = 0.715) with discordance between the two measurements identified in 6.2% of cases (66/1064) when a) coronal diameter < 7 mm but axial measurement ≥ 7 mm (39/1064; 3.7%) and b) coronal diameter ≥ 7 mm but axial measurement < 7 mm (27/1064; 2.5%). In univariable linear regression and multivariable analyses, the strongest independent factors associated with increased axial CBD diameter were presence of focal CBD lesion, age ≥ 60 years, and cholecystectomy. Conclusion: There was a strong positive correlation between axial and coronal CBD diameters with substantial agreement when using a 7-mm cutoff and fair reliability in their measurements.