This study aims to collect data by multidetector computed tomography (MDCT) on the diameter of the normal common bile duct (CBD) and the diameter of CBD after cholecystectomy. In this retrospective study, CBD measurements were performed on axial oblique images, perpendicular to the long axis of the distal CBD. The mean diameter of the normal CBD was measured in 604 patients without cholecystectomy. The patients were divided into 6 groups according to their age. Analysis of variance (ANOVA) was used to compare data obtained from the six age groups. The mean diameter of the CBD of 46 patients who had cholecystectomy was calculated. The results were compared with age matched control group by Student's t test. The largest diameter of CBD ranged from 1.8 to 11.8mm. The mean of the largest diameter of 604 subjects was 4.77 ± 1.81. The diameter of the CBD significantly increased with age. Mean largest CBD diameters of postcholecystectomy subjects (7.28 ± 2.37) were significantly greater than age matched control group. In conclusion the diameter of CBD shows a considerable increase with age. The largest diameter of the CBD is up to 6mm in most of the subjects. An upper limit of 8mm appears reasonable after the age of 50; and an upper limit of 10mm seems appropriate for cholescystectomized subjects.
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