Background: Computed tomography (CT) is widely used in diagnosis of biliary disorders in adults yet there is no data on the normal common bile duct (CBD) size of the average Thai adult. This study attempts to establish a reference normal measurement for CBD diameter for the Thai population.
Results: Mean diameter of CBD ranged from 2.3 to 9.5 mm. The mean of the mean diameter of 277 subjects was 4.65±1.39 mm. The diameter of the CBD significantly increased with age (p<0.05), and are not significantly related to gender.
Material and method: 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 277 patients. The patients were divided into 7 groups according to their age. Analysis of variance (ANOVA) was used to compare data obtained from the seven age groups.
The mean diameters of the common bile duct in the three locations were: proximal, 4.0 mm (SD 1.02 mm); middle, 4.1 mm (SD 1.01 mm); and distal, 4.2 mm (SD 1.01 mm). The overall mean for all measures was 4.1 mm, with a standard deviation of 1.01 mm. All the three diameters were highly correlated and statistically significant (p-value<0.001). While the lower limit of common bile duct diameter among the normal subjects was 2.0 mm, the upper limit was found to be 7.9 mm. However, 95% of the study participants showed a common bile duct diameter of < 6 mm.
[ Table/Fig-2 ] shows the distribution of common bile duct diameter by age group. The diameter was found to increase progressively from 3.9 mm among those aged 18-25 years of age to 4.7 mm among those in the age group more than 55 years of age.
Height was measured using a stadiometer with a sensitivity of 0.1 centimeter. The weighing scale with a sensitivity of 0.1 kg was used to measure weight. Chest circumference was measured using a measuring tape over light clothing and while breathing normally. In the males, the measurement was made at the widest point of the chest; in the females, the measurement was made at the level of the nipples with the measuring tape held horizontally. The circumference at the transpyloric plane was measured at a level midway between the suprasternal notch (at the upper border of manubrium between the sternal heads of sternomastoid muscles) and the symphysis pubis (at the lower end of median line). Circumference at the umbilicus was obtained by measuring the abdominal circumference using measuring tape at the level of the umbilicus. Circumference at the hip was measured with the measuring tape positioned around the maximum circumference of the buttocks.
Materials and Methods
Ultrasonography is an accurate, safe, non-invasive and inexpensive imaging modality, which is highly sensitive and specific for the detection of many biliary tree diseases . Ultrasonography is comparable in accuracy to oral cholecystography, radionuclide studies, computed tomography and magnetic resonance imaging, and more cost-effective .
Socio-demographic details related to age, sex and place of residence were recorded for each subject. The ultrasonographic findings with regard to common bile duct diameter were obtained. In order to reduce observer bias, the same expert radiologist was involved in conducting ultrasonography for all subjects. A 3.5 megahertz (MHz) transducer was used. The common bile duct was identified through its association with the portal vein in the long axis of the gallbladder. At this location the common bile duct and hepatic artery appear as two smaller circles anterior to the portal vein, giving an appearance of a face with two ears – also called a ‘Mickey Mouse’ sign. With the indicator directed toward the patient’s right, the right ear is the common bile duct and the left ear, the hepatic artery.
We did not find any statistically significant correlation of common bile duct diameter with sex. This finding was similar to other studies by Niederau et al., , Admassie , Reinus et al., , Adibi and Givechian , Brogna et al.,  and El Sharkawy E et al., .
The mean diameter of common bile duct was observed to be 4.1 mm (SD 0.95 mm) for males and 4.0 mm (SD 1.07 mm) for females. This difference was tested by applying independent samples t -test. The t value was 0.86, which was not found to be statistically significant (p = 0.38).
The GB EF as a percentage was calculated as follows:
There are some limitations to the current study. First, dogs weighing over 15 kg were excluded from the study. Therefore, further study of larger dogs is needed. Moreover, the accuracy, sensitivity, and specificity of the normal status cut-off value were not evaluated due to the small sample size of the cholestatic group.
This is an Open Access article distributed under the terms of the Creative Commons Attribution Non-Commercial License (http://creativecommons.org/licenses/by- nc/4.0) which permits unrestricted non-commercial use, distribution, and reproduction in any medium, provided the original work is properly cited.
The obtained CT images displaying an abdominal window (window level = 40 HU, window width = 400 HU) were analyzed by using the same software as used in experiment 1. All CT measurements performed in experiment 1 were performed identically in experiment 2.
US evaluation of the common bile duct (CBD) in dogs has been used to evaluate biliary system obstruction, and the diameter of a normal CBD was previously proposed to be 3 mm [ 23 ]. A limitation of US assessments for GB and CBD is its dependence on operator skill and the difficulty in evaluating various GB shapes [ 12 ]. In addition, CBD scanning using US is thought to lack reproducibility due to reverberation artifacts secondary to the presence of intestinal gas and changes in CBD diameter during respiration [ 11 ]. In human medicine, several diagnostic methods including US, computed tomography (CT), magnetic resonance cholangiopancreatography, endoscopic US, and endoscopic retrograde cholangiopancreatography have been used to evaluate CBD diameter and determine the cause of dilation [ 2 , 3 , 6 , 15 , 16 , 19 , 21 ]. Among these modalities, CT examination allows detailed visualization of the biliary tract, assessment of the cause of any dilation, and differentiation of malignant and benign lesions. In human medicine, visibility of normal CBD and the hepatic duct in CT imaging has been reported in 82% and 66%, respectively, of normal subjects [ 15 , 21 ].