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. 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.
A single measurement of the bile duct can be misleading as the duct may be normal at this point, yet be distended lower down in early obstructive jaundice. Thus, the common bile duct was measured at three locations- at the porta hepatis, in the most distal aspect of head of pancreas and mid-way between these points [ Table/Fig-1 ]. Ultrasonographic measurement of CBD at three locations. All the physical measurements were conducted in a separate area, screened off to provide privacy. The following procedures were adopted for conducting anthropometric measurements : Subjects were asked to stand with their feet together with weight evenly distributed over both feet and with their arms relaxed at the sides during the measurements. 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. We studied a total of 200 subjects; wherein an equal proportion belonged to either sex. The study subjects belonged to the age group 18-85 years of age; the mean age was 34.5 years (SD 13.24 years). A majority of the participants belonged to the age group 18-25 years. The mean age for males was 35.8 years while that for females was 33.1 years. This difference in ages was not statistically significant. The mean weight and height of the participants was 51.4 kg (SD 12.25 kg) and 163.4 cm (SD 9.98 cm) respectively. The mean circumference measured at levels of chest, transpyloric plane, umbilicus and hip were 83.5 cm (SD 9.04 cm), 75.2 cm (SD 9.94 cm), 78.1 cm (SD 12.02 cm) and 87.2 cm (SD 10.0 cm) respectively. [Table/Fig-2]: Mean and standard deviation of common bile duct diameter by age group. Age Group (in completed years) Number of Participants Mean (mm) Standard Deviation (mm) 18-25 70 3.9 0.86 26-35 50 4.0 0.91 36-45 46 4.1 1.17 46-55 23 4.4 1.23 >55 11 4.7 0.81 Total 200 4.1 1.01. In order to compare the diameter across the five age groups, and test the null hypothesis that the groups have the same common bile duct diameters, we applied the Analysis of Variance (ANOVA). The difference was found to be statistically significant (p = 0.05). Further, we applied a test for linear trend on the age-wise distribution of common bile duct diameter. This was found to be statistically significant (p = 0.003), with an F-statistic of 8.78. 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). In order to assess the association between common bile duct diameter and anthropometric measurements, both of which were continuous variables, correlation was used. Common bile duct diameter was not observed to have statistically significant correlation with any of the anthropometric measurements.
The diameter was not observed to have statistically significant correlation with any of the anthropometric measurements among either sex [ Table/Fig-3 ]. [Table/Fig-3]: Summary of correlation between common bile duct diameter and anthropometric measurements by sex. Anthropometric Measurement Male Female Correlation Coefficient Sig. (p-value) Weight - 0.01 0.851 0.13 0.177 Height - 0.02 0.782 0.01 0.863 Chest circumference 0.03 0.712 0.09 0.328 Circumference at transpyloric plane 0.04 0.684 0.18 0.071 Circumference at umbilicus 0.08 0.421 0.09 0.340 Circumference at hip - 0.03 0.771 0.07 0.432. This study was conducted among 200 normal subjects belonging to the state of Rajasthan. An equal number of males and females in the age group 18-85 years of age were included in the study. The subjects underwent ultrasonographic measurements of common bile duct diameters by experienced radiologist at the Mahatma Gandhi Medical College and Hospital at Jaipur, India. In addition, anthropometric data on weight, height, chest circumference, circumference at transpyloric plane, circumference at umbilicus and circumference at hip were obtained for each of the study subjects.
The mean diameter observed in our study was 4.1 mm with a standard deviation of 1.01 mm. This was similar to that reported by Parulekar  in his study on 200 normal subjects.