Extrahepatic bile duct measurement by using transabdominal ultrasound in Japanese adults: multi-center prospective study

Background In adults, less than 10-mm bile duct has idiomatically been recognized as “non-dilated bile duct” though there was no obvious evidence. The aim of this study was to prospectively examine the maximum inner diameter of extrahepatic bile duct (MDEBD) in consecutive adults. Methods Transabdominal ultrasound (US) was performed to measure the MDEBD of 8840 cases (4420 male) in five institutions. The frequency of ultrasound probe ranged from 3.5 to 5 MHz. Results The mean diameter of MDEBD was 4.5 ± 1.4 mm (range 1–14 mm). The relationship between the MDEBD and age was shown as follows: MDEBD = 2.83 + 0.03 × age. Multiple regression analysis was analyzed between 6 groups and significant α level is 0.008 in this analysis. In all age groups but 20s and 30s, there was statistically significant MDEBD among each age group ( p < 0.0001). Mean, mode value and median MDEBD is increasing according to the age as follows: 20s: 3.9 ± 1.0 mm, 30s: 3.9 ± 1.2 mm, 40s: 4.3 ± 1.2 mm, 50s: 4.6 ± 1.3 mm, 60s: 4.9 ± 1.4 mm, >70s: 5.3 ± 1.6 mm. Conclusion The present study revealed that MDEBD positively correlates with age. Therefore, when we examine the presence of dilation of the bile duct, our calculating formula appears to be suitable for accurate evaluation.