From the Research
The normal size of the common bile duct (CBD) is typically less than 6 mm in diameter in adults, with an upper limit of normality of 7.9 mm, as reported in a study published in 2014 1. This measurement can vary slightly based on age, with a general rule allowing for an increase in diameter with age. The size of the CBD is clinically important because dilation beyond these parameters may indicate obstruction from gallstones, tumors, or other pathologies. Key points to consider when evaluating the size of the CBD include:
- The CBD tends to be slightly larger in elderly patients, with a diameter of up to 8-10 mm potentially being considered within normal limits.
- Measurements should be taken when the patient is fasting, as the duct can temporarily dilate after meals due to normal physiological response to food intake.
- The duct is measured using ultrasound, CT, or MRI imaging, with measurements taken at the widest portion, usually in its mid-portion. A study published in 2014 1 found that the mean diameter of the CBD was 4.1 mm, with an average range of 2.0 mm to 7.9 mm, and 95% of subjects having a diameter of less than 6 mm. Another study published in 1983 2 reported a mean width of the CBD of 3.4 mm, with a range of 2 to 11 mm, in normal patients. However, the most recent and highest quality study, published in 2014 1, provides the most accurate and reliable information on the normal size of the CBD.