From the Guidelines
Common bile duct dilation is concerning when it exceeds 7-8 mm in diameter in adults with an intact gallbladder, or greater than 10 mm in patients who have undergone cholecystectomy, as indicated by the most recent and highest quality study 1.
Key Considerations
- The normal diameter of the common bile duct (CBD) can vary depending on age and other factors, but a diameter of less than 8 mm is generally considered normal in adults with an intact gallbladder 1.
- In patients who have undergone cholecystectomy, the upper limit of normal for CBD diameter may be slightly higher, typically up to 10 mm 1.
- Elderly patients may have a slightly higher upper limit of normal due to age-related ductal changes, with some studies suggesting up to 8.5 mm as a normal threshold 1.
- In children, the normal diameter of the CBD is smaller, and concern for dilation may arise at measurements above 4-6 mm depending on age 1.
Clinical Context
- The clinical context is crucial in interpreting CBD dilation, as asymptomatic mild dilation may be monitored in some cases, while even borderline dilation accompanied by symptoms like jaundice, abdominal pain, or abnormal liver function tests requires prompt investigation 1.
- Pregnant women may have physiologic dilation up to 8 mm due to hormonal effects, which typically resolves postpartum 1.
Further Evaluation
- When CBD dilation is detected, further evaluation with additional imaging (such as MRCP, ERCP, or endoscopic ultrasound) is typically warranted to determine the underlying cause 1.
- The choice of imaging modality may depend on the clinical context and the suspected underlying cause of the dilation, with MRCP or EUS often recommended for intermediate to high likelihood of CBD stones 1.
From the Research
Common Bile Duct Dilation
- The common bile duct (CBD) diameter can vary in size, and dilation can be a concern in certain situations.
- A study from 2 found that a dilated common bile duct of more than 12 mm on endoscopic retrograde cholangiography can be a sign of biliary tract disease.
- Another study from 3 reported that post-cholecystectomy patients with a large common bile duct dilation (mean diameter, 18 mm) and delayed contrast drainage may have sphincter of Oddi dysfunction.
Threshold for Concern
- A study from 4 suggested that asymptomatic bile duct dilation of up to 10 mm can be considered a normal range in patients after cholecystectomy.
- However, a case report from 5 showed that the common bile duct diameter can fluctuate rapidly during an episode of biliary colic, with a diameter of 17 mm decreasing to 4 mm within 5 hours.
- A study from 6 found that bariatric surgery can result in CBD dilation, with changes more pronounced after Roux-en-Y gastric bypass (RYGB) compared to sleeve gastrectomy (SG).
Factors Influencing Dilation
- Cholecystectomy status can influence CBD dilation, with some studies suggesting that dilation can occur regardless of cholecystectomy status 4, 6.
- The type of bariatric surgery may also affect biliary pathophysiology, with RYGB resulting in greater CBD dilation compared to SG 6.
- Other factors, such as sphincter of Oddi dysfunction, can also contribute to CBD dilation 3.