From the Guidelines
A normal bile duct diameter should be less than 8 mm. When evaluating the common bile duct (CBD) diameter, it's essential to consider various factors, including age, as the diameter can increase by 1 mm per decade after age 60 1. The CBD diameter can be measured using different imaging modalities, such as trans-abdominal ultrasound, endoscopic ultrasound (EUS), magnetic resonance cholangiopancreatography (MRCP), and computed tomography.
- Trans-abdominal ultrasound is often used as a first-line imaging test due to its wide availability, but it has a low sensitivity in detecting CBD stones, ranging from 25 to 63% 1.
- MRCP has a high accuracy in detecting CBD stones, surpassing 90%, but may struggle with detecting small stones 1.
- EUS is a minimally invasive procedure that is superior to endoscopic retrograde cholangiography (ERC) in detecting malignant causes of cholestasis and is at least equal to ERC in terms of stone detection 1. Key points to consider when evaluating CBD diameter include:
- The widest point of the CBD is often measured in the distal portion near the pancreatic head.
- Recent meals and medications that affect sphincter of Oddi function can temporarily affect CBD diameter.
- A CBD diameter greater than 7-8 mm in younger adults or exceeding age-appropriate limits in older adults may suggest pathology such as obstruction from stones, strictures, or tumors 1.
From the Research
Normal CBD Diameter
- The normal diameter of the common bile duct (CBD) varies with age, with a mean width increasing from 2.8 mm in the age group 20 years or younger to 4.1 mm in patients 71 years of age or older 2.
- A study found that the mean diameter of the CBD in normal patients was 3.4 mm, with a range of 2 to 11 mm 2.
- Another study reported a mean diameter of 4.1 mm, with a range of 2.0 mm to 7.9 mm, and an upper limit of normality of 7.9 mm 3.
- The diameter of the CBD also increases with age, from 3.9 mm among those aged 18-25 years to 4.7 mm among those in the age group more than 55 years 3.
Diagnostic Methods
- Endoscopic ultrasound (EUS) and magnetic resonance cholangiopancreatography (MRCP) are tests used in the diagnosis of common bile duct stones, with high diagnostic accuracy 4.
- Ultrasound is also used as a screening test for the diagnosis of common bile duct stones, with a summary sensitivity of 0.73 and a specificity of 0.91 5.
- Liver function tests, such as serum bilirubin and serum alkaline phosphatase, can also be used to diagnose common bile duct stones, but their diagnostic accuracy varies depending on the cut-off values used 5.
CBD Dilation
- A CBD diameter of ≥ 7 mm in patients with intact anatomy or ≥ 10 mm in patients with prior cholecystectomy is considered dilated 6.
- EUS is a useful diagnostic method for patients with unexplained CBD dilation, especially in patients with older age, abdominal pain, jaundice, cholelithiasis, and/or altered liver biochemistry 6.
- CBD diameter in ultrasound and computed tomography can predict a positive EUS in asymptomatic patients without altered liver biochemistry 6.