From the Guidelines
The normal size of the common bile duct typically ranges from 3 to 6 millimeters in diameter in adults. This measurement is taken from the inner wall to inner wall of the duct. The common bile duct may dilate slightly with age, and in individuals over 60 years old, a diameter of up to 8 millimeters can still be considered within normal limits 1. After cholecystectomy (gallbladder removal), the common bile duct may also appear slightly larger, with measurements up to 10 millimeters sometimes accepted as normal.
Key Points to Consider
- The size of the common bile duct is important clinically because dilation beyond these parameters may indicate obstruction, such as from gallstones, tumors, or strictures.
- Measurement is typically performed using ultrasound, CT scan, MRCP (magnetic resonance cholangiopancreatography), or ERCP (endoscopic retrograde cholangiopancreatography) 1.
- The common bile duct gradually increases in diameter from its origin at the junction of the hepatic ducts to its termination at the ampulla of Vater, where it enters the duodenum.
Diagnostic Considerations
- Ultrasound is recommended by many organizations, including the American College of Gastroenterology, as the initial diagnostic test of choice in patients with suspected obstruction of the common duct 1.
- The presence of multiple small (<5 mm) gallstones in the gallbladder creates a 4-fold risk for migration of these stones into the CBD 1.
- A normal CBD caliber on US has a 95% to 96% negative predictive value 1.
From the Research
Normal Size of Common Bile Duct
The normal size of the common bile duct (CBD) can vary depending on age and other factors.
- The mean width of the CBD for all age groups in normal cases was 3.4 mm (range 2 to 11 mm) 2.
- Another study found that the mean diameter of the CBD was 4.1 mm (SD 1.01 mm), with an average diameter ranging from 2.0 mm to 7.9 mm 3.
- A more recent study reported a mean diameter of the common bile duct of 4.04 ± 1.11 mm, with a minimum of 1.9 mm and a maximum of 8.8 mm 4.
- The diameter of the CBD tends to increase with age, with one study finding a mean diameter of 3.8 ± 0.87 mm for patients under 30 years, and 6.9 ± 0.8 mm for patients over 70 years 4.
- The normal size of the CBD can also be influenced by other factors, such as the presence of cholelithiasis or pancreatic disease, which can cause the CBD to become wider 2.
Factors Affecting CBD Size
Several factors can affect the size of the CBD, including:
- Age: The diameter of the CBD tends to increase with age 2, 3, 4.
- Presence of cholelithiasis: The mean width of the CBD was 4.5 mm (range 2 to 15 mm) in patients with cholelithiasis 2.
- Presence of pancreatic disease: The CBD was wider in patients with pancreatic disease, with a mean width of 6.2 mm (range 2 to 21 mm) 2.
- Sex: One study found no statistically significant difference in CBD diameter between male and female subjects 3.
- Anthropometric measurements: One study found no statistically significant correlation between CBD diameter and anthropometric measurements such as height, weight, and chest circumference 3.