Reference Value for The Diameter of The Common Bile Duct and Pancreatic Duct on MRCP: Based on Age and Gender

Magnetic Resonance Cholangiopancreatography (MRCP) is a non-invasive imaging technique that plays a crucial role in the evaluation of the biliary and pancreatic ductal systems. Introduced in the early 1990s, MRCP has revolutionized hepatobiliary diagnostics by enabling detailed visualization of the intrahepatic and extrahepatic biliary tree as well as the main pancreatic duct (MPD), without the need for contrast agents or invasive procedures like Endoscopic Retrograde Cholangiopancreatography (ERCP) [1,2]. MRCP utilizes heavily T2-weighted MRI sequences to generate high-contrast images of stationary fluids, such as bile and pancreatic secretions, making the ducts appear hyperintense against a suppressed background [3]. Unlike other imaging modalities, such as ultrasonography or computed tomography, MRCP is less influenced by bowel gas, body habitus, or operator dependency, and does not expose patients to ionizing radiation [4]. One of the primary clinical applications of MRCP is the detection of obstructive pathologies such as choledocholithiasis, biliary strictures, and pancreatic neoplasms. In such cases, accurate measurement of ductal diameters is essential for diagnosis and management [5]. However, the diameters of the common bile duct (CBD) and MPD can vary significantly depending on multiple factors including age, gender, cholecystectomy status, and ethnic background [6,7]. For example, physiological dilation of the CBD is common in older adults and in individuals who have undergone cholecystectomy, sometimes mimicking pathological conditions [8,9]. Despite the availability of global reference values, there remains a lack of region-specific normative data for MRCP-based measurements, particularly in rural and semi-urban Indian populations. Most existing standards are derived from Western or urban Asian cohorts, and may not be appropriate for diverse populations such as those in Western Uttar Pradesh [10,11]. Misinterpretation of physiological variations as pathological can lead to unnecessary interventions, increased patient anxiety, and avoidable healthcare costs [12]. Given these concerns, this study aims to establish age- and gender-specific reference values for CBD and MPD diameters in asymptomatic adults using MRCP in Western Uttar Pradesh. By providing locally relevant data, this research intends to enhance diagnostic accuracy and support evidence-based interpretation of hepatobiliary imaging.

METHOD

2.1 Study Design and Setting

This was a cross-sectional, observational study conducted at the Department of Radiodiagnosis, SCPM Hospital and Research Centre, Gonda, Uttar Pradesh, India. The study aimed to determine normative reference values for the common bile duct (CBD) and main pancreatic duct (MPD) diameters using Magnetic Resonance Cholangiopancreatography (MRCP) in asymptomatic individuals across different age groups and genders.

2.2 Study Population

2.2.1 Inclusion Criteria

• Adults aged between 20 and 70 years
• Asymptomatic individuals undergoing MRCP for routine or non-specific abdominal complaints
• Normal liver function tests (LFTs)
• No known hepatobiliary or pancreatic disease

2.2.2 Exclusion Criteria

• History of hepatobiliary or pancreatic disease (e.g., chronic pancreatitis, gallstones)
• Previous biliary or pancreatic surgeries (excluding post-cholecystectomy subgroup analysis)
• Abnormal LFTs or imaging suggesting pathology
• Pregnant individuals or those with contraindications to MRI (e.g., pacemakers, metallic implants)

2.3 Sample Size and Sampling Technique

A total of 100 participants were included in the study. The sample size was calculated based on the standard deviation (SD) of CBD diameter reported in previous literature (1.5 mm), a 95% confidence interval (Z = 1.96), and a permissible error (d) of 0.3 mm. The formula used for sample size estimation was:

n=(Z⋅σd)2

After adjusting for potential dropouts, 100 was considered an adequate sample size. A purposive sampling technique was used to ensure proportional representation of all age categories and both genders.

2.4 Data Collection Procedure

1. Eligible participants were recruited following referral for MRCP imaging.
2. Informed consent was obtained after screening for inclusion and exclusion criteria.
3. Participants underwent MRCP on a 1.5 Tesla MRI scanner (Philips/Siemens).
4. A standardized MRCP protocol was followed, including:
   • Fasting for 4–6 hours prior to imaging
   • Heavily T2-weighted single-shot fast spin-echo (SSFSE) sequences
   • Respiratory gating and breath-hold technique
   • 3D acquisition for maximum intensity projection (MIP) and multiplanar reconstruction (MPR)
5. Duct diameter measurements were performed using the inbuilt DICOM viewer.
   • CBD was measured at its widest extrahepatic portion.
   • MPD was measured at the head region for consistency, as it typically shows the largest diameter.
   • All measurements were taken in millimeters (mm).
6. To ensure inter-observer reliability, measurements were independently performed by two radiologists. Any discrepancies exceeding 0.5 mm were resolved by consensus.
7. Intra-observer reliability was tested by re-measuring 20 randomly selected cases after a 1-week interval, with a Kappa coefficient >0.85 confirming consistency.

2.5 Study Variables

Dependent Variables:

• Diameter of the Common Bile Duct (CBD)
• Diameter of the Main Pancreatic Duct (MPD)

Independent Variables:

• Age (in years)
• Gender (male/female)
• Cholecystectomy status (yes/no)

2.6 Data Analysis

Data were compiled in Microsoft Excel and analyzed using SPSS v25.0. Statistical methods included:

• Descriptive Statistics: Mean, standard deviation (SD), minimum and maximum values
• Inferential Statistics:
  • T-tests to assess the effect of gender and cholecystectomy on duct diameters
  • One-way ANOVA to evaluate age-group differences
  • Pearson’s correlation coefficient (r) to assess relationships between age and duct diameters
• Significance Threshold: p < 0.05 was considered statistically significant

2.7 Ethical Considerations

The study protocol was approved by the Institutional Ethics Committee (IEC) of SCPM College of Nursing & Paramedical Sciences. Written informed consent was obtained from all participants before inclusion. Patient confidentiality and data privacy were strictly maintained.

2.8 Quality Control Measures

• Standardized MRCP imaging protocols
• Dual-observer measurements to reduce bias
• Periodic calibration of imaging equipment
• Strict inclusion/exclusion screening to maintain sample homogeneity

RESULTS

This section presents the analysis of MRCP-based measurements of the common bile duct (CBD) and main pancreatic duct (MPD) diameters across various age groups, genders, and cholecystectomy status in 100 asymptomatic individuals.

3.1 Demographic Profile

A total of 100 participants were included in the study. The sample was stratified into three age groups: 20–39 years (38%), 40–59 years (40%), and 60–70 years (22%). Gender distribution was relatively balanced, with 53% male and 47% female participants. Among them, 16% had a history of cholecystectomy.

The majority of participants were in the 20–59-year range, with fewer individuals above 60 years. Cholecystectomy cases were most frequently observed in older participants, aligning with clinical trends of gallbladder disease prevalence increasing with age.

3.2 Duct Diameters by Age Group

Table 3.1: Mean and Range of CBD and MPD Diameters by Age Group

Interpretation:
There is a clear, statistically significant trend of increasing CBD and MPD diameters with advancing age. The mean CBD diameter increased from 5.70 mm in the 20–39 group to 7.40 mm in the 60–70 group. Similarly, MPD diameter increased modestly from 2.11 mm to 2.44 mm. These findings confirm age as a major determinant of physiological ductal dilation.

3.3 Duct Diameters by Cholecystectomy Status and Gender

Table 3.2: CBD and MPD Diameters by Cholecystectomy Status and Gender