Definition of age dependent reference values for diameter of the common bile duct and pancreatic duct on MRCP from a population based cohort study

Introduction:

Changes in diameters of the pancreaticobiliary ducts are markers of diseases including benign conditions like chronic pancreatitis, bile duct stones or pancreaticobiliary malignancies. MRCP (magnetic resonance cholangiopancreatography) is the first line, non-invasive imaging modality for duct configuration, with broad availability and ever increasing accuracy. However, the reference ranges in asymptomatic individuals and their change with age and after medical procedures have only been studied in small cohorts.

Aims and Methods:

To define new reference values for diameters of pancreaticobiliary ducts on MRCP in the general population and to identify factors influencing duct size. Study subjects were recruited from the general population based SHIP and had whole body MRI + MRCP (1,5T MRI system). Diameters of pancreatic duct (PD) and common bile duct (CBD) were measured on MRCP maximal intensity projection sequence before and after administration of secretin by an investigator blinded to other subject data.

Results:

1385 subjects were initially scanned, 865 measured PDs and 938 CBDs were included for further analysis. Subjects were excluded for missing data or evidence of pancreaticobiliary disease (post-cholecystectomy n = 115, cholecystolithiasis n = 57, choledocholithiasis n = 8, chronical pancreatitis n = 17, pseudocysts n = 52, cholestasis n = 11, liver cirrhosis n = 1, hepatitis n = 2). Median age was 53y (21 – 89y) and 48.5% were female. The diameters increased with age (PD median (range) 1.-3. Quartile: 20 – 29 years 1.33 cm (1.20 – 1.57), > 70 years 2.49 (1.85 – 3.01); CBD median (range) 1.-3. Quartile: 20 – 29 years 4.53 (3.87 – 5.17), > 70 years 6.50 (5.10 – 8.23)) and the historic upper limit of normal of 3 mm for PD and 7 mm for CBD were exceeded by 11% and 18.2% respectively. Subjects that underwent cholecystectomy presented with significantly increased diameter of CBD, but not PD (CBDw/oCCE: 5.30 mm ± 1.893 SD vs. CBDw/CCE: 8.18 mm ± 2.841 SD, p < 0.01; PDw/oCCE: 1.84 mm ±.778 SD vs. PDw/CCE: 2.06 mm ±.868 SD, p > 0.01). Duct size was not correlated to liver function tests (ASAT, ALAT, GGT). Using quantile regression on the 95th percentile age and gender dependent upper limits for normal duct size were defined (< 70 years PD male 3.77 cm, female 3.76 cm; CBD male 9.16 cm, female 10.70 cm; > 70 years PD male 4.12 cm, female 4.35 cm; CBD male 10.32 cm, female 12.44 cm). PD but not CBD diameters significantly changed after administration of secretin. Upper limits of normal PD size after secretin were (< 70 years PDsec male 4.33 cm, female 4.11 cm; > 70 years PDsec male 5.95 cm, female 4.74 cm).

Conclusions:

Up to 18% of healthy volunteers would have undergone diagnostic workup for enlarged CBD or PD above the current reference standard. The width of the pancreaticobiliary ducts increases in an age dependent manner in asymptomatic volunteers. An increase of the CBD after cholecystectomy can be observed, whereas the PD remains unaffected. In cases of no signs of cholastatic liver disease a moderately increased duct diameter is most likely non pathologic. So to reduce healthcare expenditure and unnecessary workup age and gender related adjustments of the reference values are suggested to avoid unnecessary diagnostic workup.