Utility of the Common Bile Duct

By Michael Prats, MD

CBD byte

Utility of common bile duct measurement in emergency department point of care ultrasound: A prospective study

American Journal of Emergency Medicine November 2017 - Pubmed Link

Take Home Points

1. Common bile duct dilation did not contribute to diagnosing complicated biliary pathology in this study.

2. Dilated common bile duct is only weakly specific for complicated biliary pathology.

3. Wall thickening was the most common sonographic finding in complicated biliary pathology whereas less than 50% had gallstones.


We know that ultrasound is the initial test o’ choice for suspected biliary pathology. We are looking for problems such as gallstones, cholecystitis, cholangitis, and choledocholithiasis. Point of care ultrasound has been shown to be accurate and to expedite the management of the patients who require work up for these diseases. It’s easy enough to see if there is wall thickening, fluid around the gallbladder, and gallstones - but finding the wiley common bile duct can be tricky. Especially when it is a normal size, it can be quite small and difficult to find. Therefore, this article aimed to see exactly how important it was to find and measure the common bile duct. Would there be significant pathology missed if the work up was otherwise not concerning?


Is there utility to measuring a common bile duct (CBD) diameter to diagnose complicated biliary pathology in patients with normal laboratory values and no gallbladder wall thickening, pericholecystic fluid, or sonographic murphy’s sign on POCUS?


Single center, academic institution

Enrolled between Nov 2012 and Sept 2014


  • Patients receiving evaluation for potential biliary pathology in the emergency department (with both laboratory and POCUS of right upper quadrant)


  • Pregnancy, incarcerated

  • Did not consent

  • Did not speak English or Spanish

  • Could not be reached for follow up


Prospective, observational

Patients received laboratory studies and POCUS of RUQ.

Gold standard in determining ultimate diagnosis was the ED or hospital discharge final diagnosis.

2 week follow up to determine any change in diagnosis or further ED visit or hospitalization

Diagnoses classified as one of three possibilities:

  • Non-biliary

  • Uncomplicated cholelithiasis

  • Complicated biliary pathology - any biliary diagnosis necessitating hospitalization for further diagnostic evaluation, definitive treatment (including acute cholecystitis, choledoccholithiasis, cholangitis, and pancreatitis)

Power analysis required sample of 108 patients.


Patients in the ED received standard history and physical. If there was concern for biliary pathology, they were enrolled in study.

They then underwent RUQ POCUS and laboratory testing (at the discretion of treating physician). Blinded to lab results at time of POCUS.

RUQ performed by treating emergency physician.

Data collected from chart: age, gender, BMI, sonographic findings, lab values (alk phos, ALT, AST, total bilirubin, WBC), final diagnosis

Final diagnosis determined from ED discharge documentation or hospital discharge summary, including ERCP results and surgical pathology.

Patients contacted at two weeks for follow up. If not reached, called monthly for 1 year. If still not reached → excluded from study.

Who did the ultrasounds?

Emergency physicians - a total of 26 at various levels of training (resident, fellow, attending)

No study-specific instruction or work shop. All had completed at least 1 hour of didactics and 3 hour of hands on scanning (in basic US training).

The Scan

Curvilinear or phased array transducer


They evaluated for the presence or absence of gallstones, pericholecystitc fluid, sonographic Murphy’s sign, measurement of anterior gallbladder wall, and common bile duct diameter

Considered abnormal if any of these:

Wall thickness > 3 mm

Positive Pericholecystic fluid

Sonographic Murphy’s sign

Common bile duct dilation determined as >6 mm, or if > 60 years of age, then > 1 mm per decade of life

Learn how to scan the gallbladder! - 5 Minute Sono - Gallbladder



Enrolled 167, 9 excluded

N = 158

  • 72.2% female

  • median age 35

  • median BMI 28

  • 48.1% non-biliary diagnoses

  • 51.9% biliary

    • Uncomplicated cholelithiasis 27.2%
    • Complicated biliary pathology 24.7%

      • 8.9% cholecystitis
      • 12% choledocholithiasis
      • 1.3% (n=2) extrahepatic ductal dilation
      • 0.6% (n=1) hepatitis
      • 1.9% (n=3) pancreatitis

63.3% had some abnormal lab

46.2% had gallstones on POCUS

44.9% had some other abnormal US finding

  • Wall thickening 36%

  • Pericholecystic fluid 8.9%

  • Sono murphys 8.9%

CBD not identified in 4.4% (7 patients)

Dilated CBD visualized in 12.7% (20 cases)

Primary Outcome

Patients with complicated biliary pathology

  • abnormal labs 79.5%

  • abnormal pocus 74.4%

  • Gallstones 46.2% (so you can’t just rule out pathology by absence of gallstones)

  • Dilated CBD 23.7%

Only 2 (1.3%) cases of complicated biliary pathology without laboratory abnormality or POCUS abnormality. Neither had CBD dilation.

  • both were diagnosed with choledocholithiasis

  • one had gallstones

Other Findings

Of all of the patients with CBD dilation - 2 (10%) did not have at least one laboratory abnormality, or abnormal POCUS finding besides gallstones.

  • 1 had gallstones, radiology performed US showed signs of uncomplicated cholecystitis

  • 1 is not described in paper but said to not have complicated biliary pathology

Only 1 patient without a visualized CBD had complicated biliary pathology → pancreatitis (had elevated lipase)

So test characteristics for CBD dilation diagnosing complicated biliary pathology:

Sens 23.7%

Spec 90.27%

+LR 2.43

-LR 0.85

Dilated CBD found in 9.7% (11/113) of the uncomplicated or non-biliary diagnoses


Single center, convenience sample

The POCUS findings were not correlated with any standard or expert overview. So perhaps there could have been inaccuracy in POCUS interpretations - this could make the test accuracy results different (could be better or worse). However, this does reflect actual practice because these physicians will be using their own scans to make decisions generally.

Gold standard was discharge diagnosis. Since not every patient received a definitive study (like MRCP or ERCP for example), it is impossible to say that there was not pathology that was missed. However, since ultrasound is known to be fairly accurate for these diseases, this may not have thrown off the results too much.

Average BMI 28. We know that the larger the patient, often the more difficult it can be to obtain good abdominal images.

No cases of cholangitis or malignancy - unclear if these and other etiologies could present with common bile duct dilation without other sonographic or laboratory abnormality.

Instead of calculating the test characteristics of dilated CBD (which everybody suspected were bad), it would have been nice to calculate the test characteristics of [GB thickening, pericholecystic fluid, sonographic Murphy OR abnormal labs] for diagnosing complicated biliary pathology. They obtained the data to do it but not enough information provided in manuscript to calculate it.


Should we still attempt to find the bile duct? Should we still teach others to find the common bile duct? Probably yes to both. Remember that this is just a single study with less than 40 patients with complicated biliary pathology - not enough to hang your hat on. They were able to find the common bile duct in >95% of the cases in this study, so its not as hard as you might think. Although it is unlikely to help you, there is the small chance that it might some day. Everyone should still know how to find it and how to recognize when it is abnormally dilated.

Take Home Points

1. Common bile duct dilation did not contribute to diagnosing complicated biliary pathology in this study.

2. Dilated common bile duct is only weakly specific for complicated biliary pathology.

3. Wall thickening was the most common sonographic finding in complicated biliary pathology whereas less than 50% had gallstones.

Our score

4 Probes

Cite this post as

Michael Prats, MD. Utility of the Common Bile Duct. Ultrasound G.E.L. Podcast Blog. Published on January 15, 2018. Accessed on December 05, 2020. Available at https://www.ultrasoundgel.org/36.
Published on 01/15/18 04:00 AM
comments (2)
By Anonymous on 01/25/18 04:06 PM
great study..........numbers low, but certainly suggests that when one can't find the CBD, and clinical and lab findings don't suggest biliary path, it will be OK to let pt go home and return for further evaluation/workup as needed.
By Mike Prats on 01/26/18 12:02 PM
Thanks for your comment. I agree with you for the most part - the important point is that we are always treating the patient together with the ultrasound findings and not just making decisions based on US alone. If the patient looks bad or you just have a suspicion - you may need to get further imaging or observation. It does seem that not finding the CBD may not play much into the decision making.