Does incidentally detected common bile duct dilation need evaluation?

WHAT CONSTITUTES BILE DUCT DILATION?

There is no absolute measurement that defines common bile duct dilation, but a dilation of 7 mm or greater is generally accepted as the cutoff for clinical and research purposes. It is important to note that measurement ranges for dilation vary based on the imaging modality, site of measurement along the duct, and patient factors (eg, age, history of cholecystectomy). The upper limit of normal for common bile duct diameter is 6 to 8 mm when measured with transabdominal ultrasonography, and 8 to 10 mm with CT.¹ To adjust for age, adding 1 mm to the measurement per decade of life after age 60 or 0.4 mm for each decade of life has been proposed, although the evidence varies.¹ After cholecystectomy, asymptomatic common bile duct dilation of up to 10 mm has been reported to be within normal range.² Given the challenges to defining specific dilation values, the decision to pursue further diagnostic testing should be based on the likelihood of underlying obstructive vs nonobstructive causes.

CLINICAL EVALUATION

Specific elements of the patient’s history, physical examination, and biochemical markers can help determine if biliary obstruction warrants further investigation (Table 1). Clinical symptoms such as jaundice, steatorrhea, acholic stools, dark urine, pruritus, and weight loss can reflect obstructive causes, which may include malignancy. The combination of fever, abdominal pain, and jaundice (Charcot triad) suggests ascending cholangitis, which occurs more commonly with choledocholithiasis than with malignancy in the absence of a previous biliary procedure such as ERCP.¹ Acute onset of symptoms including pain is typical of choledocholithiasis, whereas gradual weight loss and jaundice (often painless) suggest a malignant process.

Abnormal liver biochemistry results including elevation of total or direct serum bilirubin, alkaline phosphatase, aspartate aminotransferase, and alanine aminotransferase can indicate an obstructive cause and should be evaluated. To some degree, these levels can be elevated in the setting of common bile duct obstruction, depending on the cause, extent, and chronicity of disease. Moreover, imaging with EUS is more likely to reveal a cause for dilated common bile duct in patients with elevated liver biochemistries than in those without (53% vs 6%), highlighting the importance of testing for these abnormalities.⁶ Although this article focuses on evaluating incidental common bile duct dilation, if abnormal liver biochemistries persist after an appropriate workup for bile duct dilation (see discussion below), further assessment is needed in accordance with published guidelines⁷ and in consultation with gastroenterology and hepatology specialists.

If there are no concerning clinical or biochemical findings for obstruction and there is no explanation for nonobstructive dilation such as older age, previous cholecystectomy, or opioid use, imaging should be done to exclude features suggestive of an infrequently encountered subclinical or impending obstructive process. These include a concurrently dilated pancreatic duct (the “double-duct sign”), which could indicate a pancreatic or ampullary tumor; an appreciable intraductal biliary stone or lesion suggesting choledocholithiasis; intrahepatic duct dilation (≥ 1–2 mm); moderate to severe extra-hepatic bile duct dilation (≥ 10 mm), or an abrupt cutoff of the common bile duct dilation.^1,8 If available, prior imaging (including an intraoperative cholangiogram performed during cholecystectomy) should also be reviewed as a new or progressive dilation may be more concerning than a chronic stable dilation.

In the absence of the above findings, mild ductal dilation may be benign, especially in patients who are over age 60, have undergone cholecystectomy, or use opioids, and does not warrant further evaluation. Studies have shown that further diagnostic testing of incidentally found asymptomatic ductal dilatations without clinical or biochemical abnormalities has very low diagnostic yield,⁹ but it is a potential area for research.¹⁰

IMAGING OPTIONS FOR WORKUP

If a common bile duct dilation is identified and the decision is made to pursue further workup, the next step is to determine which imaging modality to use. The most commonly used options are described below.

CLINICAL APPROACH TO THE EVALUATION

For a patient with potential incidental bile duct dilation, there are 4 general clinical decision-making pathways, as follows (Figure 1)^1,3:

• Common bile duct dilation (ie, ≥ 7 mm on ultrasonography or ≥ 10 mm on CT) with clinical or biochemical features of obstruction warrants further investigation. ERCP is the initial choice if there are signs of ascending cholangitis. If there are no signs of ascending cholangitis, MRCP with contrast or EUS is indicated, and if these imaging results are positive for obstruction, EUS for biopsy with or without ERCP for drainage is needed.

• If there is dilation but no clinical or biochemical signs of obstruction, and if the patient has risk factors for nonobstructive dilation (eg, older age, previous cholecystectomy, opioid use), no further workup is warranted. But if the patient has no risk factors for nonobstructive dilation, then pursue MRCP with contrast or EUS.

• If the common bile duct diameter is normal (ie, < 7 mm on ultrasonography or < 10 mm on CT) but there are clinical or biochemical signs of obstruction, further evaluation is warranted. If there are signs of ascending cholangitis, an ERCP is indicated. If there are no signs of ascending cholangitis, MRCP with contrast or EUS is indicated. If either imaging test shows an obstruction, EUS for biopsy with or without ERCP for drainage is needed.

• If the bile duct diameter is normal and there are no clinical or biochemical characteristics of obstruction, further evaluation is not indicated.

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FIGURE 1

Clinical approach to incidental bile duct dilation.

CT = computed tomography; ERCP = endoscopic retrograde cholangiopancreatography; EUS = endoscopic ultrasonography; MRCP = magnetic resonance cholangeopancreatography

Based on information in reference 1.

If EUS or ERCP is warranted or if there is uncertainty regarding the workup of bile duct dilation, the patient should be referred to a gastroenterologist.

TAKE-HOME POINTS

Once identified, incidental common bile duct dilation can be categorized as nonobstructive or obstructive. Clinical, biochemical, and imaging findings should guide the decision-making regarding further evaluation or intervention. MRCP with contrast and EUS can provide an accurate and minimally invasive diagnostic evaluation, while ERCP is best reserved for patients who require therapeutic intervention.

DISCLOSURES

Dr. Sethi has disclosed consulting for Boston Scientific, Fujifilm, Interscope, Medtronic, and Olympus America. The other authors report no relevant financial relationships which, in the context of their contributions, could be perceived as a potential conflict of interest.