One of the most common complaints I hear from my residents is that they can never find the common bile duct. Unlike more complicated bedside ultrasound tasks such as getting the perfect apical four chamber, this seems to be the source of much frustration that does not reliably seem to improve with practice.
Full disclosure: I can relate. I am a champion RUQ scanner. I can always find the gallbladder, no matter how contracted or how hidden it is under layers of soft tissue. But I admit that there were a few patients in which the CBD went unmeasured because I just couldn't confidently identify it. I'm not alone; it's not uncommon to open a formal scan and find an image labeled “CBD???” by the tech.
What does that mean for the frustrated sonographer who can't find the CBD? One of my favorite blogs (and podcasts), Ultrasound Gel (ultrasoundgel.org), recently analyzed this topic (http://bit.ly/2tISgdT), and a prospective observational trial published last year sought to evaluate whether a bedside CBD measurement contributed to the diagnosis of significant biliary pathology, particularly when labs and other ultrasound findings were normal. (Am J Emerg Med 2017. doi: 10.1016/j.ajem.2017.10.064.)
The study enrolled 158 patients who presented to the ED with complaints concerning for a biliary source based on history and physical exam. All of these patients underwent lab testing and a bedside ultrasound, which looked for gallstones, gallbladder wall thickening, pericholecystic fluid, sonographic Murphy's sign, and a measurement of the CBD. The gold standard for comparison was the diagnosis at discharge, which could have been based on further testing like CT scan or inpatient workup or on ED findings (bedside ultrasound alone versus further imaging).
Here's the good news: An isolated dilated common bile duct with an associated diagnosis of complicated biliary pathology is rare. All of the patients with complicated biliary pathology and a dilated CBD in this study had other findings such as abnormal labs.
Interestingly, two patients had neither abnormal labs nor a dilated CBD, and were ultimately diagnosed with choledocholithiasis and pancreatitis. These patients had other findings (gallstones and an additionally ordered lipase) that led to the diagnosis. Clearly, the examiners were not satisfied with their initial evaluation based on the presentation of the patient and kept looking.
Context is crucial, as with everything else in medicine. A sick-appearing patient with a normal ultrasound and normal labs needs further evaluation, whether or not I can find the CBD. This study lends credence to the idea that an otherwise normal ultrasound and normal labs can be reassuring when the CBD proves elusive.
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