how to measure cbd on ultrasound

How to measure cbd on ultrasound

It is an established fact that variations exist in the anthropometric features of various populations, races and regions [4]. Studies have suggested correlation between different kinds of body builds and diseases. However, despite technological advancements, the association of anthropometric measurements with the diameters of common bile duct has remained controversial.

We conducted this study to obtain data on sonographically measured diameters of common bile duct among Rajasthani population in order to determine the range of normal diameters for common bile duct among this population and to determine its association with age, sex, physical measurements like height, weight, chest circumference, circumference at the transpyloric plane, circumference at the umbilicus and circumference at the hip.

Abstract

The mean diameters of the common bile duct in the three locations were: proximal, 4.0 mm (SD 1.02 mm); middle, 4.1 mm (SD 1.01 mm); and distal, 4.2 mm (SD 1.01 mm). The overall mean for all measures was 4.1 mm, with a standard deviation of 1.01 mm. All the three diameters were highly correlated and statistically significant (p-value<0.001). While the lower limit of common bile duct diameter among the normal subjects was 2.0 mm, the upper limit was found to be 7.9 mm. However, 95% of the study participants showed a common bile duct diameter of < 6 mm.

Introduction

Ultrasonographic measurement of CBD at three locations

How to measure cbd on ultrasound

Becker, B. A., E. Chin, E. Mervis, C. L. Anderson, M. H. Oshita and J. C. Fox (2014). “Emergency biliary sonography: utility of common bile duct measurement in the diagnosis of cholecystitis and choledocholithiasis.” J Emerg Med 46(1): 54-60. PMID: 24126067

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5 Minute Sono Video

Generally, a curvilinear probe is preferred, although a phased array probe may also be used.

References

Miettinen, P., P. Pasanen, J. Lahtinen and E. Alhava (1996). “Acute abdominal pain in adults.” Ann Chir Gynaecol 85(1): 5-9. PMID: 8739926

Evaluation

Her pancreas was seen to be swollen. The enlargement of the pancreas
may have various causes and if a biliary stone is lodged in the distal
CBD then the patient may develop pancreatitis. With aging, the pancreas
becomes more echogenic and atrophic on ultrasound.

Her biliary tree is dilated with both intrahepatic and extrahepatic
biliary dilatation. Her CBD measured 11 mm. This is a pathologically
dilated CBD. In over 95% of young normal subjects the common bile duct
measures less than 4mm. In the presence of gallstones the CBD can measure
up to 7mm without implying obstruction. The CBD can also dilate in the
elderly secondary to degeneration in the ductal wall and reach diameters
of up to 9mm. The CBD can also change in size physiologically in relation
to meals. In this patient there were gallstones readily visible in the
lower CBD on ultrasound. A diameter of the CBD of over 10mm is definitely
abnormal and will suggest the presence of stones in the CBD. In assessing
the CBD for stones, if ductal stones are seen then stones are present. If
CBD stones are not seen then this does not mean that they are absent since
there is a significant rate of false negative results, partly related to
the presence of obscuring gas in the duodenum.

Her initial presentation was during a consultation made by her
husband. Her symptoms seem relatively minor yet the biochemistry results
are quite abnormal indicating a pattern of obstructive jaundice. Her
ultrasound findings are dramatic with stones seen in the gallbladder and
in the lower common bile duct (CBD). Ultrasound is the first-line
investigation for the gallbladder and biliary tree. The ultrasound scan
should be available with only a short wait for more urgent cases. This
patient should be prioritised for an urgent scan appointment.

The appearances of the liver are unexplained. Ultrasound is good for
assessing focal liver disease. A common abnormal pattern is the
geographical echogenic appearance seen in fatty change of the liver.

The relationship to ‘pathology’ seen on imaging to ‘disease’ and
clinical symptoms is interesting. Gallstones are common and an incidence
in excess of 10% in the population is described. It is common to find
gallstones in an otherwise asymptomatic patient. My policy is to tell
patients that they have gallstones even if they have no symptoms, however
I am always concerned that patients will then develop symptoms. I am
always surprised how patients can have significant radiological pathology
and have so few symptoms. The patient had obvious gallstones, a thickened
gallbladder wall, biliary dilatation and many CBD stones and yet had only
itching with a history of itching. The story of painless jaundice would be
more suggestive of pancreatic malignancy or a drug reaction rather than
gallstones.

Competing interests:
I am a commentator on this interactive case and will receive an honorarium from the BMJ. I am a radiologist working in the same hospitals that the patient attended.