Endoscopic Ultrasound in CBD Stone
Article Outline
- Answer to the Clinical Challenges and Images in GI Question: Image 4: Comet Tail Artifact in Common Bile Duct Stones
- References
- Copyright
Question: A 40-year-old woman complained of recurrent episodes of right upper quadrant pain. Liver function tests were normal. An abdominal ultrasound revealed a dilated common bile duct (CBD). Computed tomography (CT) confirmed the dilatation of CBD without any intrahepatic bile duct dilatation. Gallbladder was normal. Magnetic resonance cholangiopancreatography also revealed a dilated CBD. An endoscopic ultrasound (EUS) examination was performed with EG3630 UR Pentax echogastroscope (Figure A). What is the diagnosis?
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Answer to the Clinical Challenges and Images in GI Question: Image 4: Comet Tail Artifact in Common Bile Duct Stones
EUS showed a tubular fluid filled choledochal cyst 4 cm long and 1.4 cm in diameter with a smooth wall. The cyst was followed in continuity upward to the origin of the cystic duct and gallbladder (Figure A). Multiple echogenic objects were noted in the cyst. These objects created three different effects in the images. The first and most common effect was acoustic shadowing, which confirmed the echogenic objects as stones (Figure C). The second effect was sludge ball–like shadows (Figure B). The third effect of a “comet tail artifact” was especially noted in the fluid-filled part of the cyst (Figure D). When continuous color Doppler was applied, part of the inferior vena cava behind the CBD stone showed both comet tail artifact and acoustic shadow (Figure C). Comet tail artifacts have been observed in the gallbladder lumen after extracorporeal shock-wave lithotripsy of radiolucent calculi.1
Two varieties of comet tail artifacts have been described: the long variety, which extends to the edge of the screen, and the short variety, which trails off in intensity after a short distance.2, 3 In this case, EUS showed comet tail artifacts of short variety along with the presence of partial acoustic shadow. The simultaneous presence of comet tail artifact and acoustic shadow can be explained by ultrasound energy reflection at different interfaces. The ultrasound energy from the ultrasound probe passed through 3 media with different acoustic impedance values (Figure E). Two acoustic interfaces were created in the presence of these media, the first between soft tissue and stone in choledochal cyst, and the second between the stone and the fluid filled part of cyst. Energy was partly reflected from the first interface, partly transmitted through the stone at the second interface and remnant energy reverberated inside the stone. The partial reflection gave rise to incomplete acoustic shadow, the partial transmission caused faint visualization of the area beyond the stone, and the reverberations inside the stones produced a comet tail artifact (Figure E).
References
Conflicts of interest The authors disclose no conflicts.
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PII: S0016-5085(09)00163-2
doi:10.1053/j.gastro.2009.01.059
© 2009 AGA Institute. Published by Elsevier Inc. All rights reserved.
