What causes the WES sign on ultrasound of the gallbladder?
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Answer:
The wall-echo-shadow or WES sign is the triad seen when a gallbladder is completely filled with stones: a curved echogenic line from the gallbladder wall, a thin anechoic line of residual bile, a second, brighter echogenic line from the anterior surface of the stones, and a dense posterior acoustic shadow that obscures everything behind. Recognising it matters because a contracted, stone-packed gallbladder is easily mistaken for bowel gas, and the diagnosis of cholelithiasis can be missed entirely when no lumen is visible. The differentiating features from gas are that shadowing from stones is clean and sharply defined, whereas gas produces dirty shadowing with reverberation and comet-tail artefacts, and stones move with position change. The other entity that shadows in the gallbladder fossa is the porcelain gallbladder, in which the wall itself is calcified; it produces the double-arc shadow sign and is distinguished on CT, which shows mural calcification, and it has a recognised though smaller than once believed association with gallbladder carcinoma. An emphysematous gallbladder with intramural gas gives the effervescent gallbladder appearance with dirty shadowing and is a surgical emergency. When shadowing prevents assessment, CT or MRI with MRCP is used to evaluate the wall, the ducts and any complication.
Why is it called so?
The abbreviation stands for wall, echo and shadow, the three components of the appearance in sequence.
Pathophysiology
Ultrasound reflects almost entirely at interfaces of very different acoustic impedance. When the gallbladder is packed with calculi, the first strong reflection comes from the wall, the small amount of bile trapped between the wall and the stone surface produces a thin anechoic band, and the stone surfaces then reflect the great majority of the remaining beam, so almost no energy travels deeper and a clean anechoic shadow results. Because the stones absorb and reflect rather than scatter the sound, the shadow has sharp margins, in contrast with gas, which scatters sound in many directions and produces reverberation artefacts within a poorly defined shadow. This physical difference is the basis for distinguishing the two.
Alternative names: Wall-echo-shadow complex; double-arc shadow sign when the wall is calcified
Other associated named signs: Double-arc shadow sign of porcelain gallbladder and the effervescent gallbladder of emphysematous cholecystitis
References
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