Wall echo shadow (WES) triad aka double-arc-shadow sign:

  1. Well-defined near wall
  2. Echoes from stones immediately beneath the wall
  3. Posterior shadowing caused by strong echoes from stones in the gallbladder fossa.

Transabdominal right upper quadrant ultrasound showing the wall echo shadow triad. | Datta, A., Garg, N. & Lema, P.C. The significance of the wall echo shadow triad on ultrasonography: a case series. Crit Ultrasound J 2, 107–108 (2010). https://doi.org/10.1007/s13089-010-0038-z

Transabdominal right upper quadrant ultrasound showing the wall echo shadow triad. | Datta, A., Garg, N. & Lema, P.C. The significance of the wall echo shadow triad on ultrasonography: a case series. Crit Ultrasound J 2, 107–108 (2010). https://doi.org/10.1007/s13089-010-0038-z