The hyperechoic region results from which mechanism?

• A. Increased Acoustic Velocity Through a Fluid-Filled Structure
• B. Decreased Attenuation Through a Fluid-Filled Structure
• C. Decreased Sound Absorption in the Region Distal to the Fluid-Filled Structure
• D. High Acoustic Impedance Mismatch

Answer: (B)

The main idea is how fluids affect ultrasound transmission and brightness. Fluids attenuate the beam less than surrounding tissues, so more of the ultrasound energy reaches tissues distal to the fluid. The echoes from those deeper tissues return stronger signals, making the area behind the fluid appear brighter—posterior acoustic enhancement. This is why a hyperechoic region forms due to decreased attenuation through a fluid-filled structure.

A stronger boundary reflection (high impedance mismatch) can create a bright line at the interface, but it doesn’t explain the bright region behind the fluid. Increased velocity changes timing, not brightness, and the concept of decreased absorption distal to the fluid isn’t the standard explanation for this posterior bright region.