Why do cystic structures show posterior enhancement?

• A. They reflect more energy, causing brightness behind
• B. They scatter energy, reducing brightness behind
• C. They have low attenuation, allowing more energy to pass, increasing brightness behind them.
• D. They cause refraction that shifts the image

Answer: (C)

Posterior enhancement happens because fluid-filled cysts have very low attenuation. The ultrasound beam passes through the cyst with minimal energy loss, so more sound energy reaches the tissues behind it. Those deeper tissues then return stronger echoes, making the area directly behind the cyst appear brighter on the image. In contrast, more attenuating or solid structures absorb or scatter more energy, reducing transmission and often causing shadowing rather than enhancement.