Which feature characterizes a fluid-filled cyst on ultrasound?

• A. Hypoechoic appearance
• B. Anechoic appearance
• C. Hyperechoic appearance
• D. Complex structure

Answer: (B)

A fluid-filled cyst on ultrasound is characterized by an anechoic appearance. This means that the cyst appears completely dark on the ultrasound image, as it does not reflect any sound waves. The reason for this anechoic appearance is that fluids, such as those found in simple cysts, do not contain significant internal structures or echoes, allowing them to transmit ultrasound waves without scattering them significantly.

In contrast, features like hypoechoic (which would suggest low-level echoes due to some internal content or thicker walls), hyperechoic (indicating a structure that reflects sound waves well and appears bright), or a complex structure (suggesting mixed echogenic characteristics often indicative of solid and cystic components) do not accurately represent the nature of a fluid-filled cyst. Simple cysts are defined by their very clear, anechoic nature, making it easy for sonographers to identify them during an ultrasound examination.