Which of the following indicates a mass with posterior enhancement in sonography?

A mass with posterior enhancement in sonography is indicative of a cystic structure. Posterior enhancement occurs when a fluid-filled cyst transmits sound more efficiently than surrounding tissues. This results in increased echogenicity behind the cyst, creating a brighter area that is seen on the sonogram. Cystic masses display this characteristic because they contain fluid, which allows ultrasound waves to travel through easily, amplifying the sound reflection from structures that are situated behind the cyst.

In contrast, solid masses do not typically exhibit posterior enhancement as they reflect sound differently due to their dense cellular structure, which does not allow for the same transmission of sound waves. Hyperechoic masses are those that appear brighter than the surrounding tissue but do not specifically indicate whether they are cystic or solid. Similarly, isoechoic masses display the same echogenicity as the surrounding tissue, making it challenging to distinguish their nature without further assessment. Thus, cystic lesions uniquely demonstrate posterior enhancement due to their fluid content, making them the correct choice.