What does hypoechoic mean in sonography?

In sonography, the term hypoechoic is used to describe a tissue or structure that appears as a darker shade of gray compared to the surrounding tissues on the ultrasound image. This occurs because hypoechoic tissues reflect fewer ultrasound waves back to the transducer, resulting in less echogenicity and a darker appearance. Hypoechoic areas are often indicative of fluid-filled structures or certain types of solid masses, which may not produce as strong echoes as adjacent more echogenic tissues, such as homogeneous organs or other denser structures.

Understanding this concept is crucial in sonography, as it helps in the differentiation of various pathologies and anatomical structures based on their echogenic properties. For example, a hypoechoic mass could raise suspicion for a cyst or tumor in clinical evaluation. This contrasts with other terms like isoechoic (similar echogenicity) or hyperechoic (brighter regions), which describe different levels of echogenicity and corresponding tissue characteristics.