Echogenicity: analysis, significance, and masking.

Echogenicity can be created by the admixture of any acoustically dissimilar substances. Experiments performed in vitro using mineral oil and water and in vivo examining 24 pathologically proven echogenic abnormalities show that echogenicity cannot be ascribed to a specific tissue, but rather is a property of all substances. In addition, when dissimilar histologic and pathologic substances have similar echo appearances and are adjacent, they become indistinguishable. This loss of structural definition can be termed the sonographic "masking sign," comparable in masking qualities to the established radiographic "silhouette sign." When this phenomenon occurs, an abnormality can be detected only through displacement of an organ or distortion of its internal anatomy. A thorough understanding of echogenicity and the sonographic masking sign will allow a more accurate evaluation of masses and infiltrating processes.