Heterogeneity can be either focal or diffuse. The breast echotexture is characterized by multiple small areas of increased and decreased echogenicity. Shadowing may occur at the interfaces of fat lobules and parenchyma. This pattern occurs in younger breasts and those with heterogeneously dense parenchyma depicted mammographically. How and if this pattern affects the sensitivity of sonography merits study, but technical maneuvers may help resolve interpretive issues of true lesion versus pseudopathology.