Differential diagnosis of hypoechoic and anechoic masses with gray scale sonography: new observations.

With the technological advances in gray scale sonography that have permitted the use of higher-frequency transducers and expansion of the acoustic dynamic range, increasing problems in differentiating solid masses and fluid-filled masses have become apparent. These difficulties can be overcome by strict adherence to proper scanning techniques, which involve transducer selection, tissue attenuation compensation, and alterations in patient position. The availability of variable-dynamic-range signal processing and the use of real-time scanning can further increase one's confidence in the correct interpretation of these masses. The primary criteria for determining that a mass is fluid-filled have been expanded to include the presence of reverberation echoes, the "lateral shades" sign, and the presence of septations. In the past, hypoechoic masses with low-level internal echoes were termed "complex". Both fluid-filled masses and solid masses may fall into this category. By use of the sonographic criteria, an attempt should be made to determine whether a mass is primarily fluid-filled or solid. Specific anatomic locations and pathologic conditions in which differential diagnosis may be difficult are illustrated; these include abdominal masses, hepatic and renal masses, and pelvic masses.