Unfortunately many, if not most, abscesses do not fulfill the criteria for "typical" fluid collections. Because they frequently contain particulate material or are loculated, it is not unusual for abscesses to have internal echoes. In addition, their walls are frequently irregular or thickened and lack sharpness. Finally, the fluid in some abscesses may actually attenuate sound, in which case transmission will be poor.

There is no such thing as a "typical" ultrasonographic pattern for an abscess. The spectrum ranges from purely cystic to solid. They may have both echo-free and echo-producing regions, the latter being either diffuse or sludgelike, or coarse and clumped. Some infected fluid collections contain linear echoes due to membranes, septae, or internal layering of different components causing fluid-fluid levels. Totally echogenic abscesses may occur because of gas-producing organisms which cause highly echogenic microbubbles. Occasionally, however, as in the example shown in the left lobe of this patient's liver, a highly echogenic abscess can be present without gas being responsible.