Problematic renal masses in ultrasonography and computed tomography.

The diagnosis of renal masses is based upon the contribution of ultrasonography (US) and computed tomography (CT), which enable the recognition of these lesions with high diagnostic accuracy. However, a number of diagnostic difficulties exist in the definition of the nature of the mass, both for cystic and solid lesions, and to a lesser extent in the identification of the mass. "Complicated" cystic masses, such as calcified cysts, hemorrhagic cysts, inflammatory cysts, abscesses, and cystic tumors may be difficult to diagnose with US and sometimes with CT. CT is helpful in most of these cases because it enables the evaluation of the calcifications and the density of the fluid content. CT is also helpful in cases of cystic tumors because it shows the enhancement of septae within the masses. Problems with solid masses are the identification of small renal tumors and the definition of the benign or malignant nature of the mass. Although both techniques enable the recognition of most tumors, even if small in diameter, they are still limited in defining the pathological structure of the tumor.