Infiltrative renal lesions: CT-sonographic-pathologic correlation.

The CT and sonographic findings in 23 cases of renal lesions in which the abnormality was infiltrative, as opposed to expansile, were analyzed (invasive transitional cell carcinoma [seven], renal lymphoma [six], metastasis to the kidney [three], acute bacterial nephritis [three], mesoblastic nephroma [two], squamous cell carcinoma of the renal pelvis [one], and renal cell carcinoma [one]). CT scans were evaluated for shape and density of the mass, pelvocaliceal displacement, effect on the renal sinus fat, and the presence of perirenal involvement. Sonograms were evaluated for the shape and echogenicity of the mass and for the effect on the renal sinus echoes. Findings of infiltrative growth included poorly defined margins of the mass; trapped, nondisplaced infundibulae; and calices with occasional calicectasis, diminished contrast enhancement, occasional nephrographic striations, replacement of central sinus fat, loss of central sinus echoes, and variable renal parenchymal echogenicity. The reniform shape was usually preserved and was present in 19 of 20 cases with CT and 13 of 15 cases with sonograms. These observations indicate that analyses of the margins, architecture, and effects on the collecting system and renal sinus by the mass are helpful in the diagnosis of those diseases that characteristically infiltrate the kidney.