Infiltrating neoplasms of the kidney.

Some neoplastic processes which involve the kidney develop not as a distinct localized mass, but rather as an infiltrating process which replaces the renal parenchyma, causes little or no mass effect, and contains little if any neovascularity. These neoplasms include (1) carcinoma of the renal pelvis when it invades the parenchyma (transitional cell and squamous cell); (2) blood-borne metastatic squamous cell carcinoma to the kidney (most frequently from the lung): (3) renal lymphoma of the infiltrating variety; and (4) infiltrating sarcomatous type of hypernephroma. While the urographic and angiographic appearance of these infiltrating lesions can be similar, clinical aspects are usually sufficient to differentiate them. Radiographic findings include amputation of portions of the collecting system on urography and encasement of vessels with a loss of nephrogram on angiography.