Radiolucent filling defects of the renal pelvis: classification and report of unusual cases.

Eight cases of unusual radiolucent filling defects in the renal pelvis and calices are reported. With reference to the literature and these cases, such defects have been classified etiologically as tumors, calculi, blood clots, air bubbles, congenital anomalies, vascular phenomena, infections and associated conditions, foreign bodies and miscellaneous conditions. Most of these conditions are rare but their accurate delineation with modern diagnostic techniques will allow for more conservative surgical procedures and for maximal preservation of renal substance.