Tomography of the kidney bed as an aid in differentiating renal pelvic tumor and stone.

Plain film tomography is of value in detecting small amounts of calcium in "non-opaque" stones. The use of this technique to help differentiate renal pelvic tumor from stone in patients presenting with a filling defect in the renal pelvis is suggested. Four cases in which plain film tomography detected calcium in a renal pelvic stone that could not be seen on routine roentgenograms are presented.