The fluid cannot disappear completely after kidney surgery because the surgery only fixes the stenosis, but the part above the stenosis that is enlarged by the fluid still exists and has not been trimmed off by the surgery, just like a balloon cannot be restored to the state it was in when it was not blown up and then deflated. Since the kidney produces several hundred milliliters of urine every day, after the narrow area is trimmed, the original enlarged area can be slightly smaller than before the surgery or remain as it is, but if the surgery is not effective, the fluid will continue to grow. The most accurate way to determine the effectiveness of the surgery is the diuretic nephrogram, which initially shows a slow excretion of the tracer concentration, and a rapid excretion of the tracer after the injection of diuretics, indicating a good surgical result, otherwise the tracer does not excrete and the concentration graph continues to rise instead of falling.