Diagnostic and functional implications of pelvocalyceal system nonvisualization on [99m]Tc-DTPA renal images

Most functional abnormalities observed on 99mTc-DTPA renal images probably reflect GFR changes and the functional consequences of these changes. We have noted an unexplained failure of the pelvocalyceal system to visualize in some patients during the renal imaging sequence. This led us to study the relationship between pelvocalyceal nonvisualization and GFR, and to search for plausible explanations of the absent visualization. In 41 patients with combined renal imaging and GFR determinations, pelvecalyceal nonvisualization was seen only with GFR values below 20 ml/min. The sign was 100% sensitive and 100% specific predicting GFR less than 20 and serum creatinine above 2.9 mg/dl. In vitro studies revealed markedly reduced amounts of DTPA chelate in the urine of patients with GFR less than 20, but in addition they had decreased tubular water reabsorption leading to dilution of the already reduced urine chelate contents. The reduced amounts of 99mTc-DTPA per ml of pelvocalyceal urine may account for the nonvisualization of this system. It may be that the intensity of the pelvocalyceal system reflects the adequacy of both the GFR, and the water reabsorptive function of the renal tubules.