The various possibilities offered by isotope studies in [human] cases of obstruction of the upper urinary tract are described. This examination allows the exploration of the dilatation itself, and the isotopic study of renal function. The dilatation can be explored either by means of the nephrogram with hyperdiuresis or by measurement of the renal transit time. The nephrogram with hyperdiuresis will give a precise answer: definite obstruction or no obstruction. Intermediate forms are possible, in which a mathematical interpretation of the curves of decay of the renal radioactivity will help distinguish between hyptonia without obstruction and true obstruction with dilatation. A marked decrease in renal function or severe vesico-renal reflux can interfere with the interpretation of these curves. Measurement of the renal transit time with the mathematical calculation of deconvolution is a valuable application of isotopes, but it is less practical than the nephrogram with hyperdiuresis. The isotope study of renal function is a promising technique, as it is able to study the global clearance without the need for blood tests (this is true for both the glomerular filtration rate and for the measurement of renal blood flow). Furthermore, this technique should allow each kidney to be studied separately. Separate measurements do not provide an absolute value for each kidney, but evaluate the part played by each kidney in the global renal function, which can be measured simply by means of the isotope study. The study of DMSA [dimercaptosuccinate] uptake provides a detailed map of the functioning renal parenchyma, but the DTPA isotope scan provides the maximum information about the nature of the dilatation of the upper urinary tract as well as the global renal function and the separate function of each kidney. The direct measurement of intra-pyelic pressures by percutaneous nephrostomy, Whitaker''s test, apparently is only indicated when the isotope study fails to distinguish between obstruction and dilatation. DTPA, therefore, appears to be the isotope of choice in the investigation of obstructive uropathy.
