Contemporary concepts in imaging urinary tract obstruction.

Imaging techniques for renal obstruction remain in a continual state of flux. An improved data base has been developed for renal ultrasonography, permitting a more precise evaluation of hydronephrosis. Rigidity with regard to an algorithm for renal obstruction is not recommended because it would be fixed at a point in time and dependent upon the equipment and expertise of a given institution. In all likelihood ultrasonography will continue to be used as the primary screening tool. A role for the intravenous urogram remains, especially in the acute presentation of renal obstruction. It is interesting to note that the initial description of the percutaneous nephrostomy tube was as a diagnostic technique in patients who had long-standing ureteropelvic junction obstruction. Prediction of recoverability of the kidneys was not possible without relieving the obstruction and assessing the ability of the postobstructive kidney to function. Recoverability of renal function cannot be assessed on a short-term basis but takes time. Up to 8 weeks is necessary before the kidney has established its new baseline level of function. The percutaneous nephrostomy has become an integral tool for the interventional radiologist and is used in treatment. Indeed, its treatment role is important, and even today we must be careful not to assess the kidneys' functional status after placement of the nephrostomy tube without allowing the renal unit sufficient time for recovery. The future undoubtedly will bring further tremendous changes in our assessment of renal obstruction. It is important that radiologists position themselves at the forefront of these developments.