Contemporary concepts for imaging urinary tract obstruction

Acute urinary tract obstruction. Imaging update

Although urinary tract obstruction is an age old problem with IVU the time-honored imaging technique of choice, recent advances in renal ultrasonography and abdominal and pelvic CT scanning have advanced these alternative modalities to the forefront. No rigid algorithm for renal obstruction is recommended, because the utilization of these techniques is in a state of flux. The use of one modality over another as a first-line imaging technique likely will depend on the equipment availability and expertise of a given institution. The choice also may be guided by each institution's cost of each type of examination. Although a role for the IVU remains in the evaluation of acute renal obstruction, ultrasonography and CT scan have emerged as alternative primary screening tools. Undoubtedly, the future will bring further changes in our assessment of renal obstruction. The cost effectiveness and definitiveness of evaluation likely will become more important driving factors than they have been in the past. The radiologist and urologist together must assess available imaging techniques, their effectiveness, and the institution's expertise to develop a cost-effective and efficient system for assessment of renal obstruction.

Renal resistive index in experimental partial and complete ureteral obstruction

RATIONALE AND OBJECTIVES

Recent clinical work suggests that the Doppler resistive index (RI) may be useful in distinguishing obstructive from nonobstructive hydronephrosis. We evaluated the usefulness of the RI in a rabbit model of hydronephrosis.

METHODS

Unilateral partial ureteral obstruction was produced in nine rabbits and complete obstruction in another nine. Three sham operations were performed, and these animals served as control subjects. The RI was measured in all kidneys before and 6 hr after surgery and on days 1, 4, and 7 postoperatively. The RI and the difference in RI (delta RI) between the obstructed and normal kidney were evaluated over time using a two-way analysis of variance. The intravenous urography and Whitaker tests served as gold standards.

RESULTS

Hydronephrosis was observed on sonograms in all obstructed kidneys. Comparing groups, there was no significant difference in mean RI or delta RI between the three groups at any time point. Looking at individual groups over time, there was no significant change in mean delta RI, whereas the change in mean RI was significantly elevated above baseline only in the complete obstruction group at 6 hr (p = .002) and on days 4 (p = .008) and 7 (p = .006). In evaluating varying thresholds of RI and delta RI, we could not consistently discriminate between normal and obstructed kidneys.

CONCLUSION

Although complete obstruction caused a significant increase in RI, partial obstruction failed to do so. RI and delta RI values proved to be insensitive predictors of obstruction in this rabbit model.

Doppler sonography in congenital ureteropelvic junction obstruction and multicystic dysplastic kidneys

The accurate diagnosis of severe congenital ureteropelvic junction obstruction (UPJO) and the indications for surgical intervention are a matter of debate. Differential diagnosis from, for example, congenital cystic kidney malformations is important. In the present study we analysed the value of Doppler sonography (DS) for assessment of obstruction in congenital UPJO and its usefulness for differential diagnosis. A total of 138 infants and children were examined. Forty-three healthy infants and 24 children who had had a pyeloplasty at least 1 year previously served as control groups. Seventy-one children with UPJO and cystic kidney malformations underwent DS in addition to the usual examinations of intravenous urography and scintigraphy. Resistive Index (RI) was measured in both kidneys. Twenty infants showed decompensated UPJO and had needed an operation. Preoperatively all showed significantly increased RI (RI = 74%), which returned to normal after operation (RI = 68.3%). Thirty-nine children with UPJO could be managed conservatively, showing compensated obstruction on diuretic renography. On DS they had normal and symmetrical RI values (RI = 67%). Eleven children had multicystic dysplastic kidneys; 4 underwent nephrectomy. On DS all showed either absence of perfusion signals or very low flow velocities with very high RI values (RI = 90-100%) in the renal vessels. One child was found to be suffering from a cystic nephroma. DS was able to reveal quite normal vessel distribution in renal parenchyma with slightly elevated RI values (RI = 80%). Our results indicate that DS a non-invasive, non-ionising method of investigation, may serve as an additional functional parameter for defining accurately the degree of obstruction in UPJO.(ABSTRACT TRUNCATED AT 250 WORDS)