Renal resistive index in experimental partial and complete ureteral obstruction

Color Doppler Ultrasonography in Evaluating the Outcomes of Pyeloplasty in Ureteropelvic Junction Obstruction

Purpose

To evaluate the accuracy of Color Doppler ultrasonography for diagnosing post pyeloplasty elimination of obstruction in Ureteropelvic Junction Obstruction patients.

Methodology

Patients with the diagnosis of UPJO enrolled in the study and underwent open pyeloplasty. Three to 6 months after the operation, patients were recalled and underwent isotope scan as the gold standard test and renal color Doppler ultrasonography to assess the success rate of pyeloplasty.

Results

A total of 39 patients were evaluated and analyzed. The average follow-up time for patients was 9.1 months. The success rate of surgery in the study population was 100%. The mean RI of the affected side before the operation was 0.69 ± 0.01 and after the pyeloplasty, it reached to 0.65 ± 0.01. The difference between the mean RI of the affected side before and after the operation is 0.04 (P < 0.001). Age, type and severity of obstruction and the technique of surgery did not have any impact on these parameters. The difference between the RI of the affected and healthy side was termed ΔRI. ΔRI before and after the operation was 0.084 and 0.014, respectively. The decrease of ΔRI in the case of pyeloplasty is 0.07 on average (P < 0.001), which can be predicted for pyeloplasty success.

Discussion

Color Doppler ultrasonography can be used as a non-invasive, fast, non-expensive, and available modality for evaluating the outcome of pyeloplasty instead of the nuclear scan or IVP.

How may Doppler indices help in the differentiation of obstructive from nonobstructive hydronephrosis?

Background:

We assess the potency of different Doppler indices in the differentiation of obstructive and nonobstructive hydronephrosis.

Materials and Methods:

In this study, infants and children who were referred for the evaluation of unilateral hydronephrosis were enrolled. Ultrasonography for the assessment of the degree of hydronephrosis and a voiding cystourethrogram for the exclusion of vesicoureteral reflux was performed. Then, Doppler ultrasonography was done for both kidneys of each patient using four classic Doppler indices as well as the difference (delta) of each index between to kidneys. Diuretic renography with 99 mTc-ethylene dicysteine (99 mTc-EC) was performed for each patient.

Results:

Thirty-nine patients met the inclusion criteria. After diuretic renography, 29 (74.35%) patients had shown a nonobstructive pattern, and ten (25.65%) patients had a partial (intermediate) or complete obstruction. Using receiver operating characteristic (ROC) curve, none of the classic indices of Doppler duplex (i.e., resistive index [RI], resistance index, end diastolic velocity, and peak systolic velocity) had the ability to make a difference between obstructive and nonobstructive hydronephrosis. However, by calculating the difference (delta) of these indices between two kidneys of each patient, delta RI could differentiate the nonobstructive condition, significantly (P = 0.006). A cutoff value of 0.055 has 60% sensitivity and 82.8% specificity. The area under the ROC curve for delta RI is 0.795 (standard error: 0.086, 95% confidence interval [CI]: 0.626, 0.964). Furthermore, RI ratio between two kidneys of each patient could differentiate the nonobstructive condition, significantly (P = 0.012). A cutoff point of 1.075 has 70% sensitivity and 82.8% specificity. The area under the ROC curve for RI ratio was 0.769 (standard error: 0.104, 95% CI: 0.565, 0.973).

Conclusion:

This study shows that RI ratio and delta RI with a high specificity could differentiate nonobstructive hydronephrosis and therefore it is a promising way to use especially in the follow-up of children with hydronephrosis.

How can we predict ureteral obstruction after gynecological surgery? The changes in Doppler resistive index and plasma creatinine and magnesium concentrations after surgical, unilateral ureteral obstruction in a rabbit model

The aim of this study is to evaluate the changes in Doppler resistive index (RI) and plasma creatinine and magnesium concentrations after unilateral ureteral obstruction in a rabbit model. Fourteen adult female rabbits were used in this study. In seven rabbits, the left ureter was ligated with silk suture, and the control group was sham operated. Before surgery and on the second and seventh days after surgery, blood samples were obtained to measure plasma creatinine and magnesium concentrations. Doppler RIs of both kidneys were also measured before surgery and on the second and seventh days after the surgical procedure. With regard to magnesium levels, there was a significant within-subjects sessions difference [F(2, 20) = 15.21, P= 0.001] indicating a decrease through sessions. Magnesium concentrations decreased significantly at the postoperative second and seventh days compared to preoperative baseline levels (P= 0.003 and P= 0.001, respectively). Multifactorial analysis of variance was applied for each session separately with laterality, and groups as factors. The Doppler RI and the creatinine level did not show any significant differences or interactions for all sessions (P > 0.05). The decreasing plasma magnesium concentration after surgery may indicate ureteral injury; however, Doppler studies and creatinine levels may not be useful as well.

Color Doppler sonography examination of partially obstructed kidneys associated with ureteropelvic junction stone before and after percutaneous nephrolithotripsy: Preliminary report

AIM

To evaluate resistive index (RI) changes before and after unilateral percutaneous nephrolithotripsy in chronic partially obstructed kidneys due to ureteropelvic junction (UPJ) stones.

METHODS

Intrarenal RI of obstructed and contralateral normal kidneys of 18 patients were recorded immediately before the operations and at postoperative days 1, 7 and 30. Postoperative RI measurements were compared with baseline values for all patients without grouping and separately for different groups according to the preoperative RI value of the obstructed kidney.

RESULTS

Mean age and symptom duration were 27.5 years and 43.8 weeks, respectively. Preoperatively and at all postoperative controls, kidney diameters and renal parenchyma thicknesses were normal in all patients. Mean RI of obstructed kidneys decreased from 0.68 to 0.63 for all patients (P=0.032), from 0.64 to 0.63 for those with preoperative RI<0.70 (P=0.850) and from 0.73 to 0.62 for those with preoperative RI>or=0.70 (P=0.001). In patients with preoperative RI>or=0.70 in obstructed kidney, significant RI decreases were recorded at postoperative day 7 and RI differences between obstructed and contralateral kidneys disappeared after then. No difference was present pre- and postoperatively between the mean RI of obstructed and contralateral kidneys of the patients with RI<0.70. Mean RI of contralateral kidneys were normal preoperatively and showed no significant change postoperatively.

CONCLUSIONS

Preoperative RI levels may indirectly reflect the presence of functionally significant obstruction in chronic obstructed kidneys related to UPJ stones. Patients with RI>or=0.70 may have a good indication for a surgical approach. Normalization of high RI occurs rapidly after percutaneous nephrolithotripsy.

Renal Doppler Ultrasound Examination of Ureteral Obstruction in Rabbits:

RATIONALE AND OBJECTIVES

We sought to investigate the usefulness of Doppler resistive index (RI) in the diagnosis and follow-up of obstructive uropathy of different degrees and different sites of obstruction.

METHODS

Forty-six rabbits were classified as follows: group I, partial unilateral obstruction of the proximal ureter (n = 16); group II, complete unilateral obstruction of the proximal ureter (n = 17); group III, complete unilateral obstruction of the distal ureter (n = 13). The RI of the obstructed and contralateral kidneys was measured preoperatively and postoperatively 1 hour, 6 hours, 1 day, 3 days, 1 week, 2 weeks, and 4 weeks, respectively. In each group, the RI was analyzed for statistical differences in the preoperative versus postoperative kidneys, and the obstructed versus contralateral kidneys. We also analyzed the statistical differences in RIs of the obstructed kidneys, in interrenal RI differences (DeltaRI: RI of the obstructed kidney - RI of the contralateral kidney), and in RI ratio (RI of the obstructed kidney / RI of the contralateral kidney) between the 3 groups.

RESULTS

The RIs in the obstructed versus contralateral kidneys were significantly increased (P < 0.05) postoperatively at 1 hour, 1 day, and 2 weeks in group I; 6 hours and 1 week in group II; and 1 hour, 6 hours, and 3 days in group III. In obstructed kidneys, the RIs in the postoperative versus preoperative kidneys were significantly increased (P < 0.05) from 1 hour to 2 weeks in group I and from 1 hour to 4 weeks in group II. There were no statistically significant differences in mean RI, DeltaRI, and RI ratio between the 3 groups during the preoperative and postoperative period.

CONCLUSIONS

Doppler RI can be elevated in hydronephrotic kidney as a result of both partial and complete obstruction of the ureter. There are no RI differences among obstructed kidneys with different degree and different site of ureteral obstruction.

Resistive index: an experimental study of acute complete unilateral ureteral obstruction

RATIONALE AND OBJECTIVES

To study the effects of acute complete unilateral ureteral obstruction (UUO) and release on porcine renal resistive index (RI).

METHODS

Under general anesthesia, UUO was induced in six pigs. RI was measured bilaterally at predetermined intervals for 4 hours of UUO and 1 hour of release. Additionally, measures of renal blood flow (RBF), glomerular filtration rate (GFR), arterial blood pressure, renal vascular resistance (RVR), and ipsilateral renal intrapelvic pressure (IPP) were obtained.

RESULTS

UUO and resultant progressive IPP increase caused prompt and significant ipsilateral RI elevation, and contralateral RI decrease. Concomitantly, ipsilateral RVR increased significantly while RBF and GFR declined, both significantly. Release of obstruction saw an almost immediate normalization of ipsilateral RI, RVR and RBF while ipsilateral GFR assumed 80% of baseline value 15 minutes postobstruction. Throughout the experiment, ipsilateral RI correlated significantly with changes in IPP, GFR, RBF, and RVR with correlation coefficients of 0.844, -0.851, -0.898, and 0.836 respectively ( < 0.001).

CONCLUSIONS

UUO causes a divergent RI response that is instantly reversed upon release. IPP seems to be the principal effector of these changes in the early phases of UUO.

Antenatally detected, unilateral dilatation of the renal pelvis: a critical review. 2. postnatal non-operative treatment--long-term hazards, urgent research

BACKGROUND

Even after two decades, there is still much discussion about the postnatal treatment of antenatally detected, isolated pelvic dilatation (consistent with pyelo-ureteral junction obstruction). A recent review concluded that non-operative expectancy seemed safe - even after 17 years in certain cases. However, the final outcome, i.e. when these children have reached old age, is remote.

OBJECTIVE

This review takes stock of conceivable long-term hazards and evaluates prognosticating tools, and offers a basis for protocols for future randomized controlled trials. Long-term hazards: Symptoms in this context are generally considered ominous. In the antenatally detected cases, i.e. primarily asymptomatic, symptoms have been reported but they were not necessarily combined with renal damage. Hydronephroses, so mild, that they are written off, may deteriorate later on (indeed insidiously), although probably seldom. Urgent research: A predictor of outcome is eagerly pursued but hard to obtain, due to the difficulty in defining true obstruction in compliant systems such as the urinary one. Ordinary diagnostics offer no help, but there are promising innovations: constant pressure/flow assessment (flow necessary to keep a preset intrapelvic pressure), NAG/creatinine in pelvic urine, and TGFbeta-1 in voided urine. Renal microstructure, sometimes severely damaged early (which disagrees with the good results with expectancies) could possibly herald future deterioration.

CONCLUSION

Adverse developments should be meticulously documented and published swiftly, so policy can be changed if necessary, before it is too late. Cognizance of their existence, not necessarily frequency and statistics, is then first order. Efforts to design prognosticating tools has also high priority.

Resistive index in rabbits with experimentally induced hydronephrosis: effect of furosemide

RATIONALE AND OBJECTIVES

The purpose of this study in rabbits was to evaluate the effect of furosemide on resistive index (RI) in the diagnosis of partial hydronephrosis.

MATERIALS AND METHODS

In 14 rabbits the left ureter was ligated by being tied to an angiographic guide wire. Doppler sonography was performed before and 1 and 6 hours, 1 and 3 days, and 1, 2, and 4 weeks after ureteral ligation. At each interval it was performed both before and after intravenous injection of saline and furosemide. RIs were compared (a) between obstructed and contralateral kidneys and (b) before and after furosemide administration, and the statistical significance of any differences was determined.

RESULTS

Obstructed kidneys had significantly higher RIs than the contralateral kidneys before furosemide administration at five of seven postligation measurements and after furosemide administration at all seven. The differences between obstructed and contralateral kidneys were significantly higher after furosemide administration (P < .05). The increase in RI after furosemide administration was significantly greater in obstructed than in contralateral kidneys (P < .05).

CONCLUSION

The results in a rabbit model indicate that Doppler sonography with furosemide administration is a valuable method for evaluating hydronephrosis. The administration of furosemide accentuates the difference in RI between obstructed and nonobstructed kidneys.

Ultrasound contrast harmonic imaging of abdominal organs

Ultrasound contrast agents consist of microbubbles, which are the most effective acoustic backscatters. The interaction between the insonating ultrasound beam and the microbubbles is very complex and basic understanding of their behavior under various sound fields has been fundamental to the development of improved methods of visualizing and displaying the contrast agents. Although echo enhancers have been under development for a long time, their clinical applications have been limited to enhancing the Doppler signals in difficult cases. However, recent advances in harmonic imaging and the development of new tissue-specific contrast agents stand to broaden the scope of ultrasound diagnostic potential beyond simply rescuing failed Doppler examinations. This article reviews the current and potential applications of ultrasound contrast harmonic imaging in the abdomen.

Correlation between renal vascular resistance, pulse pressure, and the resistive index in isolated perfused rabbit kidneys

PURPOSE

To assess the effect of acute changes in renal vascular resistance (RVR) and pulse pressure on the resistive index (RI) measured by using Doppler ultrasonography (US).

MATERIALS AND METHODS

Rabbit kidneys were perfused by using a pulsatile perfusion system in which RVR, systolic and diastolic pulse pressures, and pulse kinetics were controlled and monitored while simultaneously measuring the RI.

RESULTS

When RVR was increased fivefold with phenylephrine hydrochloride, the RI increased only slightly (from 0.45 at baseline up to 0.50). There was a virtually linear relationship between the RI and the pulse pressure index ([systolic pressure-diastolic pressure]/systolic pressure) in the range of 0.30-0.80. The RI was not affected by the pulse rate or fraction of time that systolic pressure was applied during the pulse cycle.

CONCLUSION

Contrary to conventional teaching, which is based on theoretic considerations, the RI is not readily affected by acute changes in RVR. This indicates a need to reconsider the conventional explanations used to explain increases in RI that are frequently found in patients with renal disease or ureteral obstruction.

Renal blood flow in pigs: changes depicted with contrast-enhanced harmonic US imaging during acute urinary obstruction

PURPOSE

To evaluate contrast agent-enhanced harmonic ultrasonographic (US) imaging and Doppler hemodynamics during acute urinary obstruction.

MATERIALS AND METHODS

In 12 piglets, the distal ureter was obstructed for 60 minutes, followed by intravenous injection of furosemide. In six piglets, ureteral pressure was further elevated to mean arterial pressure, and in six other piglets ureteral obstruction was released. Contrast-enhanced harmonic imaging was performed, and interlobar resistive index (RI) and renal blood flow were determined at baseline and during each experimental condition. A bolus injection curve was constructed by plotting mean pixel intensity versus time, and the area under this normalized curve was compared with renal blood flow values.

RESULTS

Ureteral obstruction and high ureteral pressure reduced cortical renal blood flow to 88% and 66%, respectively, of baseline values. Administration of contrast agent resulted in marked homogeneous enhancement of the renal cortex. The area under the curve diminished during ureteral obstruction and correlated well with mean cortical blood flow. RI correlated well with renal perfusion pressure but poorly with changes in renal blood flow.

CONCLUSION

Contrast-enhanced harmonic US imaging depicts changes in renal blood flow during acute obstruction. Interlobar RI is a good predictor of renal perfusion pressure but not of changes in renal blood flow.

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.

Evaluation of renal resistive index, maximum velocity, and mean arterial flow velocity in a hydronephrotic partially obstructed pig model

RATIONALE AND OBJECTIVES

The authors investigate, in a controlled pig model, the usefulness of Doppler sonographic measurements of resistive index (RI), maximum velocity (Vmax), and mean velocity (Vmean) in diagnostic evaluation of the partially obstructed kidney.

METHODS

Seven female pigs underwent surgical partial unilateral renal obstruction at the ureteropelvic junction. Doppler parameters of RI, Vmax, and Vmean were measured preoperatively and postoperatively in obstructed and contralateral nonobstructed kidneys. The General Linear Model multivariate analysis of variance was used for statistical analysis of data.

RESULTS

There was no significant difference in the preoperative control values of RI (P = 0.71), Vmax (P = 0.27), and Vmean (P = 0.12). There was a statistically significant decrease in the Vmax and Vmean after postoperative day 5 in the obstructed kidney compared with the contralateral nonobstructed kidney (P = 0.01 and 0.03, respectively). There was no statistically significant difference in RI during the study.

CONCLUSIONS

In this study, RI was not a reliable indicator of partial renal obstruction. Measurements of maximal and mean blood flow velocities reached discriminatory significance only after the fifth postobstructive day, proving insensitive in the immediate postobstructive period. Vmax and Vmean demonstrated a decrease in the partially obstructed renal collecting system after 5 days of obstruction and may serve as useful parameters in the evaluation of obstruction after the immediate acute period, when compared with a nonobstructed contralateral system.