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.     

Intrarenal Doppler ultrasound studies in normal and acutely obstructed kidneys.

Renal ultrasound examinations and intrarenal arterial Doppler studies were performed on 48 patients with normal renal tracts and 20 patients presenting with acute renal colic resulting from ureteric calculus, 14 of whom had urographic evidence of renal obstruction. The mean resistance index (RI) of the Doppler waveforms obtained on the 14 obstructed kidneys (70.4 +/- 6.22) was significantly higher than the mean RI of the 96 normal kidneys (62.4 +/- 6.43). The mean difference between the RIs of the obstructed kidneys and their contralateral non-obstructed kidneys (8.37 +/- 4.43) was also significantly higher than the differences in RI seen between pairs of normal kidneys (2.70 +/- 1.71). Five out of 14 obstructed kidneys showed no pelvicalyceal dilatation and could not have been shown to be obstructed on conventional sonography. Four of these five had RI changes suggestive of obstruction and thus 13 of 14 obstructed kidneys would have been identified as obstructed by a combination of Doppler and conventional sonographic findings. 10 of the 14 obstructed kidneys were re-examined after passage of a urinary calculus and nine showed a reduction in the RI of the previously obstructed kidneys. The 10th subsequently required ureterolithotomy.     

Quantitative SPECT of 99mTc-DMSA uptake in kidneys of infants with unilateral ureteropelvic junction obstruction: assessment of structural and functional abnormalities.

We evaluated individual renal function using quantitative SPECT of dimercaptosuccinic acid (DMSA) uptake by the kidneys (QDMSA) in infants with unilateral ureteropelvic junction (UPJ) obstruction and compared our findings with infants without obstruction. METHODS: QDMSA was performed on 13 infants (mean age of 2.8 +/- 2.8 mo) with unilateral UPJ obstruction and on 15 age-matched controls without obstruction. RESULTS: Control kidneys (n = 30) had a volume of 43.5 +/- 8.8 mL, a percentage injected dose (%ID)/mL 0.62 +/- 0.12 and uptake of 26.1% +/- 3.9%. Kidneys with UPJ obstruction (n = 13) had a volume of 61.2 +/- 19.3 mL, a %ID/mL of 0.42 +/- 0.11 and uptake of 25.4% +/- 8.2%. Contralateral kidneys (n = 13) had a volume of 44.0 +/- 11.9 mL, a %ID/mL of 0.57 +/- 0.16 and uptake of 24.2% +/- 4.6%. The uptake in obstructed kidneys was similar to that observed in contralateral and control kidneys (t = -0.77, P = 0.45; t = -0.37, P = 0.71; respectively). UPJ kidneys had a statistically significant increased volume and decreased %ID/mL, compared with contralateral kidneys (t = 3.35, P < 0.006 and t = 3.75, P < 0.003, respectively) and control kidneys (t = -4.2, P < 0.001 and t = 4.7, P < 0.001, respectively). There was no significant difference between contralateral kidneys and control kidneys regarding volume (t = -0.16, P = 0.87), %ID/mL (t = 0.98, P = 0.33) and uptake (t = -1.41, P = 0.16). Of 13 infants, 11 (85%) showed large kidneys with thinning of the renal cortex. In 1 infant, there was no difference between the obstructed and contralateral kidneys regarding volume, %ID/mL and uptake, and 1 infant showed significant decreased uptake in the UPJ kidney compared with the contralateral kidney. CONCLUSION: Although the overall renal function of the obstructed kidneys remained unchanged, there was a statistically significant decrease in the %ID/mL of renal tissue in UPJ kidneys, which may represent renal dysfunction. Increased functional volume with a thin cortex may represent a compensatory mechanism of the obstructed kidney. Such changes may contribute to the understanding of pathophysiologic mechanisms and may be an early sign of obstruction in infants with hydronephrosis. Further longitudinal studies with an extended number of infants and serial measurements of kidney volumes and %ID/mL are warranted to assess the significance of QDMSA in the management of infants with asymptomatic unilateral renal pelvic dilatation.     

Radiological investigation for expert and medico-legal purposes

PURPOSE: To investigate whether colour Doppler US can demonstrate haemodynamic differences in patients with renal colic after pharmacological treatment with indomethacin and ketorolac. MATERIALS AND METHODS: We studied 180 consecutive patients with unilateral acute renal colic with colour Doppler US; 90 were treated with indomethacin, 90 with ketorolac. Furthermore, 37 consecutive patients without obstruction (17 treated with indomethacin and 20 with ketorolac) were also examined and considered normal controls. RESULTS: In the patients with renal colic the average resistive index (RI) was significantly greater on the side of the colic after administration of either indomethacin or ketorolac (p<0.001). The average RI in the obstructed kidneys was significantly higher in the patients treated with ketorolac than with indomethacin (p<0.005). No statistically significant differences were shown between the average RIs of the non obstructed kidneys of the patients with renal colic and between the kidneys of the control patients treated with either indomethacin or ketorolac. DISCUSSION AND CONCLUSIONS: Doppler evaluation of patients with renal colic requires careful interpretation after the administration of nonsteroidal anti-inflammatory drugs (NSAIDs), since values of renal RI depend on the drug that has been used to relieve symptoms.     

Unenhanced urinary CT: value of parenchymal attenuation measurements in differentiating acute vs. chronic renal obstruction

Objective

We aimed to search if the renal parenchymal attenuation measurements on unenhanced CT scans could be useful in differentiating acutely obstructed kidneys from chronic cases or unobstructed kidneys.

Material and methods

Unenhanced CT scans of 101 patients were retrospectively reviewed. Thirty-two patients with unilateral acute renal obstruction, 34 patients with unilateral chronic renal obstruction due to various reasons and 35 control subjects were included in the study. The parenchymal densities of both kidneys were measured, from the upper poles, middle portions, and lower poles of each kidney. The mean parenchymal densities of both kidneys were calculated in all three groups of subjects. Secondary signs of renal obstruction such as perinephric stranding, size of ureteral stone, degree of hydronephrosis were also noted for each kidney.

Results

The mean parenchymal attenuation value on the acutely obstructed side was lower than the unobstructed side, 24.21 ± 3.68 and 30.68 ± 4.75 respectively (p < 0.001). The mean parenchymal attenuation value on the acutely obstructed side (24.21 ± 3.68) was lower than both the chronically obstructed side (30.85 ± 4.53), and the control subjects (29.62 ± 3.03 on corresponding side). There was no statistically significant attenuation difference between right and left kidneys in the control group and chronic obstruction group.

Conclusion

Renal parenchymal attenuation measurements and attenuation differences of both kidney of same patient could be useful in differentiating acute unilateral obstruction from chronic cases.     

MSCT灌注成像对积水肾脏单肾功能评价的实验研究

目的采用多层螺旋CT（MSCT）灌注成像技术测定肾积水模型的各项灌注参数,探讨其对积水肾脏单肾功能的诊断价值。材料与方法8周龄以上成年健康雄性实验大白兔20只,制作右侧输尿管部分梗阻模型．分别在梗阻前、梗阻后4周行MSCT灌注扫描、单光子正电子发射计算机体层成像（SPECT）检查及彩色多普勒超声显像（CDFI）检测,取积水肾脏标本,光镜下观察病理学变化。结果梗阻后4周MSCT灌注成像可见肾盂扩张,肾皮质明显变薄,皮、髓质血流量（BF）、血容量（BV）较梗阻前有明显下降（P〈0．01）,对比剂平均通过时间（MTT）变化无明显差异,肾皮质表面通透性（PS）有轻度下降趋势,但与梗阻前相比,无显著性差异,而肾髓质PS则较梗阻前有显著性降低（P〈0．01）。CDFI显示梗阻后肾动脉、肾内动脉收缩期峰值速度（PSV）均降低（P〈0．05）,舒张末速度（EDV）显著低于梗阻前（P〈0．01）,阻力指数（RI）显著高于梗阻前（P〈0．01）。SPECT测定结果显示梗阻后右肾肾小球滤过率（GFR）均显著低于梗阻前（P〈0．001）,达峰时间（Tb）显著延长（P〈0．001）,半排时间（T（1/2））显著延长,无测定意义。结论肾积水模型在梗阻前、后皮、髓质MSCT灌注参数的变化以BF、BV下降最明显。此结果与CDFI测定的PSV、EDV及RI所反映的肾血流动力学变化相一致。MSCT灌注技术的出现无疑为l临床评价单肾功能开拓了思路,随着MSCT灌注软件的不断发展,其在单肾功能评价方面一定会显示出巨大的临床应用价值。     

Distinction between obstructive and nonobstructive pyelocaliectasis with duplex Doppler sonography

Because animal studies have shown that renal obstruction increases renal vascular resistance, we theorized that obstruction would change the Doppler waveform. We studied the value of the resistive index (RI) calculated from the duplex Doppler waveform to distinguish between obstructive and nonobstructive pyelocaliectasis in 229 kidneys in 133 patients. The RI is the peak systolic frequency shift minus the minimum diastolic frequency shift, then divided by the peak systolic frequency shift. Duplex Doppler sonography was performed prospectively in 70 kidneys with pyelocaliectasis before the presence or absence of obstruction was established. In 54 of 70 kidneys, the presence or absence of obstruction was proved by interventional methods (percutaneous nephrostomy, antegrade or retrograde pyelography, loopography), and in the rest it was proved by body CT, excretory urography, or surgery. Thirty-eight kidneys were found to be obstructed, and 32 had nonobstructive dilatation. In addition, 159 kidneys without pyelocaliectasis were studied to identify possible limitations of Doppler sonography in the diagnosis of obstruction. Clinical history and laboratory data were used to determine that 109 of these kidneys were in normal subjects and 50 were in patients with nondilated renal disease. There was a significant difference between the mean RI of the obstructed (0.77 +/- 0.05) and the nonobstructed dilated (0.63 +/- 0.06) kidneys (p less than .01). Analysis of the receiver-operating-characteristic curve showed an RI of 0.70 to be a good discriminatory level for obstruction, resulting in a sensitivity of 92%, a specificity of 88%, and an accuracy of 90%. All 109 normal kidneys had an RI less than 0.70. Over half (27/50) of the kidneys in patients with nondilated renal disease had an elevated RI (greater than or equal to 0.70). Ninety-six patients had Doppler examinations on both kidneys, and in only six patients did the RI values of each kidney differ by more than 0.10; all six were proved to have unilateral obstruction. Use of duplex Doppler sonography should improve the specificity, and thus the accuracy, of sonography in the noninvasive diagnosis of obstruction and should be used when a dilated collecting system is identified.     

Pre- and postnatal diagnostic imaging of congenital urinary tract disorders

The prenatal diagnosis of urinary tract obstruction was made in 10 neonates. These findings were confirmed postnatally by sonography, urography, voiding cystourethrography, and scintigraphy. There were 8 neonates with unilateral obstruction of the ureter, and 2 with urethral valves and reflux. Nephrectomy because of hydronephrosis was necessary in 2 instances. The prenatal diagnosis of a urinary tract obstruction is of great importance, because the neonate may be operated upon without delay. Thus the diseased kidney can be saved. Diuretic radionuclide urography is helpful in differentiating between dilated obstructed and dilated nonobstructed kidneys.     

Doppler-duplex ultrasound in renal colic

Objective: To determine the role of intrarenal Doppler ultrasound (US) in patients with renal colic and to establish the usefulness of this diagnostic method. Materials and methods: In 121 patients with renal colic and 70 healthy individuals, 382 kidneys were examined with color duplex US. Mean intrarenal-arterial resistive index (RI), and the difference of mean RIs (dRI) between both kidneys were determined. In 64 patients, RI and dRI were compared with urographic findings (time of delay pyelogram between both kidneys). Results: In the 70 healthy individuals, RI was 0.62 ± 0.045 and dRI 0.018 ± 0.01. In the 121 patients with renal colic, RI (0.71 ± 0.06) was significantly superior (P < 0.001) with respect to the opposite kidney, with a dRI of 0.09 ± 0.055. In a correlation performed in 64 patients with urographic findings among color doppler US, with a RI ≥ 0.70 and/or dRI ≥ 0.06 as an indicative value of obstruction, sensitivity and specifity were 91.8% for patients with delayed pyelogram (n = 37 patients), and 48.1% for patients with nondelayed pyelogram (n = 27 patients) with a specificity of 92.8% with respect to the group of normal patients. In the group of patients with delayed pyelogram, RI was significantly superior (P < 0.05) in patients with an evolution time greater than 24 hours, in patients with proximal ureteral obstruction and in patients who had signs of pyelonephritis. There were no significant differences in the group of patients with nondelayed pyelograms. Conclusion: Color Doppler US is useful to fundamentally evaluate the consequences of the obstruction on renal function. Other factors such as evolution time of the symptomology, obstruction level, or existence of pyelonephritis can alter the US-Doppler values.     

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.     

Renal elasticity and perfusion changes associated with fibrosis on ultrasonography in a rabbit model of obstructive uropathy

To evaluate elasticity and perfusion change associated with fibrosis in a rabbit model of unilateral ureter obstruction using shear wave elastography (SWE) and contrast-enhanced ultrasonography (CEUS). Complete unilateral ureter obstruction by ligation was performed in the left kidney of 15 rabbits. Renal elasticity on SWE and perfusion change on CEUS at the renal cortex were measured before and after the operation. Histopathological renal fibrosis was quantified by the stained area ratio with Masson trichrome and Picrosirius red using ImageJ analysis. Renal elasticity and perfusion values were compared by the Mann-Whitney U test and Proc Mixed as a function of time. Spearman’s correlation was used to analyze differences between imaging values and fibrosis. The duration of imaging follow-up was up to 49 days, with interval imaging performed 1–3 times. Renal elasticity values were higher in obstructed kidneys compared to contralateral kidneys (31.0 kPa vs 16.4 kPa, p < 0.001) and increased according to postoperative time (0.46 kPa/day). With respect to renal fibrosis, SWE values were positively correlated with Masson trichrome (ρ = 0.651, p < 0.001) and Picrosirius red (ρ = 0.514, p = 0.007). Among CEUS parameters, mean transit time was negatively correlated with renal fibrosis by Masson trichrome (ρ = − 0.639, p = 0.001) and Picrosirius red (ρ = − 0.625, p = 0.001). Rise time and time to peak were positively correlated with renal fibrosis. Obstructive uropathy resulted in changes to both renal elasticity and perfusion. Renal fibrosis was moderately associated with increased renal cortical stiffness and both delayed and decreased cortical perfusion. • Obstructive uropathy causes changes in elasticity and perfusion in a rabbit model. • Renal fibrosis from obstructive uropathy increases renal cortical stiffness, and both delay and decrease cortical perfusion.     

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.     

MSCT灌注成像评价单侧输尿管完全梗阻后肾损伤的实验研究

目的探讨64排MSCT灌注成像在单侧输尿管完全梗阻后对动物肾脏损伤程度的评估价值。方法将25只雄性新西兰大白兔制成左侧输尿管完全梗阻模型,分别测量梗阻前及左侧输尿管完全梗阻术后1、3、5及7周梗阻侧肾脏64排MSCT各灌注指标,用核素测定其肾小球滤过率,各阶段分别处死1只获取肾脏标本。结果梗阻后1、3、5及7周MSCT灌注成像之肾皮质血流量（BF）、血容量（BV）逐渐降低,对比剂达峰时间（TTP）明显滞后。核素测定显示梗阻后左肾肾小球滤过率（GFR）较梗阻前逐渐降低。结论MSCT灌注成像对积水肾肾功能损伤程度的评估有一定价值,且与核素检查基本吻合。     

MSCT灌注成像与SPECT对积水肾脏单肾功能评价的实验对比研究

目的探讨MSCT灌注成像对积水肾脏单肾功能的诊断价值方法8周龄以上成年健康雄性实验大白兔20只,制作右侧输尿管部分梗阻模型,分别在梗阻前、梗阻后4周行MSCT灌注扫描、单光子正电子发射计算机体层成像(SPECT)检查结果梗阻后4周MSCT灌注成像可见肾盂扩张,肾皮质明显变薄,皮、髓质血流量(BF)和血容量(BV)较梗阻前有明显下降(P<0.01),对比剂平均通过时间变化无统计学意义,肾皮质表面通透性(PS)有轻度下降趋势,但与梗阻前相比,无统计学意义,而肾髓质PS则较梗阻前有显著性降低(P<0.01)SPECT测定结果显示梗阻后右肾肾小球滤过率(GFR)均显著低于梗阻前(P<0.001),Tb显著延长(P<0.001),T1/2显著延长,无测定意义结论MSCT灌注技术对评价积水肾脏单肾功能具有一定的临床应用价值     

Renal obstruction in patients with ileal loops: US evaluation

Ultrasound (US) is often employed as a screening test for hydronephrosis in the nondiverted kidney and has been used recently to evaluate the diverted kidney, specifically ileal loops, for obstruction. The utility of US in evaluating obstruction in patients with ileal loops has apparently not been previously explored. During a 2-year period, 87 kidneys drained by an ileal loop diversion were examined with US because of clinical indications of possible renal obstruction. In 33 kidneys, no hydronephrosis was seen on sonograms, and no obstruction was later proved; in 51 kidneys, shown by US to be hydronephrotic, only 19 (37%) were obstructed. Three left kidneys were not visualized with US. The percentage of hydronephrotic kidneys subsequently shown to be obstructed increased rapidly as the US appearance progressed from grade 1 (20%) to grade 3 (80%). In this series, US had a 100% sensitivity and a 50% specificity in evaluating patients with ileal loops for renal obstruction. Thus, for the adult patient, a direct contrast evaluation of the collecting system is suggested; for the pediatric patient, initial use of US is justified as a means to avoid radiation exposure.     

Duplex Doppler US of the kidney: differentiation of obstructive from nonobstructive dilatation

Distinction of the obstructed from the nonobstructed dilated renal collecting system is a difficult problem often requiring interventional procedures and pressure measurements. The authors prospectively performed duplex Doppler ultrasound (US) evaluations in 21 kidneys (obstructed, n = 14; nonobstructed, n = 7) immediately before percutaneous nephrostomy. In addition, ten of the obstructed kidneys were evaluated with follow-up Doppler US after percutaneous nephrostomy. Renal obstruction caused a change in the Doppler waveform detected by means of the resistive index (RI). Thirteen of the 14 obstructed kidneys had a RI value greater than .70, while none of the nonobstructed kidneys had a RI value exceeding .70. Relief of the obstruction resulted in a reduced RI; in nine of ten kidneys, the RI was less than or equal to .70 (similar to that of the nonobstructed kidneys). When a dilated collecting system is being imaged, additional evaluation with duplex Doppler US may help distinguish obstructed from nonobstructed dilatation, which may be of particular benefit in patients with conditions that usually predispose them to collecting system dilatation.     

经皮肾镜手术前后肾阻力指数变化在肾功能中的应用评价

目的：应用经皮肾镜手术前后肾阻力指数（RI）的变化来评价肾功能。方法采用随机、平行对照的临床研究方法,对纳入本研究的40例患者,记录经皮肾镜手术前、手术后0.5 h、手术后2周时双侧肾上、中、下段肾叶间动脉阻力指数,以及血液肌酐、尿素氮数据,分析肾动脉阻力指数与肾功能变化的关系。结果①患侧肾在经皮肾镜术前2 h与术后0.5 h叶间动脉RI值相比较,差异有统计学意义（t=2.72,P＜0.05）,术后1周的叶间动脉RI值相比较,差异有统计学意义（t=3.57,P＜0.05）,而健侧肾在经皮肾镜术前与术后0.5 h叶间动脉RI值相比,差异无统计学意义（t=1.63,P＞0.05）,而与术后2周叶间动脉RI值相比,差异有统计学意义（t=3.31,P＜0.05）;②患者的术前2 h血液中肌酐与术后0.5 h相比,差异无统计学意义（t=1.33,P＞0.05）,而与术后1周相比,差异有统计学意义（t=3.86,P＜0.05）,患者的术前2 h血液中尿素氮与术后0.5 h相比,差异无统计学意义（t=2.01,P＞0.05）,而与术后1周相比,差异有统计学意义（t=3.57,P＜0.05）;③患者健侧肾术前、术后RI值与肌酐、尿素氮变化无相关性,而患侧肾术前、术后RI值与肌酐、尿素氮的变化呈负相关（r=-0.37,P＜0.05）。结论可以应用经皮肾镜手术前后肾RI的变化来评价肾功能的变化,为泌尿科微创取石手术提供临床依据。     

Renal diuretic duplex Doppler sonography in childhood hydronephrosis

OBJECTIVE: The purpose of this study was to determine the diagnostic value of diuretic duplex Doppler sonography in distinguishing between obstructive and nonobstructive hydronephrosis in children by calculating the resistive indices (RI) before and after administration of furosemide. MATERIAL AND METHODS: We prospectively evaluated 28 kidneys (2 solitary) in 15 patients with unilateral or bilateral neonatal hydronephrosis. All patients underwent diuretic renography and duplex Doppler sonography before and after administration of furosemide. RESULTS: According to the half-time drainage patterns at diuretic renography, 13 kidneys were classified as nonobstructed and 15 as obstructed. At baseline, the mean RI values of nonobstructed and obstructed kidneys were not significantly different (0.66 and 0.64, respectively). Ten minutes after the injection of furosemide, the mean RI values of the nonobstructed and obstructed kidneys were 0.68 and 0.70, respectively. The increase in RI over the baseline 10 min after the diuretic injection was statistically significant (p<0.00001) in the obstructed kidneys. CONCLUSION: The baseline RI value of 0.70 is not a definite value for distinguishing obstructed from nonobstructed systems. An increase in RI of at least 10% over the baseline seems to be a more reliable criterion, especially when it is used in conjunction with diuretic renography.     

Renal transplant pyelocaliectasis: role of duplex Doppler US in evaluation

To distinguish the obstructed from the nonobstructed dilated collecting system of transplanted kidneys without interventional diagnostic measures, the authors prospectively evaluated duplex Doppler analysis (determination of resistive index [RI]) in 35 renal transplant patients with pyelocaliectasis. Proof of the presence or absence of obstruction was obtained at interventional procedures in 18 patients and at clinical follow-up in 17. Thirteen kidneys were obstructed (mean RI, .81 +/- .06), while 22 had nonobstructive dilatation (mean RI, .66 +/- .07). The RI difference was statistically significant (P less than or equal to .01). Of 21 kidneys with a normal RI, only two had obstruction. In both of these, the obstruction was associated with a significant peritransplant collection of fluid due to a ureteral leak. In the seven obstructed transplanted kidneys with follow-up, the mean RI was .82 +/- .06 before nephrostomy and .67 +/- .05 after nephrostomy. Obstruction was a common cause of an elevated RI (greater than or equal to .75). Other causes of transplant dysfunction can be associated with an elevated RI and nonobstructed dilatation. More important, a normal RI should strongly argue against obstruction unless a ureteral leak is also present.     

The absent kidney in 99Tcm-MAG3 renogram: a dramatic reversible consequence of contrast nephrotoxicity superimposed on renal obstruction

99Tcm-mercaptoacetyltriglycine (MAG3) renogram is a robust imaging technique used to delineate upper urinary tract obstruction. The changes observed on the renogram are often reversible on relief of obstruction. We present two cases illustrating the extreme consequence of contrast nephrotoxicity on pre-existing obstructed kidneys. In one case, this led to severe impairment of perfusion and uptake observed on 99Tcm-MAG3 renogram and in the second case virtual non-visualization of the obstructed kidney. Subsequent treatment of obstruction, led to dramatic improvement in renal function. It is important for clinicians, nuclear medicine physicians and radiologists to be aware of the potential of contrast nephrotoxicity in obstructed kidneys.