Resistance and pulsatility indices in acute renal obstruction

Is contrast-enhanced ultrasonography (CEUS) useful in the assessment of obstructive uropathy-induced perfusion disorders?

Aim: The study aimed to evaluate the usefulness of contrast-enhanced ultrasonography in renal perfusion disorders caused by obstructive uropathy. Case description: We present a case of a patient with a horseshoe kidney, in which the urine outflow from the right part of the kidney was blocked due to the presence of a bladder tumour infiltrating the ureter. Perfusion disorders in both parts of the kidney, visible in computed tomography, were partially reflected in the ultrasound image. Conclusions: Doppler ultrasound and contrast-enhanced ultrasound may be useful for monitoring perfusion disorders in the course of obstructive uropathy, provided that appropriate methodology is developed to compare blood flow in both kidneys.

Doppler sonographic evaluation of resistive index of intra-renal arteries in acute ureteric obstruction

BACKGROUND

Acute ureteric colic is one of the most commonly encountered acute abdominal conditions. Diagnosis of obstruction caused by ureteric calculus occasionally becomes challenging if there is inadequate dilation of the urinary tract proximal to obstruction. In such a situation, intra-renal artery Doppler parameters can be used as a diagnostic tool. Our study compared intra-renal arterial Doppler in patients with obstructed and non-obstructed kidneys presenting within 24 h of onset of symptoms of unilateral acute renal colic.

RESULTS

The resistivity index (RI) in the segmental arteries of all 54 patients with obstructed kidneys was significantly higher than in those with non-obstructed kidney: 0.75 vs. 0.56, with a p value less than 0.001, a sensitivity of 85% and a specificity of 93%.

CONCLUSION

Doppler ultrasound is a useful diagnostic tool in the evaluation of acute renal obstruction, thus enabling practitioners to avoid ordering unnecessary CT and exposing patients to ionizing radiation. An RI value > 0.7 has good sensitivity and specificity in our study. The results obtained in the study were comparable to those of pioneer studies conducted worldwide.

Renal Doppler ultrasound resistive index vs. renal scintigraphy with 99mTc-DTPA as diagnostic test for ureteropelvic junction obstruction in children

OBJECTIVE

A cross-sectional study was carried out with the objective of evaluating the usefulness of Doppler ultrasound with resistive index (RI) measure compared with renal scintigraphy with ^99mTc-DTPA in children with unilateral ureteropelvic junction obstruction.

METHODS

The study included children under 15 years with a diagnosis of unilateral ureteropelvic junction obstruction, healthy contralateral kidney with or without an antecedent of ureteropyeloplasty. The selected patients were sent to the Nuclear Medicine Department to carry out a renal scintigraphy with ^99mTc-DTPA and days later were sent to the Radiology Department for the performance of Renal Doppler Ultrasound with RI.

RESULTS

A total of 21 patients were included in the study, 15 males and 6 females, representing 71.4% and 28.6%, respectively. Mean age was 5.3 years. Only 3 had an antecedent of ureteropyeloplasty in the affected kidney. The scintigraphy reported data of unilateral obstruction in 18 patients, including the 3 patients with previous surgery. The average glomerular filtration rate (GFR) obtained with the scintigraphy was 100.28ml/min. The average GFR in affected kidneys was 43.03ml/min and 57.24ml/min in healthy kidneys (p<.001). Doppler ultrasound with RI reported ectasia in 100% of the affected kidneys and one normal contralateral kidney. The average RI in affected kidneys was 0.69mm/s and 0.50mm/s in healthy kidneys (p<.001).

CONCLUSIONS

With the results obtained, we can suggest that ultrasound Doppler with measurement of RI can be an alternative tool to renal scintigraphy with ^99mTc-DTPA in some cases.

Effects of medetomidine on intra-renal arteries resistive and pulsatility indices in clinically normal adult domestic shorthair cats

The aim of this study was to determine the effects of intramuscular injection of medetomidine on intra-renal arteries resistive and pulsatility indices by duplex Doppler ultrasonography in clinically normal adult domestic shorthair cats. For this purpose, twenty-six neutered adult healthy domestic shorthair cats (13 females and 13 males) were evaluated. B-mode, color Doppler and pulsed wave Doppler ultrasonography of right and left kidneys were performed to record the resistive index (RI) and pulsatility index (PI) of intra-renal arteries. To minimize statistical errors, the mean RI and PI were determined for each kidney by averaging three waveforms from the intra-renal arteries. Twenty-four hr later, the cats were sedated by 0.04 mg kg-1 intramuscular administration of medetomidine. All the Doppler measurements were repeated 15 min after drug administration. Mean ± standard deviation )SD( of PI and RI of the intra-renal arteries before administration of intramuscular medetomidine were 1.03 ± 0.08 and 0.61 ± 0.02, respectively. Fifteen min after medetomidine administration, the mean ± SD of PI and RI values were 1.04 ± 0.08 and 0.61 ± 0.02, respectively. Significant differences were not detected in mean PI and RI values before and 15 min after drug administration. Our findings showed that intramuscular administration of medetomidine does not cause significant hemodynamic changes in the intra-renal arteries after 15 min.

Renal Venous Doppler Study in Obstructive Uropathy

INTRODUCTION

Obstructive uropathy is very common cause of pain abdomen. Recognition of the cause of the pain and level of obstruction is the goal. Ultrasound is the primary modality used for detection and characterization of obstructive uropathy along with conventional radiographs. Obstructive uropathy in early stages can be difficult to diagnose using standard B-mode USG or arterial sensitive index.

AIM

The purpose of this study is to evaluate the diagnostic accuracy of renal venous doppler ultrasound in diagnosing acute obstructive uropathy either alone or in addition to arterial doppler study of inter lobar arteries. As there is limited literature available till date on Indian population regarding renal venous doppler in obstructive uropathy, this study can be useful.

MATERIALS AND METHODS

Fifty patients presenting with features suggestive of obstructive uropathy were studied and compared with non-obstructed kidney of the same patient. Fifty normal individuals were studied and taken as controls.

RESULTS

The mean venous impedance index on the obstructed side (0.26 ± 0.07) was less than the mean venous impedance index on the unobstructed side (0.41 ± 0.08) and was statistically highly significant. There was no statistically significant difference in mean arterial Resistivity Index (RI).

CONCLUSION

Thus renal venous doppler study is a reliable tool in diagnosing cases of acute obstructive uropathy. Though its use as single parameter to identify obstruction still needs further studies, it can be used in conjugation with b mode ultrasound and arterial Doppler to identify obstruction.

Role of resistive index in renal colic

We studied the role of duplex Doppler ultrasonography in the diagnosis of renal obstruction caused by ureteral calculi. Using duplex Doppler sonography, we evaluated the intrarenal hemodynamics of 27 patients who presented to the emergency department with renal colic. We performed Doppler ultrasonography on patients in whom US did not reveal any pathology causing renal colic and calculated and compared mean RI values of normal and obstructed kidneys and DeltaRI values of each group. Threshold levels for the diagnosis of urinary tract obstruction (mean RI > or = 0.70 and DeltaRI > or = 0.08) were used to determine the sensitivity and specificity of Doppler sonography for the diagnosis of urinary tract obstruction. Patients were investigated for revealing calculi diagnosis either by stone excretion history, intravenous pyelography or non contrast enhanced urinary computed tomography. A total of 162 intrarenal arterial Doppler recordings were made on 54 kidneys. Of the 16 patients with urinary obstruction, 11 (68%) had sonographic evidence of pelvicalyceal dilatation. The mean RI of the 16 obstructed and 11 unobstructed kidneys was 0.69 +/- 0.04 and 0.61 +/- 0.06 (mean +/- standard deviation), respectively. The difference between the mean RI values for each group was statistically significant (P < 0.05). Mean RI values of the contralateral kidneys in the obstructed group and unobstructed group were 0.61 +/- 0.03 and 0.59 +/- 0.05, respectively. Also DeltaRI value (0.07 +/- 0.02) of obstructed kidney group was statistically higher than the DeltaRI value (0.01 +/- 0.03) of the unobstructed group (P < 0.05). The mean RI of the 16 obstructed kidneys (0.69 +/- 0.04) was significantly greater than that of the 16 unobstructed contralateral kidneys (0.61 +/- 0.03) (P < 0.05). This study supplements the existing evidence that, in acutely obstructed kidneys, renal Doppler recording can demonstrate altered renal perfusion before pelvicalyceal system dilatation and distinguish obstructed and unobstructed kidneys evaluated with suspicion of renal colic.

Doppler ultrasonographic changes in the canine kidney during normovolaemic anaemia

The haemodynamics of the canine left renal artery (LRA) and interlobar artery (ILA) were evaluated in eleven fasted, healthy, conscious beagles with severe acute (haematocrit [Hct] 16%), moderate chronic (Hct 26%) and mild chronic (Hct 34%) normovolaemic anaemia using Doppler ultrasound. Heart rate, peak systolic velocity (PSV), end diastolic velocity (EDV), time-averaged mean velocity (TAVmean), pulsatility index (PI) and resistive index (RI) were recorded. Doppler values in the dogs following the induction of anaemia states were compared with corresponding values in the same dogs prior to the induction of anaemia. Left renal artery mean PSV, mean PI and mean RI were significantly higher and the mean EDV was significantly lower in severe acute anaemia. No significant change was seen in mean values of the same parameters in moderate or mild chronic anaemia. There was no significant change in TAVmean of the LRA or mean PI and mean RI of the ILA in any grade of anaemia. Acute, severe normovolaemic anaemia significantly altered LRA Doppler parameters in resting dogs without influencing those of the ILA. Moderate or mild chronic anaemia had no effect on any renal Doppler parameter.

Functional evaluation of the urinary tract by color-Doppler ultrasonography (CDU) in 100 patients with renal colic

INTRODUCTION AND OBJECTIVE

To evaluate if the addition of a renal color-Doppler ultrasonography (CDU) in the setting of acute renal colic improves the sensitivity of conventional sonography.

MATERIALS AND METHODS

Between July 2002 and June 2003, 100 patients (median 49 years) with renal colic have been evaluated. Within 24 h of the admission, a CDU study of the urinary tract was performed using a sonograph GE Logiq 500 PRO with a multifrequency (3-5 MHz) convex probe. The following parameters were evaluated: ultrasonography (US) of both kidneys, ureters and bladder; resistive index (RI) of the arciform arteries of both kidneys in three different parenchymal areas; ureteric jets in response to hydration. A renal RI>0.70 and/or a 10% difference between the kidneys were considered as diagnostic of obstructive uropathy; an asymmetric and/or reduced ureteric jet from the ureteric orifices was an additional indicator of obstruction. All patients underwent a CT scan both with and without the administration of contrast medium.

RESULTS

Enhanced helical CT demonstrated an urinary stone in 90 out of the 100 patients (90%): 29 pyelic, 28 at the pyelo-ureteral junction, 23 lumbo-iliac and 10 juxtavesical stones. Among 90 patients with urolithiasis, the stone was undetectable with US in 11 cases (12.2%); in 8 cases (8.9%) pyelocalicectasis was absent, and in 6 patients (6.6%) a non-obstructive hydronephrosis was present. Median RI in obstructed and non-obstructed kidney was 0.73 (range 0.71-0.87) versus 0.62 (0.50-0.68), respectively; in two, obstructed kidneys RI was <0.70 but greater than 10% compared with normal side. Sensitivity and specificity of US, CDU (RI+ureteric jet), unenhanced helical CT and CDU in association with unenhanced helical CT were 94.8 and 55.5, 98.9 and 90.9, 100 and 100%, respectively.

DISCUSSION AND CONCLUSIONS

CDU in patients with renal colic and/or pelvicalicectasis improves the diagnostic accuracy of US in distinguishing between obstructive and non-obstructive dilatation. Combined with unenhanced CT, CDU has a 100% sensitivity and specificity. Moreover, due to the absence of contraindications and side-effects, CDU is indicated for the follow-up of patients after ESWL, pregnant women and children.

Doppler sonography of renal obstruction: value of venous impedance index measurements

OBJECTIVE

Arterial resistive index values have poor sensitivity and specificity for alterations in renal perfusion induced by collecting system obstruction. We aimed to determine whether the intrarenal venous impedance index values could be useful in evaluating renal parenchymal compliance in cases of obstruction and in differentiating acute obstruction from chronic cases.

METHODS

Fifteen patients with acute renal colic having unilateral stone disease and another 15 patients having unilateral chronic obstruction due to various causes were evaluated sonographically. The diagnosis was confirmed either by computed tomography or intravenous urography in all cases. Fifteen subjects with normal kidneys were investigated as a control group. All patients were examined prospectively by conventional and Doppler sonography. The impedance indices and peak flow signals of the interlobar arteries and veins of both kidneys were calculated from spectral Doppler waveforms in all 3 groups.

RESULTS

The mean venous impedance index on the acutely obstructed side was lower than the index on the unobstructed side: 0.25 +/- 0.07 and 0.53 +/- 0.3 (mean +/- SD), respectively (P = .005). The mean venous impedance index on the acutely obstructed side was less than the indices both on the chronically obstructed side and in the control subjects (P > .0001). In acute cases, the mean arterial resistive index on the obstructed side was higher than the index on the unobstructed side: 0.62 +/- 0.06 and 0.57 +/- 0.06, respectively (P = .001). No statistically significant difference was detected between other parameters evaluated for the test and control groups.

CONCLUSIONS

Renal venous impedance index values may be helpful in evaluating renal hemodynamics in obstruction and in differentiating acute obstruction from chronic cases when used in conjunction with the arterial resistive index.

Renal vein Doppler sonography of obstructive uropathy

OBJECTIVE

Obstructive uropathy in the early stages can be difficult to diagnose using either standard sonography or the arterial resistive index. We tested the hypothesis that acute obstruction of the renal collecting system reduces the intraparenchymal renal compliance, which affects the intraparenchymal venous blood flow to a greater degree than the arterial flow.

SUBJECTS AND METHODS

Twelve patients with clinical evidence of acute obstructive uropathy were referred for helical CT to confirm the diagnosis and to provide a gold standard by which we could evaluate the sonographic findings in the 12 test patients. Twelve patients without renal disease served as a control group. Doppler sonography of the interlobar arteries and veins of both kidneys then was performed, with the sonographer unaware of which kidney had an obstruction. Peak venous flow measurements and arterial resistive and venous impedance indexes were obtained. The impedance indexes of the obstructed and unobstructed kidney were compared for each patient.

RESULTS

The mean arterial resistive indexes of the obstructed kidneys were larger than those of the unobstructed kidneys, 0.67 +/- 0.08 and 0.62 +/- 0.05, respectively (p = 0.05). The venous impedance indexes comparing obstructed and unobstructed sides were 0.38 +/- 0.25 and 0.80 +/- 0.25, respectively, a statistically significant result (p = 0.0002). On average, the peak venous flow signal in the obstructed kidney was 69% higher than that of the unobstructed kidney (p = 0.04) and 86% higher than that of the peak venous flow signal in the control group (p = 0.005).

CONCLUSION

Renal obstruction alters the venous flow to a greater extent than the arterial flow, and a comparison between the venous flow in the obstructed and unobstructed kidneys may improve diagnostic accuracy.

Resistive index: an experimental study of the effects of diuretic stimulation in the unobstructed porcine kidney

OBJECTIVE

To study the effects of diuretic stimulation with frusemide and mannitol on the renal resistive index (RI) of the undilated unobstructed porcine kidney.

MATERIALS AND METHODS

Experiments were carried out on 14 pigs divided into two equal groups (A and B), under general anaesthesia. In all pigs both ureters were catheterized, thereby allowing urine output to be measured on each side separately, and an indwelling catheter in a femoral artery used to continuously measure the systemic blood pressure. Furthermore, in five pigs from each group, right renal blood flow was measured by ultrasonic flow probes placed around the renal arteries. The right kidney RI was measured at baseline and at 5-min intervals after frusemide (group A) and mannitol (group B) stimulation, for 75 min.

RESULTS

Frusemide caused significant increases in diuresis (P < 0.001) and renal blood flow (P = 0.009). This was accompanied by a significant decrease in mean arterial pressure (P < 0.001). The RI was unaffected (P = 0.706), with mean values in group A of 0.58-0.65. Mannitol also caused a significant increase in diuresis (P < 0.001) and a subtle but significant decrease in mean arterial pressure (P < 0.001). However, renal blood flow was unaffected by the diuretic (P = 0.820); the mean RI values were unaffected, at 0.61-0.66 (P = 0.375).

CONCLUSIONS

These results show that diuretic stimulation with frusemide or mannitol does not affect the RI of the unobstructed undilated porcine kidney, despite significant changes in diuresis, renal blood flow and mean arterial pressure.

Obstructive uropathy

There have been a significant number of advances in the understanding of the pathophysiology of obstructive uropathy. Of particular interest are the molecular biologic advances with respect to apoptosis, TGF-beta and the definition of the expression of certain genes. Research in the developing kidney in the fetus as it is affected by obstructive uropathy has had no significant advances in the past year.