Diagnostic value of diuretic-enhanced excretory MR urography in patients with obstructive uropathy

PURPOSE: Ultrasonography and conventional intravenous urography are most common methods in diagnosis of obstructive uropathies. The disadvantage of ultrasonography is inability of visualizing middle and lower one thirds of ureter, while intravenous urography is using radiation, also functionally extra loading effect on kidneys. In this study, the diagnostic value of MR urography on obstructive uropathy were investigated. MATERIALS AND METHODS: Forty five patients who were suffered from obstructive uropathy examined by ultrasonography, intravenous urography and diuretic-enhanced excretory MR urography by using MR-contrast-agent. RESULTS: MR urography established accuracy rate of 92.8% for stone diseases which formed the largest group in this study, however, in other causes of obstructive uropathy, MR urography provide 100% correct diagnosis. CONCLUSION: MR urography provide high quality images for diagnosing and determining causes of urinary obstruction defining position and severity of dilatations as well as showing localization of the pathology. We think that MR urography should be a primary investigation in patients with obstructive uropathy who have contrast agent and X-ray contrindication.     

Pulsed and continuous Doppler evaluation of renal dysfunction after kidney transplantation

Seventy-eight recipients, average age 36 years, of cadaver kidneys were studied to evaluate the usefulness of Doppler ultrasonography for diagnosis of common complications in renal transplant patients. The patients were divided in five groups: Control (normal renal function), acute rejection (AR), acute tubular necrosis (ATN), obstructive uropathy (OU) and pathological vasculature (PV); renal artery stenosis (RAS) and renal artery thrombosis (RAT). Pulsed Doppler ultrasonography (PDUS) was an effective method to diagnose RAS and RAT, but did not sufficiently differentiate between AR and ATN. Despite this, PDUS may be useful for follow-up of renal transplant patients as specific changes in the PDUS curves or differences in successively recorded patterns indicate abnormality, which may initiate more specific diagnostic methods.     

Nondilated obstructive uropathy: percutaneous nephrostomy performed to reverse renal failure

Ureteral obstruction can lead to renal failure without involving detectable dilatation of the calyces, renal pelvis, or ureter proximal to the obstruction. This phenomenon was noted in seven patients who had clinical obstruction that we were not able to diagnose using computed tomography (CT) or ultrasonography (US). These patients underwent percutaneous nephrostomy (PCN), which resulted in brisk diuresis and improved renal function. We obtained an accompanying antegrade urogram in these cases, which demonstrated the level of obstruction and indicated that dilatation of the collecting system was minimal or not present. When obstructive uropathy is suspected, we believe it is essential to consider performing PCN to evaluate and potentially reverse renal failure, even when CT and US scanning do not demonstrate obstruction.     

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.     

Radionuclides in the evaluation of urinary obstruction

Radionuclide renography and renal scanning techniques are ideally suited to the initial and follow-up evaluation of patients with obstructive uropathy. While other modalities are superior in their ability to provide anatomic information, the radionuclide study yields functional information for each kidney without the necessity to resort to invasive studies. In addition, the Nuclear Medicine study is well suited to the evaluation of obstruction where serial studies often are required because of a lower radiation burden compared to urography. This lower radiation dose is especially important in obstruction because of the recurrent nature of several kinds of obstructive uropathy and because of the high incidence in the pediatric age group. The ability to control urine flow rate during the procedure through dehydration or administration of diuretics is an additional benefit. Increasing availability of computerization of nuclear medicine procedures as well as interest in studies employing physiologic intervention (including the diuresis renogram) have assured an important place for radionuclide studies in the evaluation of patients with urinary obstruction.     

Renal colic: diagnosis and outcome.

To assess whether ultrasonography (US) with or without plain abdominal radiography (kidney, ureter, bladder [KUB] radiography) can replace intravenous urography (IVU) in detection of acute urinary tract obstruction, 101 consecutive patients with renal colic were evaluated with US followed immediately by IVU. Receiver operating characteristic (ROC) curves for US diagnosis of acute urinary tract obstruction yielded sensitivities of 91% and 92% for two reviewers at a specificity of 90%. There was no statistically significant difference between US and IVU results. When US was combined with KUB radiography, ROC curves yielded sensitivities of 94% and 97% for two reviewers at a specificity of 90%.KUB radiography alone was of limited diagnostic value. For US alone, no false-positive results occurred, and the false-negative results (n = 9 and n = 6 for two reviewers) were encountered in cases of grade 1 hydronephrosis and nondilated obstructive uropathy. The authors conclude that US combined with KUB radiography can replace IVU in initial evaluation and follow-up of the great majority of patients with renal colic.     

Detection of obstructive uropathy by bone scintigraphy

We prospectively evaluated routine bone scintigraphs to determine the prevalence of radiotracer retention in the renal collecting system, and to test the reliability of this finding as an indicator of obstructive uropathy. Post-diuretic renal washout was also measured, to evaluate the use of this procedure after bone scintigraphy. Stasis occurring only in the supine position was excluded by obtaining upright images. The findings on bone scintigraphy were compared with the results of renal sonography. Patients showing persistent pelvicaliceal concentration in the upright position after bone scintigraphy were found to have evidence of obstructive uropathy by sonography or other studies. Furosemide administration was followed by washout of the bone tracer from all kidneys with proven partial ureteral obstruction. Persistent renal pelvicaliceal concentration, in upright images after bone scintigraphy, appears to be a reliable indicator of obstructive uropathy. However, measurement of post-diuretic renal washout, after bone scintigraphy, does not reliably detect obstructive uropathy, and may be misleading if interpreted in the same way as the standard diuretic renogram.     

Applications of nuclear medicine in genitourinary imaging

Major advances in nuclear medicine instrumentation and radiopharmaceuticals for renal studies have occurred during the last decade. Current nuclear medicine methodology can be applied for accurate evaluation of renal function and for renal imaging in a wide variety of clinical situations. Total renal function can be estimated from the plasma clearance of agents excreted by glomerular filtration or tubular secretion, and individual function can be estimated by imaging combined with renography. A major area of radionuclide application is in the evaluation of obstructive uropathy. The introduction of diuretic renography and the use of computer-generated regions of interest offer the clinician added useful data which may aid in diagnosis and management. Imaging is of proven value also in trauma, renovascular hypertension, and acute and chronic renal failure. Methods for the evaluation of residual urine, vesicoureteral reflux, and testicular torsion have achieved increasing clinical use. These many procedures assure a meaningful and useful role for the application of nuclear medicine in genitourinary imaging.     

Applications of nuclear medicine in genitourinary imaging

Major advances in nuclear medicine instrumentation and radiopharmaceuticals for renal studies have occurred during the last decade. Current nuclear medicine methodology can be applied for accurate evaluation of renal function and for renal imaging in a wide variety of clinical situations. Total renal function can be estimated from the plasma clearance of agents excreted by glomerular filtration or tubular secretion, and individual function can be estimated by imaging combined with renography. A major area of radionuclide application is in the evaluation of obstructive uropathy. The introduction of diuretic renography and the use of computer-generated regions of interest offer the clinician added useful data which may aid in diagnosis and management. Imaging is of proven value also in trauma, renovascular hypertension, and acute and chronic renal failure. Methods for the evaluation of residual urine, vesicoureteral reflux, and testicular torsion have achieved increasing clinical use. These many procedures assure a meaningful and useful role for the application of nuclear medicine in genitourinary imaging.     

Present-day imaging of patients with renal colic

In the past decade alternatives to urography have been proposed for the study of patients with renal colic. In 1992 it was suggested to replace urography with KUB and ultrasonography. In 1993 the combination of KUB and ultrasonography followed by urography in unresolved cases was proposed and, in 1995, it was suggested to replace urography with unenhanced helical CT (UHCT). This article illustrates the contribution of UHCT to the study of patients with renal colic and analyses advantages and shortcomings of the technique compared with other diagnostic approaches. Diagnostics of the patient with renal colic is based on the detection of direct and indirect signs which allow identification of not only the calculus, with a sensitivity of 94–100 % and accuracy of 93–98 % according different authors, but also other signs that can serve to guide patient management and evaluate long-term prognosis. Unenhanced helical CT has the capability to detect extraurinary abnormalities which present with flank pain and mimic renal colic. The examination technique affects the quality of the images and therefore diagnostic accuracy as well as the dose to the patient. With regard to setting parameters, the choice of thickness and table feed should be guided by numerous factors. Multiplanar reconstruction is indicated in the study of the entire ureter course to identify the exact site of the calcification for the urologist to perform an evaluation similar to that obtained by urography. Many authors consider UHCT to be a valuable tool for suggesting the best therapeutic approach. Among these there are also urologists. The evaluation is based on the stone detection, its size and level in the urinary tract. Cost analysis shows that the cost of UHCT is equal to or inferior to the cost of urography. With regard to the dose, different data are reported in the literature. A high pitch (more than 1.5) and a thin collimation (3-mm thickness) are good compromise between quality and dose which can be compared to the dose of normal urography. What is to be done if helical CT is not available? If helical CT is not available, plain film plus ultrasonography should be considered. This approach does not solve all the cases; in unresolved cases urography is indicated. It should also be noted that US has a good sensitivity in detecting other conditions such as biliary lithiasis, acute pancreatitis, acute appendicitis and abdomino-pelvic masses which are responsible for pain that mimics renal colic. In conclusion, IVU should not have any more the priority in investigating the patients with renal colic. Helical CT should be the first choice in imaging a patient with renal colic. If this technique is not available, plain film and ultrasonography should be considered adding urography in unresolved cases.     

High dose urography: incidence and relationship to spontaneous peripelvic extravasation.

A prospective study was undertaken to determine the incidence of spontaneous extravasation of contrast in 82 patients with acute renal colic. The extravasation rate among 37 patients receiving 75 ml of contrast was 8.1%, while the rate among 45 patients receiving either 300 ml of 30% solution by infusion or a 140 ml bolus dose was 24.4%; overall the rate was 17%. Thus the incidence of extravasation was shown to increase with higher doses of contrast media. The primary dose in acute renal colic or other forms of obstructive uropathy should be in the low range (20-25 g 1-); reinjection after screening can be undertaken if necessary.     

Multidetector CT-urography in the study of urological complications in renal transplant

PURPOSE: To evaluate the value of CT-urography in the diagnosis and follow-up of the urological complications of renal transplantation. MATERIALS AND METHODS: We performed 19 CT-urography examinations (3 of which were follow-up) on 15 patients by using a spiral multislice CT scanner and multiplanar reconstructions. The examinations were carried out directly after administration of 100 ml of iodinated contrast medium by slow iv infusion, with acquisitions starting 5 minutes after the end of the infusion. Surgery was regarded as the gold standard for the diagnosis of urological complications in the operated patients, whereas in patients who had undergone medical therapy or stent placement the gold standard was 1 month ultrasound and clinical follow-up with evaluation of diuresis and renal function. RESULTS: Between January 1999 and December 2001 a total of 210 kidney transplantations were performed at our hospital. There were 34 urological complications in 28 patients with a 16.1% prevalence, consistent with the major international studies. The complications detected were 14 urine leaks and 19 ureteral obstructions secondary to stones, oedema, blood clots and stricture. We observed one case of reflux in the allograft ureter. Fourteen out of 16 CT-urography examinations yielded important clues for the diagnosis of urological complications in kidney allografts, completely replacing standard urography. In particular, CT-urography correctly detected 5 urinary fistulas by demonstrating iodinated contrast material leaks along the ureteral tract, and 8 cases of obstructive uropathy due to different causes (1 submucosal tunnel edema, 1 blood clot, 1 stone and 5 cases of ureteral stricture). One case of urinary fistula and one of obstructive uropathy were not detected. DISCUSSION AND CONCLUSIONS: CT-urography proved to be an important diagnostic tool in the evaluation of urological complications of kidney allografts, showing a diagnostic accuracy over 90%; it is useful for confirming the type and site of urological lesions, and therefore to provide guidance for a targeted surgical approach. Compared with excretory urography, which is no longer used in this diagnostic field, CT-urography is more complete and precise as it provides information not only about the urinary tract, but also about the kidney parenchyma and pararenal fluid collections. The only disadvantage, which limits its use to selected cases, is the risk associated with the use of iodinated contrast agents in patients with impaired renal function.     

Gastric cancer and obstructive uropathy

In recent 5 years, we have experienced 24 cases of advanced gastric cancer associated with obstructive uropathy. Included were 19 cases of undifferentiated, 3 cases of differentiated and 2 cases of unknown histological type. Obstructive uropathy is diagnosed based on the typical radiological findings such as dilatation and delayed demonstration of the upper collecting systems. Pathologically, undifferentiated type of gastric cancer had tendency to spread infiltrating along the vessels, nerves and the lymphatics without alteration of the ordinary anatomical structures. In such cases, mucosal surface of the urinary tract tended to be spared in spite of extensive tumor invasion. It was proven that several radiological findings were characteristic of urinary tract involvement secondary to gastric cancer. Either thread-like ureteral stricture by IVU or ring-like appearance of the ureter by CT is one of those typical findings. Renal sinus involvement may occur continuously to diffuse retroperitoneal invasion and it appears as a thickened wall of renal pelvis or soft tissue mass directly extending into the fatty tissue of renal sinus by CT. In such cases IVU has less diagnostic ability because of the lack of mucosal destruction. If the urinary bladder is involved, it typically shows chestnut-bur appearance by IVU and diffuse wall thickening by CT. In cases of advanced gastric cancer, particularly in cases of histologically undifferentiated type, CT and IVU images should be carefully interpreted in consideration of the infiltrative art of tumor extension.     

Differentialdiagnose fokaler Nierenläsionen in CT und MRT

The great majority of renal masses are found incidentally as a result of the use of ultrasonography, computed tomography (CT) and magnetic resonance imaging (MRI). If ultrasonography is not diagnostic CT or MRI should be initiated to differentiate lesions of the kidney that need surgical intervention from those that do not and from those that need follow-up examinations.Cystic renal masses are characterized by using the Bosniak classification, including category IIF. In solid lesions of the kidney first non-surgical lesions as well as lymphoma, renal infarction and nephritis should be excluded. Identifying fatty components in renal lesions is very important because in angiomyolipoma they are almost always present.CT and MRI are exellent for tumor detection. Careful evaluation of imaging finding combined with the patient′s history should assist the radiologist in making the proper diagnosis or recommending the appropriate treatment in most cases.This article provides a review about renal masses, the imaging methods for their evaluation and their characteristic features at CT and MR imaging. Different lesions are demonstrated like xantogranulomatous pyelonephritis, acute pyelonephritis, renal infarction, lymphoma, angiomyolipoma, renal oncocytoma, cystic lesion and polycystic disease the kidney, echinococcosis, renal cystadenoma, metastases, renal cell carcinoma (RCC), and multiple bilateral RCC in patients with Hippel-Lindau-Syndrome.This article should help to differentiate complex cystic lesions of the kidney by using the Bosniak-classification, especially Bosniak Category IIF. Solid masses should be characterized and the major question to be answered is whether the mass represents a surgical or nonsurgical lesion or if follow-up studies are necessary.     

Imaging evaluation of renal function: principles and limitations

The kidney performs multiple functions. Glomerular filtration is the most studied of these functions. In clinical practice, the surgical indication for patients with unilateral uropathy is frequently based on the split renal function as demonstrated by scintigraphy. MRI is not yet validated as a technique but nonetheless offers an interesting non-radiating alternative to achieve both morphological and functional renal evaluation. Recent pulse sequences such as diffusion, arterial spin labeling, and blood oxygenation dependent imaging may also provide additional information. CT and US remain of limited value for the evaluation of renal function.     

ACR Appropriateness Criteria Indeterminate Renal Mass

Renal masses are increasingly detected in asymptomatic individuals as incidental findings. An indeterminate renal mass is one that cannot be diagnosed confidently as benign or malignant at the time it is discovered. CT, ultrasonography, and MRI of renal masses with fast-scan techniques and intravenous (IV) contrast are the mainstays of evaluation. Dual-energy CT, contrast-enhanced ultrasonography, PET/CT, and percutaneous biopsy are all technologies that are gaining traction in the characterization of the indeterminate renal mass. In cases in which IV contrast cannot be used, whether because of IV contrast allergy or renal insufficiency, renal mass classification with CT is markedly limited. In the absence of IV contrast, ultrasonography, MRI, and biopsy have some advantages. Owing to the low malignant and metastatic potential of small renal cell carcinomas (≤4 cm in diameter), active surveillance is additionally emerging as a diagnostic strategy for patients who have high surgical risk or limited life expectancy.The ACR Appropriateness Criteria are evidence-based guidelines for specific clinical conditions that are reviewed every 3 years by a multidisciplinary expert panel. The guideline development and review include an extensive analysis of current medical literature from peer-reviewed journals and application by the panel of a well-established consensus methodology (modified Delphi) to rate the appropriateness of imaging and treatment procedures. In those instances in which evidence is lacking or not definitive, expert opinion may be used to recommend imaging or treatment.     

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.     

MR urography of obstructive uropathy: diagnostic value of the method in selected clinical groups

The aim of the study was to evaluate the role of MR urography (MRU) in the diagnosis of obstructive uropathy in selected groups of patients. The groups involved following pathologies: calculi; strictures of ureteropelvic junction (UPJ); benign and malignancy-induced ureterostenosis. Sixty patients with clinical diagnosis of obstructive uropathy were subjected to static fluid MRU (sMRU) with the use of 3D turbo spin echo (TSE) sequence in a 0.5-T magnet. The examination was completed with conventional MR sequences and in 12 cases additionally with sequences after the administration of Gd-DTPA and excretory MRU. The results were compared with intravenous urography (IVU), CT, US, clinical and histopathological data. The degree of the urinary tract dilatation as well as the level and type of obstruction were estimated. In patients with urolithiasis sMRU correctly depicted the degree of ureterohydronephrosis in 85%, in cases of UPJ stenosis and malignancy-induced ureterostenosis in 100% and in the group of benign ureterostenosis in 91% of patients. Determination of obstruction level in patients with stones was adequate in 92% and in cases of non-calculous ureteral strictures in 100% of patients. The sMRU sequence alone could not specify the nature of obstruction except 1 case of bladder carcinoma. Filling defects in ureters visible on MR urograms were verified with IVU or CT to exclude intrinsic tumours. Completed with conventional MR sequences sMRU enabled the depiction of solid mass or infiltration in 83% cases of malignancy-induced ureterostenosis, and in the remaining groups of patients neoplastic process was excluded in 91%. In conjunction with excretory MRU and conventional MR images sMRU appears to be a highly useful technique in assessment of obstructive uropathy, especially that of non-calculous origin. Among different clinical applications MRU is superior in the evaluation of dilated urinary tract in altered anatomical conditions (e.g. in patients with ileal neobladder). Electronic Publication     

Urological and medical complications of renal transplant

Medical complications from renal transplant (acute tubular necrosis, acute rejection, chronic rejection) are mainly imaged with Doppler ultrasound to first exclude vascular or urological causes for renal function impairment. Once these causes are excluded, imaging features are nonspecific and imaging is mainly used for follow-up and biopsy remains essential. Urological complications include postsurgical collections, urinary fistulas, obstructive uropathy, vesicoureteric reflux, infections and malignancies. Imaging plays a leading role in the diagnostic and therapeutic management of these complications.     

Acute renal failure in children. An ultrasonographic-clinical study

Acute renal failure (ARF) may be due to obstructive uropathy or renal parenchymal disease. Twenty-five children with acute renal failure secondary to renal parenchymal disease underwent ultrasonographic examination of the kidneys. Changes of renal size and cortical echogenicity were correlated with renal function. All patients presented with bilaterally enlarged kidneys with the exception of those in the neonatal age group (12%). Improvement in renal function resulted in normalization of renal size. With regard to cortical echogenicity two groups were formed. Group A comprised 11 patients whose kidneys had the same echogenicity as the liver, while in group B the kidneys were more echogenic (14 patients). Cortical echogenicity was always increased. Determination of creatinine levels showed a statistically significant difference between group A (3.32 mg% +/- 1.40 S.D.) and group B (5.95 mg% +/- 1.96 S.D.), p less than 0.001. Changes in renal function were paralleled by rapid changes in renal size and cortical echogenicity.