Captopril renography in the diagnosis of renal artery stenosis: accuracy and limitations

Renal artery stenting for atherosclerotic renal artery stenosis identified in patients with coronary artery disease: Does captopril renal scintigraphy predict outcomes?

The authors evaluated the effectiveness of percutaneous renal revascularization (PRR) with stenting for the treatment of atherosclerotic renal artery stenosis (ARAS) in patients with coronary artery disease and the usefulness of captopril renal scintigraphy for predicting clinical outcomes after PRR. Sixty-four consecutive patients, referred for evaluation of suspected ARAS, after coronary angiography, underwent baseline captopril renal scintigraphy followed by renal angiography. Forty-four patients (68.7%) were diagnosed with a significant ARAS≥ 60% and were treated with PRR plus medical therapy. Twenty-four months after PRR, 86.4% and 73.3% of patients showed a hypertension and renal benefit, respectively. Captopril renal scintigraphy positivity had moderate sensitivity and high specificity in predicting a hypertension and renal benefit. In patients with ARAS≥ 70%, the sensitivity and specificity were 100% for both a hypertension and renal benefit.PRR for ARAS conferred a substantial benefit in patients with a high coronary artery disease burden. Captopril renal scintigraphy was highly accurate in predicting clinical outcomes.

Positive Captopril Renography Without Renal Artery Stenosis but a Renal Cell Carcinoma

A positive captopril renography indicates that patient's hypertension is renin dependent, most commonly caused by renal artery stenosis. The authors reported a case of positive captopril renography; however, CT demonstrated that renal arteries were intact, but there was a huge chromophobe renal cell carcinoma. Renin-dependent hypertension was relieved soon after nephrectomy. It is an uncommon cause of positive captopril renography.

Plasma Renin Activity Predicts the Improvement in Resistant Hypertension after Percutaneous Transluminal Renal Artery Angioplasty

Objective Percutaneous transluminal renal artery angioplasty (PTRA) has been recommended for the treatment of renovascular resistant hypertension. However, large randomized trials have reported that PTRA did not improve the outcomes compared with optimal medical therapy in patients with renal artery stenosis (RAS). It is important to identify patients with renovascular hypertension who are likely to respond to PTRA. We herein examined whether or not the plasma renin activity (PRA) could predict the improvement in resistant hypertension after PTRA for RAS. Methods and Results A total of 40 patients (mean age: 63±15 years) with unilateral RAS who received PTRA for resistant hypertension were enrolled in this study. Twenty-two (55%) patients experienced a significant reduction in their blood pressure while using few antihypertensive agents at the 3-month follow up. The median PRA was significantly higher in patients using few antihypertensive agents than in those using more [4.2 ng/mL/hr, interquartile range (IQR) 2.6-8.0 vs. 0.8 ng/mL/hr, IQR 0.4-1.7, p<0.001]. To predict the improvement in hypertension after PTRA, a receiver operating characteristic analysis determined the optimal cut-off value of PRA to be 2.4 ng/mL/hr. A multivariate logistic regression analysis showed that higher PRA (>2.4 ng/mL/hr) was an independent predictor of the improvement in hypertension after PTRA (odds ratio: 22.3, 95% confidence interval: 2.17 to 65.6, p<0.01). Conclusion These findings suggest that the evaluation of preoperative PRA may be a useful tool for predicting the improvement in resistant hypertension after PTRA for patients with RAS.

Clinical problems in renovascular disease and the role of nuclear medicine

Although renovascular disease remains defined as a stenosis of the main renal artery or its proximal branches (renal artery stenosis [RAS]), its clinical overview has changed dramatically over the last 15-20 years and its management is more controversial than ever before. The clinical problems, not only diagnosis and treatment but also the relative contribution of different pathophysiological mechanisms involved in the progression of kidney disease, have shifted dramatically. This presentation aims to emphasize the paradigm change revisiting the (recent) past focused on renovascular hypertension (RVH) to the current context of preservation or recovery of threatened renal function in patients with progressive atherosclerotic renovascular disease until its last stage of irreversible "ischemic nephropathy." In the past, the foreground was occupied by RVH, a very rare disease, where the activation of the renin-angiotensin-aldosterone system (RAAS) was supposed to play the major, if not only, role in RVH issues. The retrospective RVH diagnosis was established either on the improvement or, more rarely, on the cure of hypertension after revascularization by, most often, a percutaneous transluminal renal angioplasty with or without a stent placement. At this time, captoptril radionuclide renography was an efficient diagnostic tool, because it was a functional (angiotensin-converting enzyme inhibition), noninvasive test aiming to evidence both the RAAS activation and the lateralization (or asymmetry) of renin secretion by the kidney affected by a "hemodynamically significant" RAS. At present, even if captoptril radionuclide renography could be looked upon as the most efficient (and cost effective in selected high-risk patients) noninvasive, functional test to predict the improvement of hypertension after RAS correction, its clinical usefulness is questioned as the randomized, prospective trials failed to demonstrate any significant benefits (either on blood pressure control or on renal function protection) of the revascularization over current antihypertensive therapy. Today many patients with RVH remain undetected for years because they are treated successfully and at low expense with these new blockers of RAAS. In addition to its well-known role in hemodynamics, angiotensin II promotes activations of profibrogenic and inflammatory factors and cells and stimulates reactive oxygen species generation. The "atherosclerotic milieu" itself plays a role in the loss of renal microvessels and defective angiogenesis. After an "adaptative" phase, ischemia eventually develops and induces hypoxia, the substratum of ischemic nephropathy. Because blood oxygen level-dependent MRI may provide an index of oxygen content in vivo, it may be useful to predict renal function outcome after percutaneous transluminal renal angioplasty. New PET tracers, dedicated to assess RAAS receptors, inflammatory cell infiltrates, angiogenesis, and apoptose, would be tested in this context of atherosclerotic renovascular disease.

Diagnostic criteria for renovascular disease: where are we now?

Renovascular disease, especially atherosclerotic renal artery stenosis (ARAS) in older subjects, is commonly encountered in clinical practice. This is at least in part due to the major advances in non-invasive imaging techniques that allow greater diagnostic sensitivity and accuracy than ever before. Despite increased awareness of ARAS, renal revascularization is less commonly performed, likely as a result of several prospective, randomized, clinical trials which fail to demonstrate major benefits of renal revascularization beyond medical therapy alone. Primary care physicians are less likely to investigate renovascular disease and nephrologists likely see more patients after a period of unsuccessful medical therapy with more advanced ARAS. The goal of this review is to revisit current diagnostic and therapeutic paradigms in order to characterize more clearly which patients will likely benefit from further evaluation and intensive treatment of renal artery stenosis.

Clinical Use of Laboratory Tests for the Identification of Secondary Forms of Arterial Hypertension

The prevalence of secondary hypertension can be underestimated if appropriate tests are not performed. The importance of selecting patients with a high pre-test probability of secondary forms of hypertension is first discussed. The laboratory tests currently used for seeking a cause of hypertension are critically reviewed, with emphasis on their operative features and limitations. Strategies to identify primary aldosteronism, the most frequent form of secondary hypertension, and to determine its unilateral or bilateral causes are described. Treatment entails adrenalectomy in unilateral forms, and mineralocorticoid receptor blockade in bilateral forms. Renovascular hypertension is also a common, curable form of hypertension, that should be identified as early as possible to avoid the onset of cardiovascular target organ damage. The tests for its confirmation or exclusion are discussed. The various tests available for the diagnosis of pheochromocytoma, which is much rarer than the above but extremely important to identify, are also described, with emphasis on recent developments in genetic testing. Finally, the tests for diagnosing some rarer monogenic forms and other renal and endocrine causes of arterial hypertension are explored.

Comparative Accuracy of Renal Duplex Sonographic Parameters in the Diagnosis of Renal Artery Stenosis: Paired and Unpaired Analysis

OBJECTIVE

The purpose of this study was to evaluate the test performance of duplex sonographic parameters in screening for hemodynamically significant renal artery stenosis, which occurs in approximately 5% of persons with hypertension.

MATERIALS AND METHODS

A comprehensive literature search was conducted to find studies on the diagnosis of renal artery stenosis in which duplex sonography and intraarterial angiography were compared and in which sensitivity and specificity were calculated. MEDLINE (1966-2005), EMBASE (1988-2005), and reference lists were searched and the authors contacted. Data were subjected to meta-analysis according to the hierarchical summary receiver operating characteristic curve model. Heterogeneity in test performance relating to population and design features was investigated.

RESULTS

From 1,357 titles, 88 studies involving 9,974 arteries in 8,147 patients were included. The following four parameters were evaluated: peak systolic velocity (21 studies), acceleration time (13 studies), acceleration index (13 studies), and renal-aortic ratio (13 studies). The corresponding diagnostic odds ratios (ORs) were 60.9 (95% CI, 28.3-131.2), 28.9 (95% CI, 7.1-117.2), 16.0 (95% CI, 5.1-50.6), and 29.3 (95% CI, 12.7-67.7). Results based on studies in which parameters were directly compared showed that peak systolic velocity had greater accuracy than renal-aortic ratio (relative diagnostic OR, 1.8; p = 0.03; nine studies) and acceleration index (relative diagnostic OR, 5.3; p < 0.001; five studies). Acceleration time versus acceleration index showed no evidence of a difference in accuracy (relative diagnostic OR, 1.1; p = 0.65; nine studies). Analysis of peak systolic velocity used in combination with other parameters compared with peak systolic velocity alone (seven studies) showed evidence of a shift in test positivity (p < 0.001) but only weak evidence of improvement in accuracy (relative diagnostic OR, 1.6; p = 0.09).

CONCLUSION

Sonography is a moderately accurate screening test for renal artery stenosis. The single measurement, peak systolic velocity, has the highest performance characteristics, an expected sensitivity of 85% and specificity of 92%. Additional measurements do not increase accuracy.

Atherosclerotic renal artery stenosis and renovascular hypertension: clinical diagnosis and indications for revascularization

Atherosclerotic renal artery stenosis (RAS) is relatively common and often associated with reversible hypertension, progressive renal insufficiency, and/or coronary-independent pulmonary edema. Not all RAS is associated with renovascular hypertension. Historical and physical findings may suggest renovascular hypertension and warrant investigation for RAS. Noninvasive diagnostic imaging options include renal artery duplex ultrasonography, magnetic resonance angiography, computed tomographic angiography, and CO2 angiography, with each method having its own advantages and limitations. Functional tests of renal flow, which characterize RAS significance, include captopril-stimulated plasma renin activity and captopril renography. To date, no single approach has shown clear superiority either in diagnosis or identification of patients most likely to benefit from revascularization. Revascularization of RAS is recommended for severe/drug-refractory hypertension, preservation of renal function, recurrent flash pulmonary edema, or recurrent severe heart failure. Intervention response is variable, but the ongoing Cardiovascular Outcomes in Renal Atherosclerotic Lesions (CORAL) trial, comparing medical therapy with and without stenting, should provide management guidance.

Interpretation of captopril renography using artificial neural networks

The purpose of this study was to develop a method based on artificial neural networks for interpretation of captopril renography tests for the detection of renovascular hypertension caused by renal artery stenosis and to assess the value of different measurements from the test. A total of 250 99mTc-MAG3 captopril renography tests were used in the study. The material was collected from two different patient groups. One group consisted of 101 patients who also had undergone a renal angiography. The angiographies, which were used as gold standard, showed a significant renal artery stenosis in 53 of the 101 cases. The second group consisted of 149 patients, who's captopril renography tests all were interpreted as not compatible with significant renal artery stenosis by an experienced nuclear medicine physician. Artificial neural networks were trained for the diagnosis of renal artery stenosis using eight measures from each renogram. The neural network was then evaluated in separate test groups using an eightfold cross validation procedure. The performance of the neural networks, measured as the area under the receiver operating characteristic curve, was 0.93. The sensitivity was 91% at a specificity of 90%. The lowest performance was found for the network trained without use of a parenchymal transit measure, indicating the importance of this feature. Artificial neural networks can be trained to interpret captopril renography tests for detection of renovascular hypertension caused by renal artery stenosis. The result almost equals that of human experts shown in previous studies.

Two cases of renovascular hypertension and ischemic renal dysfunction: reliable choice of examinations and treatments

We experienced two aged patients with atherosclerotic renovascular stenosis associated with hypertension and ischemic nephropathy. Both patients exhibited sudden rise in blood pressure (BP) and progressive aggravation of renal dysfunction. In these patients, the use of contrast medium to screen for renal artery stenosis (RAS) ran the risk of further deterioration of renal function. We therefore used magnetic resonance angiography (MRA), which is less conducive to renal damage, to screen for RAS. One-sided RAS was treated by percutaneous transluminal angioplasty of the renal artery (PTRA) and stenting. As a result, BP decreased in both patients. Serum creatinine (Cr) decreased slightly in one patient, whereas, in the other, serum Cr increased transiently and then decreased and stabilized to pre-treatment levels. Thus, although it is unclear whether the combination of PTRA and stenting is among the best treatments for patients with RAS and moderate-to-severe renal dysfunction, PTRA and stenting are clearly of benefit in selected patients. In addition, recent progress in characterizing the pathophysiology of ischemic nephropathy associated with renovascular hypertension has created interest in the therapeutic potential of angiotensin II receptor antagonists, sympatholytic agents, and antioxidants. Therefore, we discuss the therapeutic utility of PTRA and stenting and the above-mentioned medications in patients with RAS and renal dysfunction.

Reversible Renin-dependent Renovascular Hypertension Successfully Treated With Percutaneous Transluminal Renal Angioplasty and Stenting

A 37-year old woman was suspected of having renovascular hypertension because of recent onset severe hypertension (blood pressure 220/135 mmHg; compared to 132/65 mmHg two years earlier) and an abdominal bruit. A captopril renal scan indicated the presence of right renal artery stenosis. Additionally, a captopril plasma renin activity (PRA) provocation test showed a positive result for renovascular hypertension (baseline PRA = 291 microU/mL; 1 hour post-captopril PRA = 1444 microU/mL). Selective renal angiography demonstrated a severe critical stenotic lesion at the distal portion of the right renal artery. Blood pressure (BP) decreased to 136/80 mmHg one day after successful percutaneous transluminal renal angioplasty and stenting. Repeat renal angiography six months after the procedure revealed no evidence of in-stent restenosis. Blood pressure (BP = 137/76 mmHg) and plasma renin profile (baseline PRA = 23.8 microU/mL; 1 hour post-captopril PRA=22.3 microu/mL) also were normal six months following initial revascularization. Moreover, blood pressure (137/84 mmHg) and renin profile remained normal 2.5 years after the procedure (baseline PRA = 24.3 microU/mL; 1 hour post-captopril = 25.6 microU/mL). The results of this study have thus demonstrated a case of renin-dependent renovascular hypertension in which both the blood pressure and plasma renin activity profile normalized following successful percutaneous transluminal angioplasty and stenting.

Long-term outcome after surgical kidney revascularization for fibromuscular dysplasia and atherosclerotic renal artery stenosis

PURPOSE

At a time of minimally invasive surgery in urology, the role of surgical kidney revascularization in the management of renal artery disease has changed during the last decade. Our experience with surgical kidney revascularization, and the long-term clinical outcomes of fibromuscular dysplasia (FMD) and atherosclerotic renal artery stenosis are reviewed.

MATERIALS AND METHODS

The study group comprised 140 patients with renovascular hypertension, 72 with FMD and 68 with atherosclerotic renal artery disease, who underwent surgical revascularization between 1982 and 1999. The indications for surgical revascularization were the treatment of hypertension and the preservation of renal function in 17 patients with renal artery occlusion, 55 with ostial stenosis, 52 with branch stenosis, 6 with bilateral artery stenosis, 7 with solitary kidney renal artery stenosis and 3 with solitary kidney renal artery occlusion.

RESULTS

Postoperative blood pressure and renal function were monitored for 1 to 17 years (mean 11.3). Long-term blood pressure control was observed in 93% of patients with FMD and in 71% of those with atherosclerosis. Improvement or stabilization of renal function was observed in 92% of patients with FMD and in 68% of those with atherosclerosis. The preoperative estimated glomerular filtration rate compared to postoperative was significantly increased in both groups.

CONCLUSIONS

Surgical kidney revascularization is effective in secondary hypertension with a high long-term efficacy in the normalization of blood pressure and in the preservation of renal function, especially in patients with a solitary or 1 functional kidney.

Utility of a 0.014" pressure-sensing guidewire to assess renal artery translesional systolic pressure gradients

Renal ischemia due to renal artery stenosis (RAS) is an important cause of secondary hypertension and renal insufficiency. Several methods are available to diagnose RAS; however, the identification of clinically significant lesions remains problematic. We measured the translesional systolic pressure gradient (TSPG) with a 4 Fr catheter and a 0.014" pressure-sensing guidewire and compared these data to angiographic findings. The TSPG obtained by pressure-sensing guidewire correlated more strongly with angiographic minimal lumen diameter (r(2) = 0.801) than those obtained by 4 Fr catheter (r(2) = 0.360). The relationship of TSPG with percent stenosis was not strong, regardless of the method used (r(2) = 0.228 with pressure-sensing guidewire, 0.358 with 4 Fr catheter). Using a 0.014" pressure-sensing guidewire is effective for assessing TSPG and provides a more reliable indication of stenosis significance than use of a 4 Fr catheter.

The diagnosis and management of renovascular disease: a primary care perspective. Part I. Making the diagnosis

Renovascular disease is a complex disorder, the most common causes of which are fibromuscular dysplasia and atherosclerotic disease. It usually presents in one of three forms: asymptomatic renal artery stenosis, renovascular hypertension, or ischemic nephropathy. This complexity often makes diagnostic and management decisions difficult. This review will be presented in two parts. In Part I, the authors will discuss when to consider and how to go about making the diagnosis. In Part II (in a future issue of The JCH), the authors discuss the management of renovascular disease. The clinical index of suspicion remains paramount in setting the diagnostic strategy. Although it is subject to certain limitations, conventional contrast angiography is usually considered the gold standard in confirming the diagnosis. In addition, there are a number of available noninvasive tests that can aid in decision making. These tests can be divided into those that detect the anatomic presence of a stenosis and those that identify the functional consequences of the renal artery obstruction. No one study is appropriate for every patient. A diagnostic algorithm is proposed at the conclusion of this review.

Is it necessary to study accessory arteries when screening the renal arteries for renovascular hypertension?

PURPOSE

To determine the prevalence of isolated hemodynamically significant stenoses of accessory renal arteries when the main renal arteries are patent.

MATERIALS AND METHODS

In 68 adults (24 men, mean age, 67 years +/- 10; 44 women, mean age, 67 years +/- 12), angiograms that fulfilled the following criteria were studied: (a) technically adequate renal angiograms obtained to evaluate suspected renovascular hypertension and (b) angiographically documented hemodynamically significant stenosis of any renal artery. The percentage of kidneys and the percentage of patients with hemodynamically significant isolated stenoses of accessory renal arteries were calculated.

RESULTS

Eighty-seven kidneys in 68 patients had hemodynamically significant renal artery stenoses. Fifteen kidneys had 16 accessory renal arteries. Four accessory arteries in three patients had hemodynamically significant stenoses. Only one of 68 patients (1.5%) had an accessory artery stenosis unaccompanied by a main renal artery stenosis in either kidney; this patient had bilateral hemodynamically significant accessory artery stenoses. Two patients had coexistent hemodynamically significant stenoses of accessory and main renal arteries.

CONCLUSION

The prevalence of a hemodynamically significant stenosis isolated to an accessory renal artery was 1.5% in our study. Thus, failure to detect accessory renal arteries should not unduly affect the utility of a noninvasive test for detecting renovascular hypertension.

Contemporary approach to diagnosis and evaluation of renovascular hypertension

Recommendations regarding the clinical protocols for radionuclides of choice and diagnostic criteria for renovascular hypertension have been established by the consensus report on captopril renography. A review of the existing data indicates that postcaptopril renography alone is a safe and effective means of noninvasively screening hypertensive patients. A normal radionuclide study after captopril suggests with a reasonable degree of certainty that potentially reversible renovascular hypertension is unlikely. A positive study in an appropriately screened hypertensive patient with preserved renal function suggests renovascular disease is likely with a sensitivity and specificity in excess of 90%. In the comparative studies of Elliott and Miralles and colleagues, captopril renography was a more sensitive and specific screening test than the captopril plasma renin activity test. Although there may be confounding variables, such as renal dysfunction, medications, and types of stenosis, a positive captopril renogram may suggest a cure or improvement in blood pressure control with successful intervention such as PTRA or revascularization. Whether captopril renography can predict stabilization of individual kidney function is speculative and deserving of further study.

Techniques for predicting a favourable response to renal angioplasty in patients with renovascular disease

Renovascular disease is present in some 10-40% of patients with end-stage renal disease, and constitutes the fastest-growing group of end-stage renal disease patients. The unselective correction of renal artery stenosis has led to disappointing results. Most studies that compared conservative treatment with angioplasty found only modest or no beneficial effects of angioplasty on renal function and blood pressure. It is therefore mandatory to evaluate the functional significance of a stenosis before intervention. Patients with a high likelihood of a favourable response should be identified. Factors that affect outcome include the severity of renal artery stenosis, the procedure used to treat renal artery stenosis (antihypertensive drugs, angioplasty with or without stenting, or surgery), radiocontrast nephrotoxicity, atheroembolism and, most importantly, underlying renal disease, forestalling a favourable response of renal function or blood pressure even after the successful correction of renal artery stenosis. Evaluation of the renal resistance index using Doppler ultrasound or captopril scintigraphy are the best methods by which to classify patients as responders or non-responders to intervention. Each factor has to be considered before the correction of renal artery stenosis to achieve satisfactory results with regard to an improvement in renal function and blood pressure.

Detection of renal artery stenosis: prospective comparison of captopril-enhanced Doppler sonography, captopril-enhanced scintigraphy, and MR angiography

OBJECTIVE

The objective of our study was to compare the value of captopril-enhanced Doppler sonography, captopril-enhanced renal scintigraphy, and gadolinium-enhanced MR angiography for detecting renal artery stenosis.

SUBJECTS AND METHODS

Forty-one patients with suspected renovascular hypertension were prospectively examined with captopril-enhanced Doppler sonography, captopril-enhanced renal scintigraphy, gadolinium-enhanced MR angiography, and catheter angiography. The sensitivity and specificity of each technique for detecting renal artery stenosis measuring 50% or greater and 70% or greater were compared using the McNemar test. Positive and negative predictive values were estimated for populations with 5% and 30% prevalence of renal artery stenosis. Kappa values for interobserver agreement were assessed for both gadolinium-enhanced MR angiography and catheter angiography.

RESULTS

For detecting renal artery stenosis measuring 50% or greater, the sensitivity of gadolinium-enhanced MR angiography (96.6%) was greater than that of captopril-enhanced Doppler sonography (69%, p = 0.005) and captopril-enhanced renal scintigraphy (41.4%, p = 0.001). No significant difference in specificity was observed among modalities. For renal artery stenosis measuring 50% or greater, positive and negative predictive values were respectively 62% and 86% for captopril-enhanced Doppler sonography, 49% and 76% for captopril-enhanced renal scintigraphy, and 53% and 98% for gadolinium-enhanced MR angiography. Interobserver agreement was high for both gadolinium-enhanced MR angiography (kappa = 0.829) and catheter angiography (kappa = 0.729).

CONCLUSION

Gadolinium-enhanced MR angiography is the most accurate noninvasive modality for detecting renal artery stenosis greater than or equal to 50%. The use of captopril-enhanced Doppler sonography in combination with gadolinium-enhanced MR angiography for identifying renal artery stenosis needs to be evaluated with a cost-effectiveness analysis.

Resistance to antihypertensive medication as predictor of renal artery stenosis: comparison of two drug regimens

BACKGROUND

Renal artery stenosis is among the most common curable causes of hypertension. The definitive diagnosis is made by renal angiography, an invasive and costly procedure. The prevalence of renal artery stenosis is less than 1% in non-selected hypertensive patients but is higher when hypertension is resistant to drugs.

OBJECTIVE

To study the usefulness of standardised two-drug regimens for identifying drug-resistant hypertension as a predictor of renal artery stenosis.

DESIGN AND SETTING

Prospective cohort study carried out in 26 hospitals in The Netherlands.

PATIENTS

Patients had been referred for analysis of possible secondary hypertension or because hypertension was difficult to treat. Patients < or =40 years of age were assigned to either amlodipine 10 mg or enalapril 20 mg, and patients >40 years to either amlodipine 10 mg combined with atenolol 50 mg or to enalapril 20 mg combined with hydrochlorothiazide 25 mg. Renal angiography was performed: (1) if hypertension was drug-resistant, ie if diastolic pressure remained > or =95 mm Hg at three visits 1-3 weeks apart or an extra drug was required, and/or (2) if serum creatinine rose by > or =20 micromol/L (> or =0.23 mg/dL) during ACE inhibitor treatment.

RESULTS

Of the 1106 patients with complete follow-up, 1022 had been assigned to either the amlodipine- or enalapril-based regimens, 772 by randomisation. Drug-resistant hypertension, as defined above, was identified in 41% of the patients, and 20% of these had renal artery stenosis. Renal function impairment was observed in 8% of the patients on ACE inhibitor, and this was associated with a 46% prevalence of renal artery stenosis. In the randomised patients, the prevalence of renal artery stenosis did not differ between the amlodipine- and enalapril-based regimens.

CONCLUSIONS

In the diagnostic work-up for renovascular hypertension the use of standardised medication regimens of maximally two drugs, to identify patients with drug-resistant hypertension, is a rational first step to increase the a priori chance of renal artery stenosis. Amlodipine- or enalapril-based regimens are equally effective for this purpose.

Noninvasive investigation for renal artery stenosis: contrast-enhanced magnetic resonance angiography and color Doppler sonography as compared to digital subtraction angiography

INTRODUCTION

The question about the most appropriate non-invasive method for detecting a renal artery stenosis (RAS) when comparing contrast enhanced magnetic resonance angiography (MRA) and color Doppler sonography (CDS) is still under discussion. Therefore we conducted a prospective study in order to evaluate both methods as compared to digital subtraction angiography (DSA).

PATIENTS/METHODS

Thirtysix consecutive patients (53,9 +/- 13,7 years) with suspected RAS were investigated. MRA was performed using gadolinium for contrast enhancement. CDS was performed using a 2.5 and 3,5 MHz transducer. A peak systolic velocity (Vmax) >200 cm/sec within renal arteries and/or a side to side difference of the resistive index (RI) of >0,05 were used to discriminate stenosis. A diameter reduction of > or = 60% by DSA was considered a stenosis relevant to the patient.

RESULTS

Sixty-eight main renal arteries and 9 accessory vessels were detected by DSA. Twenty main and 3 accessory arteries were found to be stenosed > or = 60%, while 4 main and 1 accessory artery presented with occlusion. MRA detected 70 renal vessels (65 main and 5 accessory arteries). Twenty-one stenosed arteries and 4 occluded vessels were correctly diagnosed by MRA. With CDS 68 renal vessels (62 main and 6 accessory arteries) could be visual- ized out of which 21 stenoses were diagnosed because of increased Vmax and 6 stenoses were detected because of a side to side difference of RI. For main renal arteries sensitivities and specificities were 96% and 86% for MRA and 96% and 89% for CDS.

CONCLUSIONS

MRA and CDS are both comparable methods for detection of a renal artery stenosis > or = 60%. Despite several limitations, CDS can at the moment still be favored as a screening method.

Diuretic renography and angiotensin converting enzyme inhibitor renography

Renovascular hypertension and renal outlet obstruction are two clinical conditions well evaluated by nuclear medicine techniques. They both require a specific intervention to challenge a specific aspect of renal functional reserve. Diuretic renography is the oldest common example in nuclear medicine where functional change in the kidney is provoked for diagnostic purposes. The kidney's tubular functional reserve, in this instance, is challenged to induce diuresis and increase urine flow. This intervention permits diuretic renography to retain an essential role in the evaluation of hydroureteronephrosis. Captopril renography is a more recent example of a similar principle and depends on a reactive renin-angiotensin system to identify a kidney responsible for RVH. In both renal outlet obstruction and RVH, an anatomic abnormality is also identified (hydronephrosis and RAS, respectively) at some point in the diagnostic workup. The final diagnosis in each instance, however, depends on evidence for a functional disorder, provoked and measured during the radionuclide interventional examination. These serve as excellent examples of the power of functional imaging to identify specific medical disorders.

Captopril renography and the relevance of abnormal but bilateral identical curves in the diagnosis of renal artery stenosis

BACKGROUND

Captopril renography (CR) has been shown to improve the effectiveness of renal scintigraphy in renovascular hypertension, by inhibiting angiotensin-converting enzyme. CR is particularly sensitive and specific in unilateral renal artery stenosis (RAS), but results in patients with bilateral RAS are less favourable. The aim of this study was to investigate the meaning of abnormal but identical renographic curves in the diagnosis of RAS.

PATIENTS AND METHODS

One hundred and fifty-eight patients clinically suspected for renovascular hypertension underwent CR, using 50 MBq (99)Tc(m)-mercaptoacetyltriglycine ((99)Tc(m)-MAG(3)), prior to performing renal angiography. CR was performed 1 h after captopril administration. Renograms were analysed according to the consensus criteria. All patients underwent angiography, considered as the "gold standard" in the detection of the presence of RAS (stenosis >50% was defined as significant). All kidneys were categorized into three groups, scintigraphically as well as angiographically: no stenosis, unilateral stenosis and bilateral stenosis.

RESULTS

Out of 158 patients 100 (63%) showed a RAS on angiography (58 (37%) unilateral, 42 (26%) bilateral). The sensitivity and specificity of CR evaluated by patient was 83% and 75%, respectively. Thirty patients with completely identical curves were identified, 21 patients with normal curves and nine patients with abnormal identical curves. All but one patient showed no RAS on the angiogram. In this single patient a unilateral stenosis was found.

CONCLUSION

Identical curves on the renogram generally suggest no RAS and are probably due to intrinsic parenchymal disease.

[Current methods for diagnosing renal artery stenosis]

PURPOSE

Today, the methods for detecting renal artery stenosis are numerous. They lead to the identification either of anatomic stenosis or functional stenosis (onset of renin-angiotensin system). The purpose of this review is to emphasize the performances, limitations and diagnostic criteria for each technique.

CURRENT KNOWLEDGE AND KEY POINTS

For detection of anatomic stenosis, the feasibility of Doppler examination has been increased by the improvement of US systems and the development of contrast agents. However, the criteria used nowadays still need wider evaluation. Helical CT angiography allows a better detection of accessory arteries and calcifications but MR angiography has a better spatial resolution and uses a non-nephrotoxic contrast agent. The performances of these two techniques have never been compared. The choice between these techniques depends on the operators' experience and the availability of the systems. For functional stenosis, detection is now based on captopril-sensitized scintigraphy.

FUTURE PROSPECTS AND PROJECTS

It would be necessary to better compare performances and cost-effectiveness ratios of these methods and of the two imaging strategies (detection of anatomic stenosis versus functional stenoses). Probably in the future, MR will gain a major place, providing, in the same imaging session, morphologic and functional data.

Increasing the diagnostic yield of renal angiography for the diagnosis of atheromatous renovascular disease

Atheromatous renovascular disease (ARVD) is a common cause of hypertension and chronic renal failure (CRF). In this unit, intravenous digital subtraction angiography (DSA) (or intraarterial DSA if indicated) is used as a screening angiographic study when ARVD is suspected. However, increased use of these investigations has resulted in a longer waiting time for angiography. As the majority of studies are negative for ARVD, clinical features and results of investigations of patients undergoing angiography were reviewed to identify those having the greatest likelihood of ARVD. The clinical notes were reviewed for all 249 patients undergoing angiography over an 18-month period. Primary indications for investigation were: hypertension 71 (28.5%), CRF 156 (62.7%) and CRF with severe hypertension 22 (8.8%). 12 of the CRF patients had end-stage renal failure. 166 (66.7%) patients had no evidence of ARVD, while only 83 (33.3%) patients showed some degree of ARVD, 29 (35%) of which had bilateral renal artery disease. There was no significant difference between the ARVD group and the non-ARVD group for mean age (69.0 years vs 63.3 years), male to female ratio, history of smoking (68.7% vs 55.4%), severe hypertension (10.8% vs 9.0%), hypercholesterolaemia (61.4% vs 47.0%), diabetes mellitus (28.6% vs 25.3%) or angiotensin converting enzyme inhibitor-related renal dysfunction (9.6% vs 6.1%). More patients in the ARVD group were investigated for CRF than in the non-ARVD group, as reflected by the higher serum creatinine level and the lower creatinine clearance in the ARVD group. 55 (33.1%) of the non-ARVD patients had no comorbid vascular disease, vascular bruits or ultrasound discrepancy in the size of the two kidneys, whereas all ARVD patients had at least one of these features (negative predictive value 100%). All three features were present in 19.3% of ARVD patients but in only 3.0% of the non-ARVD patients (positive predictive value 76.2%, specificity 97%). We plan to rationalize the criteria for angiography in the light of these findings, anticipating an increase in the diagnostic yield of renal angiography from its current 33.3% to above 42%.

Use of Doppler ultrasonography to predict the outcome of therapy for renal-artery stenosis

BACKGROUND

Prospectively identifying patients whose renal function or blood pressure will improve after the correction of renal-artery stenosis has not been possible. We evaluated whether a high level of resistance to flow in the segmental arteries of both kidneys (indicated by resistance-index values of at least 80) can be used prospectively to select appropriate patients for treatment.

METHODS

We evaluated 5950 patients with hypertension for renal-artery stenosis using color Doppler ultrasonography, and we measured the resistance index ([1 - end-diastolic velocity divided by maximal systolic velocity] x 100). Among 138 patients who had unilateral or bilateral renal-artery stenosis of more than 50 percent of the luminal diameter and who underwent renal angioplasty or surgery, the procedure was technically successful in 131 (95 percent). Creatinine clearance and 24-hour ambulatory blood pressure were measured before renal-artery stenosis was corrected; 3, 6, and 12 months after the procedure; and yearly thereafter. The mean (+/-SD) duration of follow-up was 32+/-21 months.

RESULTS

Among the 35 patients (27 percent) who had resistance-index values of at least 80 before revascularization, the mean arterial pressure did not decrease by 10 mm Hg or more after revascularization in 34 (97 percent). Renal function declined (defined by a decrease in the creatinine clearance; of at least 10 percent) in 28 (80 percent); 16 (46 percent) became dependent on dialysis and 10 (29 percent) died during follow-up. Among the 96 patients (73 percent) with a resistance-index value of less than 80, the mean arterial pressure decreased by at least 10 percent in all but 6 patients (6 percent) after revascularization; renal function worsened in only 3 (3 percent), all of whom became dependent on dialysis; and 3 (3 percent) died (P<0.001 for the comparison with patients with a resistance-index value of at least 80).

CONCLUSIONS

A renal resistance-index value of at least 80 reliably identifies patients with renal-artery stenosis in whom angioplasty or surgery will not improve renal function, blood pressure, or kidney survival.

Tc-99m DTPA acetylsalicylic acid (aspirin) renography in the detection of renovascular hypertension

PURPOSE

Prostaglandins play important roles in renal physiology and in the development of renovascular hypertension. In a recent study, inhibition of renal prostaglandin synthesis was found to be useful for detecting renovascular hypertension using renal scintigraphy. In the current study, the authors evaluated the role of aspirin (an inhibitor of prostaglandin synthesis) and compared it with Tc-99m DTPA captopril renal scintigraphy (CS).

MATERIALS AND METHODS

Twenty-five patients were examined with Tc-99m DTPA in a three-step manner: a baseline study, CS, and aspirin scintigraphy (AS). Each scintigraphic study was interpreted visually and according to the renogram curve patterns. Semiquantitative parameters (Tmax, renal indices [%], 20-minute/max count ratio, glomerular filtration rate) were also calculated. Plasma renin activity was determined for each study. The blood pressures of all patients were measured during AS. All patients had a contrast-enhanced angiogram that was used as the reference test.

RESULTS

Three groups of patients were observed based on the scintigraphic and angiographic results. In each group, no difference was observed in blood pressure after aspirin administration. In group 1, seven patients had normal angiographic and scintigraphic results. In group 2, eight patients had angiographically confirmed renal artery stenosis (RAS). In 6 patients (mean, 47% RAS), both AS and CS were negative for RVH. In the remaining two patients with RAS (mean, 83% stenosis), the kidneys were atrophic on the stenotic side, and thus the kidneys did not respond to the interventions. No difference was observed in plasma renin activity in groups 1 and 2. Group 3 included 10 patients who had angiographically confirmed RAS (mean, 86%). In 9 patients, both CS and AS were positive for RVH. In the remaining one patient, scintigraphic results were falsely negative. Statistical analyses performed for semiquantitative parameters did not reveal any significant difference in this group, although there was a tendency toward prolonged Tmax values after captopril and aspirin administration. In four cases, unexpected elevation of plasma renin activity was observed in group 3.

CONCLUSIONS

These data indicate that AS with Tc-99m DTPA is an alternative for CS. It has the advantage of having no effect on blood pressure and does not require that angiotensin-converting enzyme inhibitors be discontinued. Although in this study 9 of 10 patients had correct diagnoses of RAS, further studies, especially using tubular agents with the calculation of parenchymal transit time, might provide valuable information in this patient group. An ongoing study is being performed in the authors' institute.

Hypertension

The current JNC-VI criteria for diagnosis and classification of hypertension are discussed. The laboratory evaluation of both essential and secondary hypertension is examined, and recommendations are made in this regard. Finally, the complications and treatment of essential hypertension and the causes and management of resistant hypertension are discussed.

Evaluation of duplex ultrasound and captopril renography for detection of renovascular hypertension

BACKGROUND

Renovascular hypertension is the most common form of curable secondary hypertension and, if untreated, may lead to end-stage kidney disease. Given that renal function and hypertension may improve after renal angioplasty, it is pertinent to identify patients with renal artery stenosis. The aim of the present study was to evaluate both duplex ultrasound and captopril renography for detection of renal artery stenosis among hypertensive patients.

METHODS

To avoid selection bias, all patients referred to our center for evaluation of renovascular hypertension were asked to participate in the study. Patients were examined by intra-renal duplex ultrasound (N = 121), measuring pulsatility index and acceleration of the blood flow during early systole. In 98 patients, 99mTc-DTPA captopril renography was performed in conjunction with duplex ultrasound. Renal angiography was performed in all patients regardless of the results of the noninvasive tests.

RESULTS

The prevalence of renal artery stenosis was 19%. In the 98 patients examined by both duplex ultrasound and captopril renography, sensitivity and positive predictive values for detection of a renal artery stenosis of 50% degree or more were 84 and 76%, respectively, for duplex ultrasound, whereas captopril renography was associated with a sensitivity and positive predictive value of 68% for both (P = NS). Specificity and negative predictive values were 94 and 96%, respectively, for duplex ultrasound, whereas the corresponding values for captopril renography were 92% for both (P = NS). Specificity and negative predictive values were 94 and 96%, respectively, for duplex ultrasound, whereas the corresponding values for captopril renography were 92% for both (P = NS).

CONCLUSIONS

Both duplex ultrasound and captopril renography are associated with high specificity and negative predictive values for detection of renal artery stenosis. Sensitivity and positive predictive values are at least as good for duplex ultrasound compared with captopril renography. Given that duplex ultrasound is easier to perform and more cost effective, we propose that it should be the method of first choice when screening for renal artery stenosis in a hypertensive population.

Individual kidney glomerular filtration rate in the interpretation of non-diagnostic curves on captopril renography

Captopril renography is known to have low sensitivity in the detection of renovascular disease in patients with bilateral renovascular disease and in patients with unilateral renovascular disease with a small kidney. In these groups of patients, we have tried to make the standard captopril renogram more objective by simultaneously estimating the individual kidney glomerular filtration rate (IKGFR). Twenty-five patients (10 bilateral, 15 unilateral) with angiographically proven renal artery stenosis (RAS) were studied. Ten renal units in five hypertensive patients with normal renal arteries were used as controls. A fall of more than 10% in IKGFR post-captopril was considered a positive result. The sensitivities of renogram and IKGFR in patients with bilateral RAS were 52.9% and 88.2% respectively. In patients with unilateral RAS, the sensitivities of renogram and IKGFR were 30% and 80% respectively. A significant fall in IKGFR was noted in eight of the 15 'normal' renal units of the unilateral RAS group. In conclusion, individual kidney GFR estimation in combination with captopril renography improved significantly the sensitivity in patients with symmetrical bilateral RAS and unilateral RAS with a small, poorly functioning kidney. A fall in GFR in the normal counterpart of a unilateral RAS kidney may be indicative of ongoing damage in the non-involved kidney.

The effect of balloon angioplasty on hypertension in atherosclerotic renal-artery stenosis. Dutch Renal Artery Stenosis Intervention Cooperative Study Group

BACKGROUND

Patients with hypertension and renal-artery stenosis are often treated with percutaneous transluminal renal angioplasty. However, the long-term effects of this procedure on blood pressure are not well understood.

METHODS

We randomly assigned 106 patients with hypertension who had atherosclerotic renal-artery stenosis (defined as a decrease in luminal diameter of 50 percent or more) and a serum creatinine concentration of 2.3 mg per deciliter (200 micromol per liter) or less to undergo percutaneous transluminal renal angioplasty or to receive drug therapy. To be included, patients also had to have a diastolic blood pressure of 95 mm Hg or higher despite treatment with two antihypertensive drugs or an increase of at least 0.2 mg per deciliter (20 micromol per liter) in the serum creatinine concentration during treatment with an angiotensin-converting-enzyme inhibitor. Blood pressure, doses of antihypertensive drugs, and renal function were assessed at 3 and 12 months, and patency of the renal artery was assessed at 12 months.

RESULTS

At base line, the mean (+/-SD) systolic and diastolic blood pressures were 179+/-25 and 104+/-10 mm Hg, respectively, in the angioplasty group and 180+/-23 and 103+/-8 mm Hg, respectively, in the drug-therapy group. At three months, the blood pressures were similar in the two groups (169+/-28 and 99+/-12 mm Hg, respectively, in the 56 patients in the angioplasty group and 176+/-31 and 101+/-14 mm Hg, respectively, in the 50 patients in the drug-therapy group; P=0.25 for the comparison of systolic pressure and P=0.36 for the comparison of diastolic pressure between the two groups); at the time, patients in the angioplasty group were taking 2.1+/-1.3 defined daily doses of medication and those in the drug-therapy group were taking 3.2+/-1.5 daily doses (P<0.001). In the drug-therapy group, 22 patients underwent balloon angioplasty after three months because of persistent hypertension despite treatment with three or more drugs or because of a deterioration in renal function. According to intention-to-treat analysis, at 12 months, there were no significant differences between the angioplasty and drug-therapy groups in systolic and diastolic blood pressures, daily drug doses, or renal function.

CONCLUSIONS

In the treatment of patients with hypertension and renal-artery stenosis, angioplasty has little advantage over antihypertensive-drug therapy.

Renal arterial stenosis: prospective comparison of color Doppler US and breath-hold, three-dimensional, dynamic, gadolinium-enhanced MR angiography

PURPOSE

To compare color Doppler ultrasonography (US) with fast, breath-hold, three-dimensional, gadolinium-enhanced magnetic resonance (MR) angiography in detecting renal arterial stenosis.

MATERIALS AND METHODS

Forty-five patients with clinical suspicion of renovascular disease were prospectively examined with intra- and extrarenal color Doppler US and breath-hold, gadolinium-enhanced MR angiography. Digital subtraction arteriography (DSA) was the standard of reference in all patients for the number of renal arteries and degree of stenosis.

RESULTS

DSA depicted 103 arteries and 52 stenoses. Color Doppler US was nondiagnostic in two examinations. Significantly more of 13 accessory renal arteries were detected with MR angiography (n = 12) than with color Doppler US (n = 3; P <.05). For assessing all stenoses, the sensitivity and accuracy were 94% and 91%, respectively, for MR angiography and 71% and 76%, respectively, for US (P <.05). The sensitivity was higher for MR angiography (100%) than for US (79%; P <.05) in diagnosing stenoses with at least 50% narrowing. The specificity, accuracy, and negative predictive value in diagnosing stenoses of at least 50% narrowing were 93%, 95%, and 100% for MR angiography and 93%, 89%, and 90% for US.

CONCLUSION

Breath-hold, gadolinium-enhanced MR angiography is superior to color Doppler US in accessory renal artery detection. Although the specificity of MR angiography is similar to that of color Doppler US, MR angiography has a better sensitivity and negative predictive value in depicting renal arterial stenoses.

Predicting the outcome of invasive treatment of renal artery disease

OBJECTIVE

Analysis of the factors influencing the outcome of performed or attempted invasive treatment for renal artery disease (RAD).

SETTING

University Hospital.

STUDY PATIENTS

Thirty-five hypertensive patients with 31 stenoses and 14 occlusions of renal artery.

INTERVENTIONS

Angioplasty was performed on 25 patients (attempted for 30), primary stenting on one, nephrectomy on three, and renal resection on one patient.

MAIN OUTCOME MEASURE

A decrease of diastolic blood pressure (DBP) by >/=15 mmHg after intervention.

RESULTS

A DBP response was seen in 24 patients. In 11 patients, invasive treatment did not result in a DBP response or failed technically. Compared with these patients, the responders were younger (55 +/- 11 vs. 66 +/- 8 years, P = 0.001) and tended to have higher DBP (100 +/- 8 vs. 93 +/- 11 mmHg, P = 0.065). The function of the affected kidney, or that of the more affected kidney if RAD was bilateral, was better preserved in responders (relative clearance on captopril renography 23 +/- 15 vs. 8 +/- 4%, P = 0.008). A response was more often seen in unilateral than in bilateral RAD (81% vs. 33%, P = 0.015). A relative clearance of </=10% on captopril renography had sensitivity of 88% and specificity of 81% for renal artery occlusion. Step-wise logistic analysis. (1) When DBP was< 95 mmHg with two antihypertensives, the response rate was 1/6 vs. 24/29 for more severe hypertension (P = 0.004). (2) Elderly patients had a response rate of 2/5 vs. 22/24 in younger patients (P = 0.024). (3) Response rates in bilateral and unilateral disease were not different, nor did the function of the affected kidney impact the DBP response. However, three of the four responders with </=10% relative clearance had an occluded renal artery and underwent nephrectomy.

CONCLUSIONS

Middle-aged patients with easily controlled hypertension and elderly hypertensives do not usually have a blood pressure response to the performed or attempted invasive treatment of RAD. Therefore, it seems recommendable not to screen such patients for RAD, unless their renal function is deteriorated. If the affected kidney functions poorly on captopril renography, angioplasty is usually not applicable and seldom leads to a blood pressure response.

Renovascular disease

The gold standard for the diagnosis of renal artery stenosis is angiography, with response to treatment the proof of its significance. Non-invasive methods of investigation are required and are now available including functional imaging, ultrasound, CT and MR angiography and the merits and limitations of these tests are discussed.

Atherosclerotic renal artery stenosis: from diagnosis to treatment

Renovascular hypertension represents a form of correctable hypertension and preventable renal failure. Such patients need to be identified early so that specific therapy can be instigated. Patient identification requires a high index of suspicion in patients with certain clinical features. Subsequent non-invasive imaging may result in angiography which is required for diagnostic purposes and for planning intervention. Correctable therapy takes one of two forms, namely percutaneous transluminal renal angioplasty, with or without stenting, or surgical revascularisation, together with modification of underlying risk factors.

Comparison of Tc-99m EC and Tc-99m DTPA captopril scintigraphy to diagnose renal artery stenosis

PURPOSE

Although, captopril scintigraphy is a well established method to detect renovascular hypertension, the optimal radiopharmaceutical for this test remains to be determined. Recently, Tc-99m ethylenedicysteine (Tc-99m EC) appeared as an alternative agent for captopril scintigraphy. The aim of this study was to compare the diagnostic accuracy of Tc-99m EC with Tc-99m DTPA, which is a well-established renal radiopharmaceutical for the captopril test.

METHODS

Nineteen hypertensive patients who had various degrees of renal artery stenosis on angiography were included in the study. All patients had baseline and captopril Tc-99m EC and Tc-99m DTPA scintigraphy within a 1-week period. The results were compared with angiography and in eight patients with changes in blood pressure after revascularization. The images were interpreted without knowledge of the angiography and revascularization data as low, intermediate, or high probability for hemodynamically significant renal artery stenosis, which was defined as an area of stenosis exceeding 50%.

RESULTS

Tc-99m EC and Tc-99m DTPA study results were in agreement in 16 of the 19 patients. In two patients with branch artery stenosis, Tc-99m EC was definitely superior to Tc-99m DTPA and correctly identified the probability of stenosis on scintigraphy. On kidney analysis, Tc-99m EC had a slightly greater diagnostic sensitivity compared with Tc-99m DTPA (79% vs. 68%; P > 0.05 by the chi-squared test) but equal specificity (93% for both agents). Both Tc-99m EC and Tc-99m DTPA showed the same accuracy in predicting the outcome after revascularization in all but one patient with branch artery stenosis, in whom Tc-99m EC accurately predicted a successful outcome of the intervention but Tc-99m DTPA did not. Tc-99m EC had better renal uptake in patients with decreased renal function and provided more dramatic evidence of renogram changes after captopril intervention, which resulted in more confident interpretation.

CONCLUSIONS

There is no significant difference between Tc-99m EC and Tc-99m DTPA captopril scintigraphy for detecting renal artery stenosis. However, because of the better imaging characteristics and more confident interpretation provided by the dramatic changes in the degree of renogram abnormality after captopril intervention, Tc-99m EC captopril scintigraphy should be used, particularly in patients with decreased renal function or branch artery stenosis.

Interventions in renal scintirenography

Nuclear nephrourology continues to develop and expand on traditional provocative physiological maneuvers, such as diuretic and captopril renography. In addition, newer interventions are conceived, such as aspirin renography, which test new and fascinating aspects of renal functional reserve. Since the last review of this topic in 1991, nephrourologic nuclear medicine has made considerable progress in diverse ways. Captopril and diuresis renography have made strides in establishing greater consensus of interpretation and procedure. Commonplace aspirin, the ubiquitous wonder drug, has revealed an unexpected role in renography by way of its inhibition of prostaglandin E2. Finally, further investigations of exercise renography in essential hypertension have deepened the plausibility of a renal role in the etiology of perhaps 50% of affected individuals.

Functional imaging of the kidneys with fast MRI techniques

Availability of faster and stronger gradient systems have given rise to a multitude of fast MRI data acquisition strategies which have tremendously increased the scope of MRI applications. These have led to the realization of long desired comprehensive approaches to evaluate anatomy and function using a single modality. In this work, we describe some of our own experiences with functional evaluation of the kidneys using MRI. Examples that suggest the feasibility of comprehensive approaches for evaluation of renal disease are also provided. We also introduce BOLD renal MRI, a method that may allow basic understanding of human renal physiology and pathophysiology in a way that has not been previously possible.

Screening for renovascular hypertension in a population with relatively low prevalence

OBJECTIVE

To evaluate the accuracy and cost-efficacy of the diagnostic procedure and treatment for renovascular hypertension.

SETTING AND PATIENTS

A total of 519 patients referred to the university clinic for hypertension were screened for renovascular hypertension with 405 captopril challenge tests (CCT) and 450 captopril renographies (CRG).

INTERVENTIONS

Abdominal angiography was performed on 84 patients for positive screening. Fifteen patients underwent angiography for a sole suspicious clinical presentation. The angiography revealed 17 renal artery stenoses and five occlusions in 20 patients. Fifteen technically successful angioplasties and three nephrectomies were performed.

RESULTS

In the patients who underwent angiography, CCT had a specificity of 39% and a sensitivity of 67% for renovascular hypertension. CRG had a sensitivity of 100% and a specificity of 68%. In the whole study population, the estimated specificity of CCT was 88% and that of CRG 95%. Invasive treatment reduced systolic/diastolic blood pressure from 157/99 to 140/87 mmHg and the number of antihypertensive drugs used from 2.6 to 1.4 in 16 patients (mean age 49 years). Angiotensin converting enzyme (ACE) inhibition was effective in four elderly patients. Cost-efficacy analysis Screening with CRG and invasive treatment cost US$15400 per successful invasive treatment Equally effective pharmacological treatment would have cost US$10400. Limiting the screening with CRG to the 173 patients with no obvious renal parenchymal disease and with hypertension at a younger age (< or =30 years) or unresponsive to two antihypertensive drugs (diastolic blood pressure > 90 mmHg) would have yielded a prevalence of 12% and missed only one elderly patient who responded to ACE inhibition. The limited screening, along with invasive treatment, would have cost US$7300 per patient

CONCLUSIONS

CRG is superior to CCT for screening of renovascular hypertension. Screening with CRG is cost-effective when limited to patients with no obvious renal parenchymal disease and with hypertension that does not respond to two antihypertensive drugs or is detected in patients no older than 30 years.