Renal scintigraphic captopril test in the diagnosis of renovascular hypertension

Assessment of angiotensin-converting enzyme inhibitor/angiotensin receptor blocker on the split renal function in the patients with primary hypertension

Bilateral kidney damage in hypertensive patients is not parallel. Angiotensin-converting enzyme inhibitor/angiotensin receptor blocker (ACEI/ARB), as a commonly used antihypertensive drug, could protect kidney function and delay its deterioration. Most studies focused on overall renal function, but the researches on split renal function (SRF) are rare. We investigated the effects of ACEI/ARB on the SRF in patients with primary hypertension.Patients with primary hypertension (n = 429; male: 213; female: 216) admitted to our department between January 2014 and December 2016 were included in this study. The glomerular filtration rate (GFR) of split and total renal function were determined using diethylenetriaminepentaacetic acid tagged with 99mTc renal dynamic imaging method. For the same patient, the side with high GFR was considered as higher GFR kidney, whereas that with a low GFR was considered as lower GFR kidney. The split function score (Q value) was utilized to evaluate the differences of bilateral renal function. The patients were divided into 3 groups based on the Q values (Group 1, Q value <5%; Group 2, Q value of 5%-10%; Group 3, Q value ≥10%). All the patients received antihypertensive therapy based on ACEI/ARB. The renal dynamic imaging was performed in the 1-year follow-up to investigate the changes of the SRF.Compared with the baseline level, significant decline was noticed in the serum creatinine (Scr) in Group 2 and Group 3 (P < .05). The cystatin C in Group 3 showed significant decline (P < .05). Compared with the baseline, there was significant decline in the Q value in Group 2, whereas the GFR of lower GFR kidney showed significant increase (P < .05). No statistical differences were noticed in the Q value and split GFR in Group 1 and Group 3 (P > .05).In primary hypertension patients, ACEI/ARB therapy could improve the SRF of lower GFR kidney in the presence of certain differences between the SRF. As a result, the SRF difference was reduced. In case of Q value in a range of 5% to 10%, ACEI/ARB could improve the renal function effectively. It may be significant for the design of antihypertensive drugs.

Nuclear imaging in the genitourinary tract: recent advances and future directions

For almost three decades, noninvasive radionuclide procedures for the evaluation of renal disease have been important components of nuclear medicine practice. With the introduction of new imaging agents and procedures, these techniques can provide valuable data on perfusion and function of individual kidneys. In general, these procedures are easy to perform and carry a low radiation burden and sedation is not required. Moreover, radionuclide imaging of the genitourinary tract has become an invaluable asset to clinicians in the evaluation of renal parenchyma and urologic abnormalities.

Non-surgical treatment of patients with peripheral vascular disease

Dotter first described percutaneous revascularization of peripheral vascular disease (PVD) in 1964. In 1974, Gruentzig developed a balloon catheter for dilation of vascular lesions. Currently, percutaneous transluminal angioplasty (PTA) employs a variety of devices ranging from implantable stents to endovascular radiation devices for re-stenosis and is recognized as a safe and effective alternative to surgery for selected patients. In addition to the general efficacy of peripheral angioplasty, which is comparable to that of bypass surgery for selected lesions, angioplasty offers several distinct advantages over surgery. It is performed under local anaesthesia, making it feasible to treat patients who are at high risk for general anaesthesia. When compared to surgical revascularization, the morbidity from angioplasty is low, generally related to problems at the vascular access site, and mortality is extremely rare. Unlike vascular surgery, there is no recovery period after angioplasty, and most patients can return to normal activity within 24-48 h of an uncomplicated procedure. Finally, angioplasty can be repeated if necessary usually without increased difficulty or increased patient risk compared to the first procedure, and does not preclude surgery as adjunctive or definitive therapy.

Renal angioplasty: better for treating hypertension or for rescuing renal function?

Angioplasty of renal artery stenosis has been used extensively in the last two decades for treating renovascular hypertension, and, more recently, for preserving the jeopardized renal function. A large body of evidence has accumulated indicating that this approach is by far the most convenient for patients with fibromuscular stenosis in whom the technical success of the procedure is followed by a high cure rate (50%) or at least by some improvement of blood pressure (40%). In contrast, in patients with atheromatous stenosis, the rate of cure is very low (8-10% at best) and the rate of improvement is between 40 and 50% irrespective of whether the stenosis is treated with angioplasty or with stent implantation. Thus, before undergoing procedures which are not devoid of potentially serious side-effects, these patients should be thoroughly investigated to select those in whom the benefit actually outweighs the risks. Studies investigating the effects of angioplasty on renal function are less numerous than those addressing the effects on blood pressure, and, in most cases, suffer the limitation of using the levels of serum creatinine as the sole marker of the changes in glomerular filtration rate induced by the procedure. These investigations have shown that some amelioration can be achieved in one-third of patients, with another third having unmodified levels of creatinine at follow-up. Radioisotopic techniques, which allow a more precise and separate evaluation of the function of the two kidneys, appear to be a promising alternative for the investigation of the effects of angioplasty; indeed, preliminary studies which took advantage of these methodologies have shown that the function of the stenotic kidney can possibly be rescued by slowly reversing the multiple mechanisms by which chronic ischaemia damages the kidney.

Risk of morbidity from renovascular disease in elderly patients with congestive cardiac failure

BACKGROUND

Renovasular disease commonly affects elderly people. Elderly patients with heart failure are routinely treated with angiotensin-converting-enzyme (ACE) inhibitors, which may increase risk of renal dysfunction. We investigated the frequency of renovascular disease among elderly people with heart failure.

METHODS

From the local population of Salford, UK, we recruited 86 patients with heart failure with a mean age of 77.5 (SD 5.6) years, who were admitted as acute emergencies or who attended general medical clinics. We selected patients by intention to treat with ACE inhibitors. We used captopril renography to screen for renovascular disease. All patients with abnormal renograms underwent magnetic-resonance angiography of the renal arteries as well as 40% of patients with normal renograms as negative controls.

FINDINGS

Magnetic-resonance angiography showed severe renovascular disease (>50% renal-artery stenosis or occlusion) in 29 (34%) patients. Captopril renography had an estimated sensitivity of 78.8% (95% CI 72.7-97.8) and specificity of 94.3% (67.6-97.3) for detection of renovascular disease. The estimated positive predictive value of captopril renography was 89.7% and the negative predictive value was 87.5%. Patients with renovascular disease had worse renal function (mean creatinine 201 [SD 56] vs 136 [40] pmol/L, p<0.001), were older (mean age 80.7 [5.6] vs 76.8 [5.3] years, p<0.01), and were more likely than patients without renovascular disease to have peripheral arterial disease.

INTERPRETATION

Some elderly patients with occult renovascular disease on ACE inhibitors will be at risk of developing uraemia. Renal function should be closely monitored to detect any deterioration early.

Can the IVIM model be used for renal perfusion imaging?

OBJECTIVE

Renal perfusion imaging may provide information about the hemodynamic significance of a renal artery stenosis and could improve noninvasive characterization when combined with angiography. It was proposed previously that diffusion sequences could provide useful perfusion indices based on the intravoxel incoherent motion (IVIM) model. Owing to motion artifacts, diffusion imaging has been restricted to relatively immobile organs like the brain. With the availability of single-shot echo-planar imaging (EPI) our purpose was to evaluate the IVIM model in renal perfusion.

METHODS AND MATERIAL

Eight volunteers underwent diffusion-sensitive magnetic resonance (MR) imaging of the kidneys using a spin echo (SE) EPI sequence. The diffusion coefficients determined by a linear regression analysis and fits to the IVIM function were calculated.

RESULTS AND CONCLUSION

Our preliminary experience does not support the possibility of obtaining perfusion information using the IVIM model in the kidneys.

Renal arterial disease and hypertension

Renal artery stenoses can cause hypertension and renal failure. These lesions can be relatively easily diagnosed and most can be successfully treated. Recognizing them is important because relief of stenoses either by angioplasty or surgical revascularization often cures the hypertension and, if renal failure is present, improves or stabilizes excretory function.

Distal vessel atherosclerosis as a cause for false-positive renal scintigraphy

While captopril-enhanced renal scintigraphy is acknowledged to be a useful screening technique to detect clinically silent obstructive lesions of the main renal arteries, the presence of significant atherosclerosis of distal, smaller renal vessels as a cause of positive scintigraphy scans has not been reported extensively. In a retrospective 2-year analysis of 31 consecutive captopril-enhanced renal scintigrams, we found a total of 13 studies in 11 patients that were classified as "positive" for renal artery stenosis. Of these 11 patients with positive scintigraphic studies, 4 patients underwent 5 renal arteriography procedures; only 1 of these renal arteriograms showed significant stenosis of the main renal artery. In the other 4 cases, an angiographic pattern of diffuse intrarenal distal arterial disease correlated with scintigram lateralization. Angiography was also performed in 4 patients with negative captopril renal scintiscans. In each of these cases the arteriogram was also negative for significant renal artery stenosis, and only 1 patient had diffuse bilateral intrarenal arterial disease. We conclude that distal renal arterial narrowing should be considered in the differential diagnosis of lateralized renal scintigrams. A negative renal scintigraphic study may be more reliable for excluding significant main renal artery obstructive disease.

Secondary hypertension: evaluation and treatment

Most patients with hypertension in the United States have essential (primary) hypertension (95%), the cause of which is unknown. The remaining 5% of adults with hypertension have the secondary form of hypertension, the cause and pathophysiologic process of which are known. Internists and other primary care physicians refer to this as treatable or curable hypertension, because the hypertension can be managed or even controlled with medications. Similarly, the condition is called surgical hypertension by surgeons in the belief that once the cause is determined and identified, surgical intervention will result in cure of hypertension. Secondary causes of hypertension include renal parenchymal disease, renovascular diseases, coarctation of the aorta, Cushing's syndrome, primary hyperaldosteronism, pheochromocytoma, hyperthyroidism, and hyperparathyroidism. Occasionally included in this category are alcohol- and oral contraceptive-induced hypertension and hypothyroidism, but these conditions are not discussed herein. The evaluation of secondary hypertension is of interest and can bring together different facets of anatomy, physiology, pharmacology, and radiology in the medical and surgical treatment of these disorders. Despite enthusiasm that can be generated in the evaluation of these conditions, evaluation can be expensive and should not be conducted for all patients with hypertension. Features that aid in the diagnosis of secondary hypertension include the following: 1. Onset of hypertension before the age of 20 or after the age of 50 years. The presence of hypertension at a young age may suggest coarctation of the aorta, fibromuscular dysplasia, or an endocrine disorder. Hypertension found for the first time after the age of 50 years may suggest the presence of renovascular hypertension caused by atherosclerosis. 2. Markedly elevated blood pressure or hypertension with severe end-organ damage, as in grade III or IV retinopathy. These findings suggest the presence of renovascular hypertension or pheochromocytoma. 3. Specific body habitus and ancillary physical findings. For example, truncal obesity and purple striae occur with hypercortisolism, and exophthalmos is associated with hyperthyroidism. 4. Resistant or refractory hypertension (poor response to medical therapy usually necessitating use of more than three antihypertensive medications from three different classes). 5. Specific biochemical test that suggest the existence of certain disorders, such as hypercalcemia in hyperparathyroidism, hyperglycemia in Cushing's syndrome and pheochromocytoma, and unprovoked hypokalemia with renin-producing tumors, primary hyperaldosteronism, or renin-mediated renovascular hypertension. 6. Other characteristics that may suggest secondary hypertension such as abdominal diastolic bruits (renovascular hypertension), decreased femoral pulses (coarctation of the aorta), or bitemporal hemianopias (Cushing's disease). A combination of a good history and physical examination, astute observation, and accurate interpretation of available data usually are helpful in the diagnosis of a specific causation.

Renal nuclear medicine

The measurement of renal function has been a major field of interest in nuclear medicine. Many studies in the literature are still dedicated to this subject, with the aim of replacing the traditional urinary clearance methods with simpler and easier techniques. Simplified plasma clearance methods appear of sufficient accuracy to estimate global kidney function, except in very low function in which urinary clearance is still indicated. Gamma-camera methods have also been developed that, although of a lesser accuracy than the in vitro techniques, offer the important advantage of allowing renal imaging with the estimation of separate kidney function. Because of the intimate link between kidney function and structure, the diagnosis of nephrourological diseases has represented an important goal of nuclear medicine research. The functional information attainable with radionuclides is a valuable complement to the morphological information of imaging techniques such as x-ray computed tomography, ultrasonography, and magnetic resonance imaging. Recent contributions of nuclear medicine to the progress of clinical nephrology include the evaluation of renal function and the diagnostic work-up of renovascular hypertension, obstructive nephropathy, urinary tract infection, and renal transplantation.

The value of captopril renal scintigraphy in assessing the results of percutaneous transluminal renal angioplasty and in following up renovascular hypertension--a case report

Percutaneous transluminal renal angioplasty (PTRA) was performed in a patient with bilateral renal artery stenoses diagnosed noninvasively by captopril renal scintigraphy and confirmed by renal arteriography. The captopril renal scintigraphy parameters returned to normal in correlation with improved blood pressure response fifteen days after PTRA. Five months later hypertension reappeared and the repeated captopril renal scintigraphy suggested left renal artery stenosis. PTRA was repeated and a stent was implanted with reversal of blood pressure, and captopril renal scintigraphy findings returned to normal levels. Six months after second PTRA, the blood pressure increased to hypertensive levels, and captopril renal scintigraphy indicated left renal artery stenosis. The renal arteriography, however, revealed a new stenosis at the left renal artery ostium. The PTRA with a second stent implantation was performed successfully. The captopril renal scintigraphic parameters and the blood pressure were again normalized after the last intervention and remained normal for thirteen months of follow-up.

Nuclear medicine evaluation of hypertension

Noninvasive diagnosis of renovascular hypertension using nuclear medicine techniques has evolved in the past 30 years through improvements in imaging equipment, radiotracers, and, most recently, captopril intervention. Characteristic patterns of normal and abnormal renograms using typical radiotracers are demonstrated, including renal artery stenosis. Comparison with other tests, both invasive and noninvasive, are made with the aim toward identifying anatomic as well as physiologic definitions of renovascular hypertension. Pitfalls in the methodology are also described. The main advantage of captopril renography is enhancement of the sensitivity, and particularly the specificity, of the radionuclide diagnosis of renovascular hypertension. Available investigations have identified captopril renography as the likely procedure of choice in the noninvasive identification of renovascular hypertension.

Technetium-99m diethylene triamine penta-acetic acid and dimercaptosuccinic acid in the detection of a segmental branch stenosis of the renal artery by captopril renography

We present a case in which a 39-year-old woman with correctable bilateral renovascular hypertension did not show abnormality during post-captopril technetium-99m dimercaptosuccinic acid (DMSA) study. Post-captopril 99mTc-diethylene triamine penta-acetic acid (DTPA) scintigraphy revealed the adverse effect of a stenosis of the artery supplying the upper part of her left kidney but failed to uncover the existence of severe multiple narrowings of the right renal artery. After bilateral renovascular reconstructive surgery, the hypertension completely disappeared. This case illustrates that DTPA may be more efficacious than DMSA in the detection of segmental loss of renal function induced by angiotensin converting enzyme inhibition.

Suppression of renal vein renin profiles by mannitol prophylaxis: implications in the evaluation of renovascular hypertension

Renal arteriography with concomitant renal vein renin profiling remains the diagnostic standard for evaluating the anatomic and physiologic significance of stenotic renal artery lesions in hypertensive patients. False-negative renal vein renin profiles with failure of lateralization in patients with anatomically apparent high-grade stenosis complicate the diagnostic process. Mannitol is frequently administered prophylactically to minimize the risk of dye nephropathy in these patients. Yet, the potential effects of mannitol on renal vein renin profiling in man have not been previously reported. Seven patients with renovascular hypertension were studied prospectively to determine changes in renal vein renin profiles before and after mannitol prophylaxis. Despite captopril stimulation, all patients demonstrated significant renin suppression leading to the loss of renin lateralization in patients with unilateral renovascular hypertension. In 60% of the patients, renal vein renin ratios fell to below the standard 1.5 to 1 ratio after mannitol infusion. In patients with bilateral renovascular disease, the least stenotic side suppressed completely, while the more stenotic side suppressed partially. Percent suppression analysis showed a mean suppression of 56.8% on the stenotic side versus 8.2% on the noninvolved side (P less than 0.002). In every study, suppression equaled or exceeded 32% on the involved side and was less than this on the noninvolved side. Thus, the degree of renin suppression following mannitol infusion may prove to be an important tool in the diagnosis of clinically significant stenotic lesions. The mechanism of mannitol-induced suppression remains undefined, but appears independent of volume expansions or dilutional effects. The inhibitory effects of mannitol on renin profiles can obscure the diagnosis of underlying renovascular hypertension.

Diagnostic usefulness of renal scanning after angiotensin converting enzyme inhibitors

Radioisotopic renal scanning after angiotensin converting enzyme inhibition (ACEI) has proven to be an exciting area for research. The biologic activity of markers such as DTPA and hippuran, when combined with the physiological effects of ACEI, may provide noninvasive methods of diagnosing both renal artery stenosis and renovascular hypertension. Recent investigators have demonstrated that the sensitivities and specificities of these tests may vary widely; these differences are probably due to variations in study design, patient population, diagnostic criteria, and outcome measurements. We have reviewed these studies and discuss these possible sources of variation and their impact on the clinical usefulness of these diagnostic tests, especially in relation to the prevalence of disease in the population. Current results suggest that the post-ACEI DTPA scan is relatively accurate in the diagnosis of renal artery stenosis, with sensitivity generally greater than 90% and specificity around 95%. However, the best results in predicting the response to angioplasty or surgery in patients with renal artery stenosis have been with the use of post-ACEI hippuran in combination with furosemide (sensitivity, 96%; specificity, 95%). With confirmation of these findings and continued investigation, it is expected that accurate noninvasive tests will be available for widespread clinical use in the near future.

Simplified captopril renography in diagnosis and treatment of renal artery stenosis

To improve the diagnosis and forecast the response to surgery or renal angioplasty in patients with hypertension and renal artery stenosis, we employed a simplified captopril renography protocol in conjunction with renal arteriography in 94 clinically selected patients. Fifty hypertensive patients (group 1) with a high clinical likelihood of renovascular hypertension were evaluated using a simplified captopril renography protocol and renal angiography on the arterial side. Criteria for normal captopril renal scintigrams were established based on this original cohort and validated in an additional 44 clinically comparable patients (group 2). Renal revascularization or nephrectomy was performed in 39 patients, and success of the procedure was determined in the 34 patients for whom 3-month follow-up was available. In the 94 patients, 44 (47%) had renal artery stenosis. Simplified captopril renography was 91% sensitive and 94% specific in identifying or excluding renal artery stenosis in the combined group, with no difference in the diagnostic utility between groups 1 and 2, or in those with renal insufficiency (n = 38) or those with bilateral disease (n = 17). Scintigraphic abnormalities induced by captopril were strongly associated with cure or improvement in blood pressure control following revascularization or nephrectomy (15 of 18), while the lack of captopril-induced changes was associated with failure of such intervention (13 of 16) (p = 0.0004). We conclude that simplified captopril renography is highly sensitive and specific in the diagnosis of renal artery stenosis in a clinically selected high-risk population and that the test accurately predicts the success or failure of therapeutic intervention.

Renal artery imaging: a prospective comparison of intra-arterial digital subtraction angiography with conventional angiography

This study describes a systematic comparison of intra-arterial digital subtraction angiography (DSA) of the main renal arteries with conventional angiography (CA), the currently accepted "gold standard" for the diagnosis of renal artery stenosis. Twenty-five patients scheduled for abdominal aortography for various indications underwent first DSA then CA. The DSA and CA images were evaluated for number of renal arteries, presence and grade of renal artery stenosis, presence of post-stenotic dilation or fibromuscular changes, and diagnostic and pictorial adequacy of the images. DSA was found to be diagnostically adequate in 92% of cases, compared with 96% for CA. In evaluating significant main renal artery stenosis, which the authors assumed to be any stenosis greater than 50%, there were 10 such stenoses seen by CA. DSA also detected 10 cases, but there was 1 false positive and 1 false negative, yielding a sensitivity of 90% and a specificity of 98%. There was also close correlation of DSA and CA for the few cases of post-stenotic dilatation and fibromuscular dysplasia encountered. The authors conclude that DSA is an acceptable substitute for CA in the evaluation of patients for main renal artery stenosis.

Interventions in renal scintigraphy

Physiological and pharmacological intervention for the purpose of determining organ functional reserve is a familiar concept in medical testing and in nuclear medicine. Nephrourologic applications include established procedures such as diuretic scintigraphy for determination of urinary outflow obstruction and captopril scintigraphy for determination of renovascular hypertension. Subtle renal dysfunction may exist among some individuals with essential hypertension, induced by provocative exercise renography, and not observed at rest. The strength of nuclear medicine resides in its ability to assess disorders of organ function for the diagnostic, prognostic, or pathophysiological information provided. Nephrourologic interventions are reviewed with an emphasis on the functional changes caused by the intervention.

Furosemide-131I-hippuran renography after angiotensin-converting enzyme inhibition for the diagnosis of renovascular hypertension

PURPOSE

We have previously demonstrated the greater sensitivity of 131I-hippuran renography than 99mTC-DTPA scintigraphy to diagnose renovascular hypertension (RVH). This study assesses the predictive diagnostic value of furosemide-131I-hippuran renography after angiotensin-converting enzyme (ACE) inhibition in patients with and without RVH.

PATIENTS AND METHODS

All patients were investigated at the University of Miami/Jackson Memorial Medical Center. Twenty-eight patients had RVH and 22 did not. Twenty-eight patients had normal or minimally decreased renal function (serum creatinine level 1.5 mg/dL or less) and 22 had renal insufficiency (serum creatinine level 1.8 mg/dL or more). Renography was performed 60 minutes after oral administration of 50 mg captopril or 10 minutes after intravenous injection of 40 micrograms/kg enalaprilat. Forty milligrams of furosemide were administered intravenously 2 minutes after injection of 131I-hippuran. The residual cortical activity (RCA) of 131I-hippuran was measured at 20 minutes.

RESULTS

RVH was unlikely when RCA after ACE inhibition was less than 30% of peak cortical activity. Conversely, RVH was present when 131I-hippuran cortical activity steadily increased throughout the test to reach 100% at 20 minutes. In azotemic patients with RCA between 31% and 100%, RVH was differentiated from intrinsic renal disease by obtaining a baseline renogram without ACE inhibition and comparing RCA in that study and RCA after ACE inhibition. If RCA increased (indicating worsening renal function) after ACE inhibition, RVH was likely; whereas, intrinsic renal disease was more likely if RCA remained unchanged or decreased (indicating improved renal function) with ACE inhibition. The test had a specificity of 95% and a sensitivity of 96% in this population. There was a direct correlation between the results of angioplasty or surgery on high blood pressure and the changes in RCA before and after intervention (n = 20).

CONCLUSION

Furosemide-131I-hippuran renography with ACE inhibition is highly predictive in identifying patients with RVH.

Inadequacy of captopril challenge test for diagnosing renovascular hypertension in children and adolescents

A captopril challenge test (CCT) for renovascular disease in adults was described recently. We used it in 20 consecutive, untreated hypertensive children and adolescents. All had a normal urinalysis and glomerular filtration rate and non-diagnostic renal sonograms or intravenous urograms. Plasma renin activity (PRA) was measured before and 1 h after administration of captopril (0.76 +/- 0.17 mg/kg). The CCT was positive in 10 patients. Renal arteriograms were performed in 7 patients with a positive CCT and in 2 with a negative CCT. Renovascular disease was found in 4 patients, 1 of whom had a negative CCT. The PRA response to captopril was the same in patients with true- and the false-positive tests. The predictive value of the positive test was 43%. In conclusion, we did not find the CCT, as described for adults, to be of value in children and adolescents.

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

PURPOSE

The purpose of this study was to determine the sensitivity, specificity, and clinical usefulness of renography performed in combination with captopril administration ("captopril renography") in diagnosing renal artery stenosis.

PATIENTS AND METHODS

Fifty-five patients with suspected renal artery stenosis underwent renography prior to performance of renal angiography. Renography was performed on two consecutive days using technetium-99m-diethylenetiamine pentaacetic acid (DTPA) as an index of glomerular filtration rate and iodine-131-orthoiodohippurate (OIH) as an index of renal blood flow. Captopril (25 mg orally, crushed) was administered 1 hour before the second study. Renal artery stenosis was defined as a stenosis exceeding 70%. Renographic criteria were then established, retrospectively, to differentiate renal artery stenosis from essential hypertension based on (1) asymmetry of function and (2) the presence of captopril-induced changes.

RESULTS

Renal artery stenosis was detected in 35 of 55 patients (21 with unilateral and 14 with bilateral stenosis). Three criteria were established for diagnosing renal artery stenosis: (1) a percent uptake of DTPA by the affected kidney of less than 40% of the combined bilateral uptake, (2) a delayed time to peak uptake of DTPA, which was more than 5 minutes longer in the affected kidney than in the contralateral kidney, (3) a delayed excretion of DTPA, with retention at 15 minutes, as a fraction of peak activity, more than 20% greater than in the contralateral kidney. The presence of one or more of these criteria was diagnostic of renal artery stenosis, with a sensitivity and specificity of 71% and 75%, respectively before captopril administration, and 94% and 95% after captopril administration. Lesser degrees of asymmetry (i.e., uptake of 40% to 50%) had very poor diagnostic specificity. Among patients with bilateral stenoses, asymmetry identified the more severely affected kidney, but the presence or absence of stenosis in the contralateral kidney could not be reliably determined. When pre- and post-captopril studies were compared, the presence of captopril-induced scintigraphic changes was a highly specific finding for renal artery stenosis, but occurred in only 51% of the cases. OIH scintigraphy provided similar results, with slightly lower sensitivity and specificity.

CONCLUSION

Asymmetry of DTPA uptake, time to peak uptake, or retention seen on a single post-captopril renogram is a highly sensitive and specific finding in detecting renal artery stenosis but does not distinguish unilateral from bilateral disease. If renograms are obtained both before and after captopril administration, the presence of captopril-induced change is a highly specific finding for the detection of renal artery stenosis, but the sensitivity of this finding is low.

[Status of the captopril test in the diagnosis of hypertension]

The place of captopril (C) testing in the screening for renovascular hypertension is still controversial. Baseline and C-stimulated plasma renin concentrations (PRC) were measured in 113 hypertensives, who where referred for the exclusion of secondary hypertension. In addition intravenous digital subtraction angiography (DSA) and a renal scintigraphy were performed. When renal artery disease was revealed by DSA or renin was stimulated the renal arteries were visualized by direct arteriography (and treated by angioplasty if possible). 86 patients underwent each diagnostic test: 21% had renovascular hypertension. Unilateral renal artery stenosis (n = 10) was detected by the captopril test (cutoff values: baseline greater than 40 microU/ml, after C greater than 180 microU/ml, sensitivity 100%). Bilateral renal artery stenosis (n = 8) was missed when the disease was equally severe on either side (sensitivity 50%). The specificity of C testing was 82%, overall sensitivity (uni- and bilateral disease 78%, prevalence 21%, predictive value of the positive test 0.56, predictive value of the negative test 0.93). With i.v.-DSA the renal arteries were technically evaluable in 91% (82/92) of cases. The sensitivity for the detection of all renal artery stenoses was 79% (uni-lateral 100%, bilateral 40%, specificity 97%). The sensitivity of renal scintigraphy for the detection of unilateral renal artery stenoses was 50%, for the detection of bilateral renal artery stenoses 43%, specificity 81%. The present study demonstrates the usefulness of captopril for the detection of unilateral renal artery stenosis.(ABSTRACT TRUNCATED AT 250 WORDS)

The diagnostic dilemma: a clinician's viewpoint

The prevalence of renovascular hypertension appears to be increasing, particularly in older patients with generalized arteriosclerosis, hypertension and impaired renal function. While clinical clues remain extremely useful in identifying patients at increased risk, older screening tests have been largely abandoned in favor of angiographic methods that provide visual identification of renal artery lesions. Renal scintigraphic techniques, with or without angiotensin-converting enzyme (ACE) inhibition, offer the potential for providing accurate measurements of renal function, and may be particularly useful in identifying critical renal arterial stenosis. In assessing the future role of scintigraphy, careful clinical validation of these correlations will be necessary, as will determinations of their usefulness in patients with renal insufficiency and those with bilateral renal artery stenosis. The role of adrenal scintigraphy in the localization of adrenal tumors is also reviewed. Their cost-effectiveness, limitations in sensitivity and specificity compared to current diagnostic technologies, and potential applications are discussed.

Differential diagnosis and management of renovascular hypertension through nuclear medicine techniques

Identification of patients with renovascular hypertension (RVH) among the larger group of patients with essential hypertension has been aided by a wide variety of in vitro and in vivo nuclear medicine procedures. The most valuable in vitro procedure remains the radioimmunoassay (RIA) for renin activity obtained from individual renal vein catheterization studies. Lateralizing renin activity provides valuable prognostic information about the likelihood for surgical cure of RVH. Older in vivo procedures for the diagnosis of RVH included rectilinear scanning and probe renography, which suffered from poor resolution and specificity, respectively. These tests have been replaced by computer-interfaced gamma camera scintirenography using 131I- or 123I-labeled orthoiodohippurate (OIH), or scintiangiography using 99mTc-DTPA. False-positive (FP) results for RVH persist due to a wide variety of relatively common conditions that can cause asymmetric renal size and function, including outflow obstruction and parenchymal renal disease. Newer approaches promise to improve the specificity of nuclear medicine procedures for identification of RVH. In particular, the number of FP exams appears to improve when scintirenography is performed before and after the administration of oral angiotensin converting enzyme (ACE) inhibitors, using either 99mTc-DTPA or OIH. The incentive for improved diagnostic testing has increased with the availability of percutaneous transluminal angioplasty (PCTA) for treatment of renal artery stenosis (RAS). Follow up of PCTA with scintirenography is of great value in assessing its effect on renal function and in evaluating the subsequent clinical course of the patient.

Renovascular hypertension: etiology and pathophysiology

Evidence from animal studies demonstrates that the renin-angiotensin (ANG II) system and sodium retention play major roles in experimental renovascular hypertension (RVH). Two basic models have been described. In the first, one-clip two-kidney Goldblatt hypertension, the ischemic kidney secretes renin, which leads to increased ANG II formation and hence elevation of blood pressure (BP). As BP rises, sodium excretion by the intact contralateral kidney increases (pressure natriuresis); therefore, there is no sodium retention. In the second, one-clip one-kidney Goldblatt hypertension, the contralateral kidney is removed. In this case the pressure natriuresis can no longer occur, and sodium retention occurs. The ensuing expansion of plasma volume inhibits renin secretion, so that in this model the renin level is normal or low. Following the clipping of the renal artery, renal blood flow and pressure are maintained distal to the stenosis by an ANG II-mediated vasoconstriction. This acts preferentially on the efferent glomerular arterioles, so that the ratio of preglomerular to postglomerular resistance is reduced, which helps to maintain glomerular filtration despite the reduced renal perfusion pressure. In the contralateral kidney the afferent arteriolar resistance is increased, probably as a direct result of exposure to the higher intrarenal arterial pressure. ANG II constricts the efferent arterioles in the same way as in the ischemic kidney, so that the ratio of preglomerular to postglomerular resistance is unchanged. When an angiotensin converting enzyme (ACE) inhibitor is given, the efferent arterioles vasodilate. In the ischemic kidney this may produce a reduction of glomerular filtration rate (GFR), which is not seen in the contralateral kidney. Unilateral RVH in humans corresponds closely to the animal model of one-clip two-kidney hypertension. Plasma renin activity is usually high, and converting enzyme inhibitors lower BP effectively. The increased renin is due exclusively to increased secretion of renin by the ischemic kidney, and is completely suppressed in the contralateral kidney. It is not clear whether bilateral RVH corresponds to the one-clip one-kidney model, but there is circumstantial evidence to suggest that both renin and volume factors may be involved. The majority of cases of human RVH are caused by atheroma, which is commonly bilateral, or by fibromuscular dysplasia. The former tends to be associated with atheroma elsewhere in the arterial tree, and often progresses to complete occlusion and renal failure. The latter occurs in younger patients, and almost never progresses to complete occlusion.

Abnormal glomerular and tubular function during angiotensin converting enzyme inhibition in renovascular hypertension evaluated by the lithium clearance method

Glomerular filtration rate (GFR) and tubular function were measured by means of the lithium clearance technique in 14 patients with renovascular hypertension (RVH) and eight patients with essential hypertension (EH) before and after oral administration of captopril 25 mg. In RVH captopril reduced 51-Cr-EDTA clearance (67.3 (median) to 47.5 ml min-1, P less than 0.01), proximal absolute reabsorption of fluid (53.9 to 41.5 ml min-1, P less than 0.01) and distal absolute reabsorption of sodium (2195 to 1402 mumol min-1, P less than 0.01), whereas proximal fractional reabsorption increased slightly (77.5 to 80.2%, P less than 0.02). In EH, however, these parameters were practically unaffected by captopril. In both RVH and EH plasma concentrations of angiotensin II and aldosterone were reduced after captopril, but atrial natriuretic peptide in plasma and urinary excretion rate of prostaglandin E2 were unchanged. Blood pressure decreased after captopril in both groups, but the maximum fall in systolic BP was more pronounced in RVH (22%) than EH (13%). It is concluded that angiotensin converting enzyme inhibition markedly reduced absolute reabsorption in both the proximal and distal tubules in RVH, in contrast to EH, predominantly due to fall in the GFR, and that the slight increase in proximal fractional reabsorption may be attributed to a reduction in the hydrostatic pressure in the peritubular vessels.

Renal artery duplex ultrasonography: a reliable new screening test for functionally significant renal artery stenosis

1. Renal artery duplex ultrasonography (RADU) has recently become available as a rapid, relatively inexpensive, non-invasive screening test for renal artery stenosis causing renovascular hypertension. 2. We compared the sensitivity of RADU with that of computerized nuclear renography (CNR) in 16 patients with renovascular hypertension. All had lateralizing renal venous renin ratio (RVRR) studies, 15 had renal artery stenosis (RAS) on angiography and one had unilateral chronic parenchymal renal disease (CPRD). 3. We found RADU to be at least as reliable as CNR with sensitivities of 100% and 93.7%, respectively. Neither RADU nor CNR was successful (sensitivity 25% and 0%, respectively) in detecting minor, functionally insignificant contralateral renal artery stenosis in four patients, two of whom had multiple small renal arteries--a recognized difficulty in the use of RADU. 4. After successful (RVRR became negative) therapeutic intervention in two patients with RAS (dilatation one, surgery one), RADU changed from positive to negative and may therefore be a useful alternative to repeat angiography in this setting. 5. Performed in conjunction with renal parenchymal B mode ultrasound, RADU correctly identified the presence of CPRD in one patient.