Differing patterns of renal vein renin secretion in patients with renovascular hypertension, and their role in predicting the response to angioplasty

An Interventionist's Guide to Endocrine Consultations

Endocrinopathies are a heterogeneous group of disorders often resulting from pathologic sources of hormone production. When the clinical scenario, laboratory testing, and noninvasive imaging fail to aid confident identification of the source of hormone excess, endocrine venous sampling may localize obscure lesions to guide subsequent treatment. Knowledge of basic hormone signaling pathways, common pathophysiologic disruptions of these pathways, and serologic evaluation fosters informed conversations with referring physicians and effective patient selection. Success in the angiography suite requires familiarity with normal and variant anatomy of the multiple organs of the endocrine system, patient preparation, stimulation and sampling techniques, specimen handling, and results interpretation. ^©RSNA, 2017.

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.

Urine Attenuation Ratio: A New CT Indicator of Renal Artery Stenosis

OBJECTIVE

The purpose of our study was to evaluate the value of a ratio of the attenuation measurements of urine in each kidney (hereafter referred to as the urine CT attenuation ratio) in the detection and lateralization of significant renal artery stenosis (RAS).

SUBJECTS AND METHODS

In 33 patients with suspected renovascular hypertension and 43 normotensive patients, 5-mm-thick transverse CT scans of the kidney area were obtained 4 min after helical CT angiography (CTA). The attenuation of urine in each kidney was measured, and its ratio was calculated. All 76 patients underwent intraarterial digital subtraction angiography within 2 days after the CT examination. The results of angiography were correlated with the urine attenuation ratio of both kidneys.

RESULTS

Twenty-six patients showed significant RAS: unilaterally in 20 and bilaterally in six patients. Two patients showed moderate stenosis of renal arteries. The other patients with essential hypertension (n = 5) or normal blood pressure (n = 43) showed normal renal arteries. The CT attenuation of urine in each kidney was measured and its ratio calculated in all patients except four patients with unilateral RAS. The urine CT attenuation ratio in 22 patients with significant RAS ranged from 1.11 to 4.76 (mean, 2.07). The two patients with moderate RAS showed ratios of 1.83 and 1.23. The others (n = 48) had a urine CT attenuation ratio that ranged from 1.00 to 1.54 (mean, 1.07). The difference of the ratio between the RAS group and the normal group was statistically significant (p < 0.01). The mean urine CT attenuation ratio was 2.18 in patients with unilateral RAS (n = 16) and 1.75 in patients with bilateral RAS (n = 6). The difference of the ratio between the two groups was not statistically significant (p = 0.16). At a cutoff value of 1.22, the sensitivity, specificity, positive predictive value, and negative predictive value of the urine CT attenuation ratio in the diagnosis of significant RAS were 95%, 96%, 91%, and 98%, respectively.

CONCLUSION

The urine CT attenuation ratio is a simple and reliable indicator with which to detect and lateralize significant RAS and is a useful adjunct to helical CTA.

Cardiovascular disease in neurofibromatosis 1: report of the NF1 Cardiovascular Task Force

PURPOSE

Patients with neurofibromatosis 1 (NF1) are at increased risk for a variety of cardiovascular disorders, but the natural history and pathogenesis of these abnormalities are poorly understood.

METHODS

The National Neurofibromatosis Foundation convened an expert task force to review current knowledge about cardiovascular manifestations of NF1 and to make recommendations regarding clinical management and research priorities related to these features of the disease.

RESULTS

This report summarizes the NF1 Cardiovascular Task Force's current understanding of vasculopathy, hypertension, and congenital heart defects that occur in association with NF1. Recommendations are made regarding routine surveillance for cardiovascular disease and diagnostic evaluation and management of cardiovascular disorders in individuals with NF1.

CONCLUSION

Our understanding of the natural history and pathogenesis of cardiovascular disease in NF1 has improved substantially in the past few years, but many clinically important questions remain unanswered.

Renal vein renin measurements accurately identify renovascular hypertension caused by total occlusion of the renal artery

OBJECTIVE

To assess the usefulness of indexes derived from renal vein renin measurements.

DESIGN

A 12-year prospective study.

SETTING

A tertiary institutional referral centre.

PATIENTS AND METHODS

Between 1988 and 2000, we studied 152 consecutive hypertensive patients with a high pre-test probability of renovascular hypertension (RVH). RVH was diagnosed retrospectively on the basis of reduction in blood pressure after correction of ischaemia at follow-up. Renal vein renin measurements were used to calculate the ratios: Visch/Vctl (renal vein renin ratio; RVRR); Vctl/Viivc; (Visch - Viivc)/Viivc; (Vctl - Viivc)/Viivc, where Visch and Vctl indicate plasma renin activity (PRA) in the ischaemic and contralateral renal veins, respectively, and Viivc denotes PRA in the infrarenal inferior vena cava. A receiver operator characteristics (ROC) curve analysis was used to determine the cut-off value of renal vein renin measurement indexes that provided the best discrimination between patients with and without RVH and to identify patients with RVH caused by total occlusion of the renal artery.

RESULTS

Sixty-seven patients were diagnosed as having RVH: 51 had significant renal artery stenoses (RVH non-occluded) and 16 had total renal artery occlusion (RVH occluded). Of the remaining 85 patients in whom RVH was excluded (non-RVH group), 27 had reno-parenchymal hypertension and 58 had essential hypertension. Of the renal vein renin measurement indexes, only RVRR and (Visch - Viivc)/Viivc in RVH-occluded patients differed significantly (P < 0.005) from those in the non-RVH group and showed the best performance by ROC curve analysis. This analysis also showed that, at any cut-off value, RVRR was far more accurate for identification of RVH-occluded patients than for identification of RVH non-occluded patients, both in the subgroup with unilateral and, even more so, in those with bilateral renal artery lesions. The best trade-off between sensitivity and false-positive rate was provided by cut-off values of 1.55 and 1.70 of the RVRR for identification of non-occluded and occluded RVH, respectively.

CONCLUSIONS

RVRR is more useful for establishing an indication for nephrectomy in patients with renal artery occlusion than for identifying those patients with renal artery stenosis who will benefit from revascularization. In patients with RVH with bilateral renal artery lesions, lateralization of renin secretion occurs only in the presence of total renal artery occlusion. Different cut-off values are necessary for identification of non-occluded and occluded RVH.

Hypertension and renovascular disease: follow-up on 100 renal vein renin samplings

The clinical value of renal vein renin sampling (RVRS) as a prognostic tool in the treatment of renovascular hypertension was evaluated. One hundred consecutive patients were included over a 4-year period of time. About half of the patients (49%) were treated interventionally by PTRA (21%), nephrectomy (20%), or vascular surgery (8%). Seven patients (15%) were cured and 15 (32%) had improved (reduction in antihypertensive medicine) after 6 months follow-up, whereas three patients (6%) were cured and 12 (26%) improved after 3-4 years follow-up. Thus, the number of patients cured or improved is comparable with the results from our department reported 20 years ago. However, in the present report, more than twice as many patients were enrolled, leading to double costs. Different indices of lateralisation of the renin generation were calculated for the use in cases of a shrunken kidney (functional share < or =15%). None of the indices clearly discriminated between the patients who did benefit from intervention, and those who did not. The only positive finding was that a peripheral renin concentration lower than 8 mlU/l predicted no effect of intervention, which might lead to the exclusion of 11% of the patients before entering the diagnostic programme. We conclude that the RVRS demands a very restrictive referral pattern if it should be of prognostic value for the blood pressure outcome after intervention. No indices of lateralised renin concentrations proved high predictive value. However, a peripheral renin concentration low in the normal range seems useful as an indicator of no benefit from intervention.

Computed tomography-derived intrarenal blood flow in renovascular and essential hypertension

The effect of renal artery stenosis on intrarenal perfusion and volume in renovascular hypertensive patients is unclear. Alterations in these attributes may ultimately be involved in deterioration of renal function. We measured whole kidney, cortical, and medullary perfusion and volume with electron beam computed tomography (EBCT) in 33 hypertensive patients, with well-preserved renal function, scheduled for renal angiography. EBCT-derived whole kidney perfusion was lower in patients with atherosclerotic renal artery stenosis (RAS; N = 20) than in fibromuscular dysplasia (FMD; N = 10) or essential hypertension (N = 28; P < 0.05), as was cortical perfusion (2.44 +/- 0.16 vs. 3.26 +/- 0.17 and 3.07 +/- 0.09 ml/min/cc tissue, respectively, P < 0.005), but medullary perfusion was similar. Whole kidney, cortical, and medullary perfusion correlated inversely with degree of stenosis in FMD, but not in atherosclerotic RAS. Renal volumes were similar. These results demonstrate that, in contrast to patients with FMD, in patients with atherosclerotic RAS the decrease in cortical perfusion is not directly related to the degree of stenosis in the main renal artery. Factors other than the stenosis itself may play a role in the pathophysiology of atherosclerotic RAS and associated renal failure.

Acute blockage of the renin system and differential renal vein renin determinations in the diagnosis of renovascular hypertension

For validation of differential renal vein renin determinations in the diagnosis of renovascular hypertension (RVH), we investigated 102 patients suspected of suffering from RVH before and 1 h after administration of 25 mg captopril. Sensitivity, specificity and posterior probability for renin ratio (RR) and renin secretion (RS) were calculated based on 44 patients with proven RVH and 58 patients with primary hypertension (PH) using discriminant analysis. There is good (> 95%) and identical specificity of both variables under all conditions, whereas sensitivity remains poor even after Captopril administration (RR 23% vs. 32%; RS 20% vs. 34%). The posterior probabilities obtained by discriminant analysis revealed a cut-off point of 2.5 for the renin ratio and of 1.9 for the renin secretion. No change is observed after ACE inhibition. We conclude that the acute blockade of the renin system by captopril in differential renin sampling yields no advantages in diagnosing RVH and that there is no difference between RR and RS in the diagnosis of RVH.

Renal vein renin analysis: limitations of its use in predicting benefit from percutaneous angioplasty

Two hundred forty-four consecutive patients (mean age 61 years), including 123 who had technically valid renal vein renin (RVR) analysis and 121 without RVR data, underwent technically successful percutaneous renal artery angioplasty (PTRA). They were retrospectively examined to evaluate the utility of RVR analysis in identifying renal hypertension (RVH), predicting benefit from PTRA, and determining if the lack of knowledge of renin levels significantly affected clinical outcome after PTRA. Abnormal RVR values were associated wtih clinical benefit after PTRA in 62 of 93 patients (67% sensitivity, 20% specificity, 72% positive predictive value). Clinical improvement following PTRA occurred in 31 of 37 patients with normal pre-PTRA RVR values (16% negative predictive value). RVR analysis correctly identified 86 of 117 patients with renovascular hypertension (74% sensitivity, 16% negative predictive value). Improved blood pressure (BP) control occurred in 72% with abnormal RVR analysis and 66% of the 121 patients without RVR data (p > 0.1). We conclude that the very low negative predictive value significantly limited the use of RVR analysis in this elderly (mean age 60 years) patient population with a high incidence of mild renal functional impairment (mean serum creatinine 1.4 mg/dl) and bilateral renal artery stenosis (38%). The lack of pre-PTRA renin data did not significantly affect clinical outcome. If RVR data were relied upon as the exclusive selection criterion in patients of this type, many would be prevented from having the benefit of cure or improvement by PTRA.

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.

The angiographic incidence of renal artery stenosis in the arteriosclerotic population

The incidence of renal artery stenosis was evaluated with intra-arterial digital subtraction angiography in 100 consecutive patients referred for peripheral arteriopathy. Fifty-seven patients were normotensive, 43 were hypertensive. In the normotensive group, renal artery stenosis was found in ten patients (17.5%). In the hypertensive group renal artery stenosis was found in twelve patients (28%). It is concluded that the incidence of renal artery stenosis is high in an arteriosclerotic population both in normotensive and hypertensive patients.

Long-term prognosis of surgical treatment of renovascular hypertension

During the period 1974-1986, 71 patients were operated on for renovascular hypertension. Forty-eight patients had atherosclerotic disease and 23 patients had fibromuscular dysplasia. There was no operative mortality. Fourteen patients died during the follow-up, 12 of them from cardiovascular causes. The 57 surviving patients were reexamined with a mean follow-up of 7 years. The relative cumulative 5- and 10-year survival rates in all patients were 79% and 55%, respectively. At follow-up, seven (19%) of the atherosclerotic patients were classified as cured, 22 (59%) as improved and eight (22%) as failures. In the patients with fibromuscular dysplasia, 12 (60%) were normotensive without medication, and six (30%) were improved. The relative 5-year survival rates in these aetiological groups were 73% and 90%, respectively. Only complete cure of hypertension by surgery predicted a good outcome, whereas very similar survival curves were found in the improved and failed groups. This could be due to a higher incidence of target organ changes before surgery in the latter groups. A positive blood pressure response to long-term converting-enzyme inhibition correlated well with the response to surgery. Renal venous renin studies correctly predicted long-term outcome of surgery in 78% of the patients studied, but require careful preparation of the patients and interpretation of results.

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.

Radiologic diagnosis of renovascular hypertension and percutaneous transluminal renal angioplasty

Percutaneous transluminal renal angioplasty (PTRA) is a low risk, cost-effective procedure with a high degree of technical and therapeutic success in most categories of renovascular hypertension (RVH) when performed at experienced centers. The role of radiology in screening and diagnosis is discussed with special attention to renal vein sampling for renin assay (RVR) and digital subtraction angiography (DSA). The results of PTRA are compared with surgery. At New York Hospital, PTRA is the procedure of first choice in fibromuscular dysplasia, unilateral nonostial atheroma, arteritis, renal transplantation, and pediatrics. In patients with bilateral and ostial atherosclerotic disease and/or azotemia, the choice between surgery or PTRA depends on the surgical risk category of the patient.