Optimization of single shot 3D breath-hold non-enhanced MR angiography of the renal arteries

BACKGROUND

Cardiac and navigator-gated, inversion-prepared non-enhanced magnetic resonance angiography techniques can accurately depict the renal arteries without the need for contrast administration. However, the scan time and effectiveness of navigator-gated techniques depend on the subject respiratory pattern, which at times results in excessively prolonged scan times or suboptimal image quality. A single-shot 3D magnetization-prepared steady-state free precession technique was implemented to allow the full extent of the renal arteries to be depicted within a single breath-hold.

METHODS

Technical optimization of the breath-hold technique was performed with fourteen healthy volunteers. An alternative magnetization preparation scheme was tested to maximize inflow signal. Quantitative and qualitative comparisons were made between the breath-hold technique and the clinically accepted navigator-gated technique in both volunteers and patients on a 1.5 T scanner.

RESULTS

The breath-hold technique provided an average of seven fold reduction in imaging time, without significant loss of image quality. Comparable single-to-noise and contrast-to-noise ratios of intra- and extra-renal arteries were found between the breath-hold and the navigator-gated techniques in volunteers. Furthermore, the breath-hold technique demonstrated good image quality for diagnostic purposes in a small number of patients in a pilot study.

CONCLUSIONS

The single-shot, breath-hold technique offers an alternative to navigator-gated methods for non-enhanced renal magnetic resonance angiography. The initial results suggest a potential supplementary clinical role for the breath-hold technique in the evaluation of suspected renal artery diseases.

Donors with renal artery stenosis: fit to donate

Kidney donation from hypertensive donors is now an accepted norm in live related kidney transplantation. The use of hypertensive donors with renal artery stenosis due to atherosclerosis and fibromuscular dysplasia is still debated. The prime concern is about the deleterious effect of hypertension on the donor and the risk of recurrence of such lesions in the solitary kidney. Even as the response of atherosclerotic renal artery stenosis to revascularisation is unpredictable, there is an improvement in blood pressure following revascularisation of kidneys with fibro-muscular dysplasia. The first use of such kidney donors was reported in 1984 and, since then, there have been a few reports of successful use of kidneys from donors with renal artery stenosis. We report here two interesting cases of successful transplantation of kidneys from live related kidney donors with hypertension due to renal artery stenosis who became normotensive with good graft function in the recipient. We conclude that moderately hypertensive donors with renal artery stenosis are fit to donate.

Pathogenesis and management of renovascular hypertension and ischemic nephropathy

Renovascular disease is an important cause of secondary hypertension and renal impairment. Atherosclerotic renal artery stenosis (ARAS) is the most important cause of renal artery stenosis (RAS), and has been linked to increased cardiovascular risk. The pathogenesis of renovascular hypertension is complex, but is mainly due to the over-activation of Renin-Angiotensin-Aldosterone system. A major consequence of untreated RAS is ischemic nephropathy, which is due to the sustained reduction in renal perfusion leading to derangement of microvascular function, and eventual development of interstitial fibrosis. Diagnosis of these conditions can be complex, sometimes needing invasive testing. Aggressive medical management is key to preventing progression of disease, as the role of revascularization in the management of ARAS is still not well defined.

Longitudinal changes in kidney parenchymal volume associated with renal artery stenting

OBJECTIVE

This study assessed the longitudinal changes in renal volume after renal artery stenting (RAS) to determine if renal mass is preserved by stenting.

METHODS

The study cohort consisted of 38 patients with longitudinal imaging available for renal volume quantification before and after RAS. Renal volume was estimated as (kidney length) × (width) × (depth/2) based on preoperative renal imaging. For each patient, the clinical response of blood pressure (BP) and renal function to RAS was categorized according to modified American Heart Association guidelines. Changes in renal volume were assessed using paired nonparametric analyses.

RESULTS

The cohort was a median age of 69 years (interquartile range [IQR], 60-74 years). A favorable BP response was observed in 11 of 38 patients (28.9%). At a median interval between imaging studies of 21 months (IQR, 13-32 months), ipsilateral renal volume was significantly increased from baseline (146.8 vs 133.8 cm(3);P = .02). This represents a 6.9% relative increase in ipsilateral kidney volume from baseline. A significant negative correlation between preoperative renal volume and the relative change in renal volume postoperatively (r = -0.42; P = .0055) suggests that smaller kidneys experienced the greatest gains in renal volume after stenting. It is noteworthy that the 25 patients with no change in BP or renal function-clinical failures using traditional definitions-experienced a 12% relative increase in ipsilateral renal volume after RAS. Multivariate analysis determined that stable or improved renal volume after stenting was an independent predictor of stable or improved long-term renal function (odds ratio, 0.008; 95% confidence interval, 0.000-0.206; P = .004).

CONCLUSIONS

These data lend credence to the belief that RAS preserves renal mass in some patients. This benefit of RAS even extends to those patients who would be considered treatment failures by traditional definitions. Patients with stable or increased renal volume after RAS had more stable renal function during long-term follow-up, whereas patients with renal volume loss after stenting were prone to deterioration of renal function.

Mid-aortic syndrome in a 3-year-old girl successfully treated by aorto-aortic grafting and renal artery implantation into the graft

Mid-aortic syndrome, an uncommon acquired or congenital condition characterized by segmental narrowing of the abdominal or distal descending thoracic aorta, is frequently accompanied by ostial stenosis of the aorta's branches. If left untreated, it can result in life-threatening complications secondary to severe hypertension.We report the case of a 3-year-old girl with congenital mid-aortic syndrome, who was diagnosed by chance in the course of a viral illness, and whose high blood pressure values were first dismissed as inaccurate. Attempts to achieve medical or endovascular control of her hypertension were unsuccessful. She was thereafter successfully treated by aorto-aortic bypass grafting, resection of the stenotic segments of both renal arteries, and implantation of the patent arterial segments into the graft.

Assessment of the kidneys: magnetic resonance angiography, perfusion and diffusion

Renal magnetic resonance (MR) imaging has undergone major improvements in the past several years. This review focuses on the technical basics and clinical applications of MR angiography (MRA) with the goal of enabling readers to acquire high-resolution, high quality renal artery MRA. The current role of contrast agents and their safe use in patients with renal impairment is discussed. In addition, an overview of promising techniques on the horizon for renal MR is provided. The clinical value and specific applications of renal MR are critically discussed.

Renal artery stenosis in kidney transplants: assessment of the risk factors

BACKGROUND

Transplant renal artery stenosis (TRAS) is an important cause of hypertension and renal allograft dysfunction occurring in kidney transplant recipients. However, conflicting predisposing risk factors for TRAS have been reported in the literature.

OBJECTIVE

The aim of the present study was to assess the potential correlation between possible risk factors and TRAS in a group of living donor renal transplant recipients 1 year after the renal transplantation.

METHODS

We evaluated the presence of renal artery stenosis in 16 recipients who presented with refractory hypertension and/or allograft dysfunction 1 year after renal transplantation. Screening for TRAS was made by magnetic resonance angiography and diagnosis was confirmed by conventional renal angiography. Age, gender, history of acute rejection, plasma lipid profile, serum creatinine, blood urea nitrogen, serum uric acid, calcium phosphate (CaPO₄) product, alkaline phosphatase, fasting blood sugar, hemoglobin, and albumin were compared between the TRAS and non-TRAS groups.

RESULTS

Of 16 kidney transplant recipients, TRAS was diagnosed in three patients (two men and one woman). High levels of calcium, phosphorous, CaPO₄ product, and low-density lipoprotein (LDL) cholesterol were significantly correlated with the risk of TRAS 1 year after renal transplantation (P < 0.05). Serum level of uric acid tended to have a significant correlation (P = 0.051).

CONCLUSION

Correlation between high CaPO₄ product, LDL cholesterol, and perhaps uric acid and TRAS in living donor renal transplant recipients 1 year after renal transplantation might suggest the importance of early detection and tight control of these potential risk factors.

Noninvasive In vivo assessment of renal tissue elasticity during graded renal ischemia using MR elastography

OBJECTIVES

: Magnetic resonance elastography (MRE) allows noninvasive assessment of tissue stiffness in vivo. Renal arterial stenosis (RAS), a narrowing of the renal artery, promotes irreversible tissue fibrosis that threatens kidney viability and may elevate tissue stiffness. However, kidney stiffness may also be affected by hemodynamic factors. This study tested the hypothesis that renal blood flow (RBF) is an important determinant of renal stiffness as measured by MRE.

MATERIAL AND METHODS

: In 6 anesthetized pigs MRE studies were performed to determine cortical and medullary elasticity during acute graded decreases in RBF (by 20%, 40%, 60%, 80%, and 100% of baseline) achieved by a vascular occluder. Three sham-operated swine served as time control. Additional pigs were studied with MRE 6 weeks after induction of chronic unilateral RAS (n = 6) or control (n = 3). Kidney fibrosis was subsequently evaluated histologically by trichrome staining.

RESULTS

: During acute RAS the stenotic cortex stiffness decreased (from 7.4 ± 0.3 to 4.8 ± 0.6 kPa, P = 0.02 vs. baseline) as RBF decreased. Furthermore, in pigs with chronic RAS (80% ± 5.4% stenosis) in which RBF was decreased by 60% ± 14% compared with controls, cortical stiffness was not significantly different from normal (7.4 ± 0.3 vs. 7.6 ± 0.3 kPa, P = 0.3), despite histologic evidence of renal tissue fibrosis.

CONCLUSION

: Hemodynamic variables modulate kidney stiffness measured by MRE and may mask the presence of fibrosis. These results suggest that kidney turgor should be considered during interpretation of elasticity assessments.

Renovascular hypertension: screening and modern management

The diagnosis and management of patients with renovascular disease and hypertension continue to elude healthcare providers. The advent of novel imaging and interventional techniques, and increased understanding of the pathways leading to irreversible renal injury and renovascular hypertension, have ushered in commendable attempts to optimize and fine-tune strategies to preserve or restore renal function and control blood pressure. Large randomized clinical trials that compare different forms of therapy, and smaller trials that test novel experimental treatments, will hopefully help formulate innovative concepts and tools to manage the patient population with atherosclerotic renovascular disease.

Atherosclerotic renal artery stenosis--diagnosis and treatment

Renal artery stenosis (RAS) is characterized by a heterogeneous group of pathophysiologic entities, of which fibromuscular dysplasia and atherosclerotic RAS (ARAS) are the most common. Whether and which patients should undergo revascularization for ARAS is controversial. The general consensus is that all patients with ARAS should receive intensive medical treatment. The latest randomized clinical trials have increased confusion regarding recommendations for revascularization for ARAS. Although revascularization is not indicated in all patients with ARAS, experts agree that it should be considered in some patients, especially those with unstable angina, unexplained pulmonary edema, and hemodynamically significant ARAS with either worsening renal function or with difficult to control hypertension. A search of the literature was performed using PubMed and entering the search terms renal artery stenosis, atherosclerotic renal artery stenosis, and renal artery stenosis AND hypertension to retrieve the most recent publications on diagnosis and treatment of ARAS. In this review, we analyze the pathways related to hypertension in ARAS, the optimal invasive and noninvasive modalities for evaluating the renal arteries, and the available therapies for ARAS and assess future tools and algorithms that may prove useful in evaluating patients for renal revascularization therapy.

[Indications for balloon angioplasty of the renal arteries: to revisit?]

Presentation in several international conferences, at the stage of design and interim results of randomized trials regarding the appropriateness of percutaneous endovascular correction of renal artery stenosis has raised some questions among clinicians, including nephrologists. What lessons should get the interventional radiologist now published the first results?

[Endovascular treatment for renal artery stenosis]

Atherosclerosis accounts for 90% of the cases of renal artery stenosis. It is an important cause of secondary arterial hypertension by means of inducing the renin-angiotensin system, volume expansion, and sympathetic activation. Despite high procedural success rate of renal artery stenting, clinical trials have shown an inconsistent outcome about improvement in hypertension. The accurate predictors identify the good indication for renal artery stenting is clinically needed. Currently, the presence of hemodynamically critical stenosis causing renal ischemia, the presence of symptoms with undoubtedly benefit from revascularization, and the assessment of procedural risk are key factors for decision making about indication of renal artery stenting.

[Auscultation of the abdomen]

Normal bowel sounds vary considerably in intensity, pitch and frequency. Due to the wide range of physiological variation, the clinical significance of abdominal bowel sounds is limited. There is no clear evidence that very high-pitched bowel sounds have clinical pertinence. Small bowel obstruction is more commonly associated with hyperactive bowel sounds than with substantially diminished or absent bowel sounds. In 4-20% of young adults, systolic bruits are heard in the epigastric region that are not associated with abnormalities. There is no evidence that abdominal aortic aneurysms are associated with abdominal bruits. An abdominal bruit is indicative of renal artery stenosis when blood pressure control remains unsatisfactory, in particular when the bruit is also heard during diastole.

Atherosclerotic renovascular hypertension: current trends in diagnosis and management

Reno vascular hypertension (RVH) is an important challenge for clinicians managing patients with hypertension. With recent advances in imaging techniques, the diagnosis and recognition of Renal artery stenosis (RAS) has increased resulting in a 3-4 fold increase in endovascular procedures. Recent prospective, randomized trials have demonstrated equivocal results for interventions and a third trial is under way. In managing such patients, clinicians need to consider the risk-benefit of expensive and invasive workup and interventions.

[Unstable hypertension due to renal artery compression by the developed diaphragm in a 17-year-old athlete: a case report]

A 17-year-old high school boy was admitted to our hospital because of hypertension. Doppler ultrasound of the renal arteries and 3D-CT angiography showed a stenosis of the right renal artery, which was pushed against the aorta by the right crus of the diaphragm. He underwent aortography and selective renal arteriography. His right renal artery originated from the aorta at a higher level than the left renal artery, between the celiac artery and the superior mesenteric artery. Renal arteriography confirmed a 50% reduction in diameter (stenosis) of the proximal right renal artery entrapped by the right diaphragmatic crus. This pathology, unlike common renal artery stenosis, sometimes requires surgical decompression or an aortorenal bypass graft, because renal angioplasty with stenting is reported to be at risk of complication by a fracture of the stent. However, the patient rejected surgical decompression for fear of deterioration of his athletic ability. Therefore we decided to follow up his blood pressure and renal size by ultrasound every six months. Renovascular hypertension caused by diaphragmatic entrapment is a very rare disease. The diagnosis may be overlooked easily at angiography if optimal views are not obtained. It is important to display images of the renal arteries, the celiac artery and the superior mesenteric artery in both inspiration and expiration.

Diagnosis of secondary hypertension: an age-based approach

Secondary hypertension is a type of hypertension with an underlying, potentially correctable cause. A secondary etiology may be suggested by symptoms (e.g., flushing and sweating suggestive of pheochromocytoma), examina- tion findings (e.g., a renal bruit suggestive of renal artery stenosis), or laboratory abnormalities (e.g., hypokalemia suggestive of aldosteronism). Secondary hypertension also should be considered in patients with resistant hyper- tension, and early or late onset of hypertension. The prevalence of secondary hypertension and the most common etiologies vary by age group. Approximately 5 to 10 percent of adults with hypertension have a secondary cause. In young adults, particu- larly women, renal artery stenosis caused by fibromuscular dyspla- sia is one of the most common secondary etiologies. Fibromuscular dysplasia can be detected by abdominal magnetic resonance imag- ing or computed tomography. These same imaging modalities can be used to detect atherosclerotic renal artery stenosis, a major cause of secondary hypertension in older adults. In middle-aged adults, aldosteronism is the most common secondary cause of hyperten- sion, and the recommended initial diagnostic test is an aldosterone/ renin ratio. Up to 85 percent of children with hypertension have an identifiable cause, most often renal parenchymal disease. Therefore, all children with confirmed hypertension should have an evaluation for an underlying etiology that includes renal ultrasonography.

Magnetic resonance angiography and Doppler scanning for detecting atherosclerotic renal artery stenosis

BACKGROUND

Atherosclerotic renal artery stenosis (ARAS) is a progressive but potentially reversible chronic kidney disease. Although the high sensitivity and specificity of renal Doppler scanning (RDS) for ARAS has been reported in western countries, ARAS has not been detected by RDS. This study used magnetic resonance angiography (MRA) to evaluate the sensitivity and specificity of RDS for detecting ARAS among outpatients at a nephrology clinic, and to calculate the degree of underestimation of ARAS by RDS.

METHODS

A total of 257 outpatients, aged > 50 years were examined for ARAS by RDS and MRA.

RESULTS

Thirty-seven (14.4%) and 139 (54.1%) of 257 patients had stenosis detected by RDS and MRA, respectively. Among the 220 patients whose RDS results were negative, MRA detected stenosis in 111 (50.45%). Multivariate logistic regression analysis showed that age > 65 years, duration of smoking, coronary artery disease, and serum creatinine levels > 354 mmol/L (4 mg/dL) were significant and independent factors that influenced ARAS in patients with negative results by RDS.

CONCLUSION

RDS might still be the diagnostic procedure of choice for screening outpatients for ARAS because it is inexpensive, convenient, able to detect severity, and avoids the use of contrast media. When RDS is negative in aged people who have smoked longer than 20 years, with coronary artery disease or serum creatinine > 4 mg/dL, MRA is recommended for further evaluation of ARAS.