Residency · Residency · Vascular Surgery
Renal Artery Disease: Renovascular Hypertension and Ischemic Nephropathy
Overview
Renal artery stenosis (RAS) is an important cause of secondary hypertension and can lead to progressive renal insufficiency. The two primary underlying pathologies are atherosclerotic RAS, which accounts for approximately 90% of cases, and fibromuscular dysplasia (FMD), responsible for about 10%. Although renal artery revascularization was once a common treatment approach, its role has been significantly limited by landmark negative clinical trials such as ASTRAL and CORAL. Current clinical practice emphasizes identifying the small subset of patients who may truly benefit from revascularization.
Atherosclerotic Renal Artery Stenosis
Epidemiology
Atherosclerotic RAS affects between 1% and 5% of hypertensive patients and is found in up to 40% of individuals undergoing cardiac catheterization. The stenosis typically involves the ostium and the proximal 1 to 2 centimeters of the renal artery, reflecting spillover from aortic plaque. Bilateral involvement occurs in 30% to 50% of cases. This condition is strongly associated with widespread atherosclerotic disease, including coronary artery disease, cerebrovascular disease, and peripheral arterial disease. There is a male predominance in its occurrence.
Pathophysiology
Renovascular hypertension arises due to reduced renal perfusion pressure, which activates the renin-angiotensin-aldosterone system (RAAS). In unilateral RAS, the affected kidney retains sodium, while the contralateral kidney initially compensates through pressure natriuresis. However, in bilateral RAS or when stenosis affects a solitary kidney, the hypertension becomes volume-dependent because there is no contralateral kidney to compensate. Chronic hypoperfusion in ischemic nephropathy leads to tubular atrophy, interstitial fibrosis, glomerulosclerosis, and progressive loss of renal parenchyma, manifesting as cortical thinning. These changes become irreversible if the ischemia is longstanding.
Clinical Features Suggestive of Renovascular Hypertension
Certain clinical features raise suspicion for renovascular hypertension. These include the onset of hypertension before age 30 or after age 55, accelerating or refractory hypertension resistant to three or more antihypertensive agents, hypertension accompanied by unexplained renal insufficiency, and hypertension with asymmetric kidney size exceeding 1.5 cm difference. Flash pulmonary edema is a hallmark of bilateral RAS or RAS affecting a solitary kidney. Acute kidney injury following initiation of an ACE inhibitor or ARB suggests critical bilateral RAS or solitary kidney involvement. An abdominal bruit may also be present on physical examination.
<image>Diagram illustrating the pathophysiology of renovascular hypertension showing the renin-angiotensin-aldosterone system activation in response to renal artery stenosis, with differentiation between unilateral RAS (renin-dependent) and bilateral RAS (volume-dependent) mechanisms</image>
Diagnosis
Duplex ultrasound is the first-line screening modality for RAS. A peak systolic velocity (PSV) greater than 200 cm/s or a renal-to-aortic ratio (RAR) exceeding 3.5 suggests at least 60% stenosis. A resistive index (RI) above 0.8 indicates intrarenal disease, which correlates with a poor response to revascularization. Kidney size asymmetry and the presence of a tardus-parvus waveform in segmental arteries further support the diagnosis. Computed tomography angiography (CTA) provides excellent anatomic detail and is considered the gold standard for procedural planning, demonstrating ostial calcified plaques, stenosis severity, and renal parenchymal volume. However, CTA carries a risk of contrast nephropathy in patients with chronic kidney disease. Magnetic resonance angiography (MRA) is an alternative for patients with renal insufficiency, with non-contrast techniques available. MRA may overestimate stenosis severity, and gadolinium contrast is contraindicated if the estimated glomerular filtration rate (eGFR) is below 30 due to the risk of nephrogenic systemic fibrosis. Catheter angiography remains the definitive diagnostic test and can be combined with pressure gradient measurements; a translesional systolic gradient greater than 20 mmHg indicates hemodynamic significance. This invasive procedure is typically reserved for patients in whom intervention is planned.
| Feature | Atherosclerotic RAS | Fibromuscular Dysplasia |
|---|---|---|
| Prevalence | ~90% of RAS | ~10% of RAS |
| Demographics | Older; male predominance; atherosclerotic risk factors | Young to middle-aged women (80–90%) |
| Location | Ostium and proximal 1–2 cm | Mid-to-distal renal artery |
| Angiographic appearance | Focal ostial stenosis with calcified plaque | "String of beads" (medial fibroplasia) |
| Bilateral | 30–50% | 35–60% |
| Treatment | Medical therapy (CORAL/ASTRAL); revascularize only for flash pulmonary edema, refractory HTN, or declining renal function | Balloon angioplasty (cure/improvement in 60–80%) |
| Long-term patency of intervention | Stent: variable; open bypass >90% at 5 yr | PTA: 90–95% technical success; rarely needs stent |
Fibromuscular Dysplasia (FMD)
Features
Fibromuscular dysplasia is a non-atherosclerotic, non-inflammatory arterial disease that predominantly affects young to middle-aged women, accounting for 80% to 90% of cases. The most common subtype is medial fibroplasia, seen in over 80% of patients, which produces a characteristic "string of beads" appearance on angiography. FMD typically involves the mid-to-distal segments of the renal artery and spares the ostium. Bilateral disease occurs in 35% to 60% of cases. FMD often affects multiple vascular beds, including the carotid, vertebral, iliac, and mesenteric arteries, and is associated with arterial aneurysms, dissections, and intracranial aneurysms.
Treatment of FMD-Related RAS
Percutaneous balloon angioplasty is the treatment of choice for medial fibroplasia and yields excellent results, with technical success rates of 90% to 95% and hypertension cure or improvement in 60% to 80% of patients. Stenting is rarely necessary and is reserved for complications such as dissection or vessel recoil. Although no randomized trials exist, strong observational evidence supports this approach. Medical management with antihypertensive agents is used as needed. Given the systemic nature of FMD, screening for associated lesions, particularly carotid FMD and intracranial aneurysms, is recommended, with brain MRA being the preferred modality.
Landmark Trials for Atherosclerotic RAS
ASTRAL Trial (2009)
The ASTRAL trial randomized 806 patients with atherosclerotic RAS to receive either revascularization with stenting plus medical therapy or medical therapy alone. The study found no significant difference between groups in renal function, blood pressure control, cardiovascular events, or mortality. However, the trial faced criticism for enrolling patients with mild to moderate stenosis and potential selection bias, as patients with clear indications for intervention were excluded.
CORAL Trial (2014)
The CORAL trial enrolled 947 patients with atherosclerotic RAS of at least 60% stenosis and randomized them to stenting plus medical therapy versus medical therapy alone. This well-conducted trial demonstrated no benefit of stenting in terms of the composite cardiovascular and renal endpoint, blood pressure control, or renal function. The results have largely curtailed the routine use of renal artery stenting.
Implications
For the majority of patients with atherosclerotic RAS, optimal medical therapy suffices. This includes the use of ACE inhibitors or ARBs if tolerated, statins, antiplatelet agents, and careful blood pressure control. Revascularization does not improve outcomes in most patients with atherosclerotic RAS.
<image>Forest plot or summary graphic of the CORAL trial primary endpoint results showing no significant benefit of renal artery stenting plus medical therapy versus medical therapy alone for the composite of cardiovascular and renal events, annotated with key subgroup findings</image>
Current Indications for Renal Artery Revascularization
Atherosclerotic RAS (Highly Selective)
Revascularization is reserved for highly selected patients. The strongest indication is flash pulmonary edema occurring in the context of bilateral RAS or RAS to a solitary kidney. Other indications include refractory hypertension despite maximal medical therapy with three or more drugs including a diuretic, progressive renal insufficiency attributable to RAS (manifested as declining eGFR with bilateral disease or solitary kidney), unstable angina in patients with bilateral RAS who cannot tolerate ACE inhibitors or ARBs, and rapidly declining renal function after starting ACE inhibitors or ARBs, which suggests critical bilateral RAS.
Technique for Renal Artery Stenting
Renal artery stenting is typically performed via femoral or brachial arterial access. For ostial lesions, a balloon-expandable stent is placed, protruding 1 to 2 millimeters into the aorta to ensure adequate coverage. Embolic protection devices may reduce the risk of atheroembolic renal injury, although data supporting their use are limited. Technical success rates exceed 95%.
Open Surgical Options
Open surgical approaches include aortorenal bypass using saphenous vein or prosthetic grafts from the aorta to the renal artery, renal artery endarterectomy via a transaortic approach, and extra-anatomic bypasses such as hepatorenal or splenorenal bypass that avoid aortic clamping. These options are generally reserved for patients undergoing concurrent aortic surgery, those with failed stenting, or those with complex anatomy. Surgical procedures have excellent patency rates exceeding 90% at five years but carry higher perioperative risks.
Clinical Pearls
Most patients with atherosclerotic RAS are best managed with optimal medical therapy, as clearly demonstrated by the CORAL and ASTRAL trials. Flash pulmonary edema in the setting of bilateral RAS remains the strongest indication for revascularization; this clinical scenario was underrepresented in the negative trials. Fibromuscular dysplasia is a distinct disease from atherosclerotic RAS, and balloon angioplasty is highly effective for medial fibroplasia. It is important to assess the resistive index on duplex ultrasound; an RI greater than 0.8 suggests intrarenal parenchymal disease unlikely to improve with revascularization. ACE inhibitors and ARBs can be safely used in unilateral RAS with close monitoring of creatinine but are dangerous in bilateral RAS or RAS affecting a solitary kidney. When FMD is diagnosed in the renal arteries, screening for involvement of other vascular beds, especially carotid, vertebral, and intracranial arteries, is essential. Finally, a kidney size less than 7 cm or cortical thickness under 1 cm suggests irreversible ischemic nephropathy, making revascularization unlikely to recover renal function.
References
- Cooper CJ, et al. Stenting and medical therapy for atherosclerotic renal-artery stenosis (CORAL trial). N Engl J Med. 2014;370(1):13-22.
- ASTRAL Investigators. Revascularization versus medical therapy for renal-artery stenosis (ASTRAL trial). N Engl J Med. 2009;361(20):1953-1962.
- Olin JW, et al. Fibromuscular dysplasia: state of the science. Circulation. 2014;129(9):1048-1078.
- Herrmann J, Lerman A. Atherosclerotic renal artery stenosis: current evidence and future directions. Am J Kidney Dis. 2007;49(4):527-539.
- Caps MT, et al. Prospective study of atherosclerotic disease progression in the renal artery. Circulation. 1998;98(25):2866-2872.
