OVERVIEW

What is renal artery stenosis?

In daily life, water pipes can rust and accumulate deposits over time, causing the inner diameter to narrow and water supply to decrease. The renal artery is like the water supply pipe for the kidneys. When the renal artery becomes diseased, leading to kidney ischemia and increased blood pressure, renal artery stenosis occurs. Renal artery stenosis is one of the major causes of hypertension and/or renal insufficiency. Without proper treatment, the condition often worsens progressively. Some renal arteries may narrow further until they become completely blocked, gradually deteriorating kidney function. In some patients, this can progress to end-stage renal disease.

Is renal artery stenosis common?

It is estimated that renal artery stenosis affects about 1%–3% of the hypertensive population and up to 20% of those with secondary hypertension. The condition is relatively common among the elderly. A foreign study showed that 6.8% of hypertensive patients over 65 years old also had renal artery stenosis. Based on China's "12th Five-Year Plan" national hypertension prevalence survey, about 26.6% of adults aged 18 and above have hypertension, suggesting a large total number of renal artery stenosis cases in China. However, the overall incidence of the disease is not high, accounting for 1%–5% of moderate to severe hypertension cases.

SYMPTOMS

What are the main manifestations of renal artery stenosis?

• Renovascular hypertension: A type of secondary hypertension characterized by onset typically under age 35 or over 55, with a higher prevalence in younger individuals. Key features include sudden onset or rapid worsening of hypertension in previously normotensive individuals, or abrupt exacerbation in those with preexisting hypertension. It responds well to RAAS inhibitors (e.g., captopril, valsartan) but poorly to other antihypertensive drugs.

• Ischemic nephropathy: Urine formation depends on glomerular filtration and tubular reabsorption. Renal tubules are highly sensitive to ischemia, leading to impaired concentrating ability (manifested as nocturia with low urine specific gravity and osmolality—increased urine volume but reduced concentration). Subsequently, glomerular filtration rate (GFR) declines, impairing toxin excretion (e.g., elevated serum creatinine due to reduced filtration).

• Since renal artery stenosis is primarily caused by atherosclerosis, it often coexists with cardiovascular or cerebrovascular atherosclerotic diseases, such as stroke or coronary artery disease.

CAUSES

What causes renal artery stenosis?

The etiology of this disease is complex and is generally divided into two categories: atherosclerotic and non-atherosclerotic.

• Atherosclerosis: Accounts for about 70% or more, commonly occurring in middle-aged and elderly individuals. These patients often exhibit manifestations of atherosclerosis in other systemic arteries, while isolated renal artery atherosclerosis is rare.

• Non-atherosclerotic: Causes of non-atherosclerotic renal artery stenosis include: Takayasu arteritis, fibromuscular dysplasia (FMD), thrombosis, embolism, aortic dissection involvement, trauma, congenital renal artery abnormalities, polyarteritis nodosa, Behçet's disease, post-radiation scarring, compression by surrounding tumors or bands, etc. Takayasu arteritis and FMD are the most common.

How does renal artery stenosis cause hypertension?

First, hypertension is a systemic disease, though it is often monitored via the brachial artery. Second, renal artery stenosis can lead to renal ischemia, stimulating the secretion of renin (a substance measurable in the blood), thereby activating the renin-angiotensin-aldosterone system (RAAS). This causes vasoconstriction and impaired sodium-water excretion, resulting in hypertension. Many antihypertensive drugs, such as captopril and valsartan, work by blocking this system to lower blood pressure.

Does renal artery stenosis always cause hypertension?

Not necessarily. Only when renal artery stenosis activates the renin-angiotensin-aldosterone system (RAAS) does it lead to hypertension.

DIAGNOSIS

What tests should be done for the diagnosis of renal artery stenosis?

Plasma renin activity, Doppler ultrasound, magnetic resonance angiography (MRA), CT angiography (CTA), arterial angiography, digital subtraction angiography, etc.

Why are these tests performed for the diagnosis of renal artery stenosis?

• Plasma renin activity: Used to assess RAAS activity, primarily for screening renal vascular hypertension. However, it does not identify the location of stenosis or aid in diagnosing renal ischemia.
• Doppler ultrasound: A non-invasive test that can detect the location and severity of renal artery stenosis.
• Magnetic resonance angiography (MRA): A non-invasive, radiation-free method that does not require iodinated contrast (suitable for patients with renal insufficiency). It can visualize proximal renal artery stenosis but not distal segments. Not suitable for individuals with magnetic implants or claustrophobia.
• CT angiography (CTA): Compared to MRA, CTA is cheaper, more convenient, and faster. However, it requires a large amount of contrast agent and is unsuitable for those with contrast allergies or renal insufficiency.
• Arterial angiography: The gold standard for diagnosing renal artery stenosis, but it is invasive, involves radiation, is expensive, and carries more complications.

If one test is the most definitive for diagnosing renal artery stenosis, why not skip other tests and proceed directly with it?

Renal artery stenosis is a rare condition, and clinical suspicion varies from low to moderate to high. Each test has its advantages and disadvantages. Arterial angiography is performed only when suspicion is high. For low or moderate suspicion, non-invasive tests like ultrasound or MRA are preferred to save costs and reduce risks. Confirmatory tests are conducted only if preliminary results are positive.

Are there specific diagnostic criteria for renal artery stenosis?

Based on the etiology of renal artery stenosis, the diagnostic criteria for the following three causes are detailed: atherosclerotic, Takayasu arteritis, and fibromuscular dysplasia (FMD).
Diagnostic criteria for atherosclerotic renal artery stenosis:

• At least one risk factor for atherosclerosis (obesity, diabetes, hyperlipidemia, age >40 years, long-term smoking).
• At least two imaging findings of atherosclerosis (tapered stenosis or occlusion of the renal artery, eccentric stenosis, irregular plaques, calcification, predominantly involving the proximal segment and ostium of the renal artery; evidence of atherosclerosis in other abdominal vessels).

Diagnostic criteria for Takayasu arteritis-related renal artery stenosis:

• Onset age <40 years, more common in women.
• Symptoms and/or signs of vascular involvement (ischemia in affected organs, signs related to vascular stenosis, pain in affected vessels during acute phases, and elevated inflammatory markers).
• Characteristic imaging findings on duplex ultrasonography (DUS), CTA, MRA, or renal angiography, excluding atherosclerosis, FMD, congenital vascular malformations, connective tissue diseases, or other vasculitis. This standard requires meeting all three criteria, with at least one item from each.

Diagnostic criteria for FMD-related renal artery stenosis:

• Imaging findings: Classified as multifocal (beaded appearance), unifocal (length <1 cm), or tubular (length >1 cm). Lesions are mostly located in the mid-to-distal segment of the main renal artery and may involve primary branches. Severe stenosis often shows collateral vessels from the proximal renal artery or adjacent lumbar arteries. Unifocal lesions may exhibit distal aneurysmal dilation.
• Diagnosis is confirmed in young patients (mostly <40 years) with the above imaging findings, excluding atherosclerosis, renal artery spasm, Takayasu arteritis, or other vasculitis.

TREATMENT

Which department should I visit for renal artery stenosis?

Vascular surgery or nephrology.

How should renal artery stenosis be treated?

Treatment for renal artery stenosis includes multiple aspects:

• Treatment based on different causes:
  • For atherosclerosis, treatment mainly targets risk factors such as smoking cessation, lipid-lowering, blood pressure control, antiplatelet therapy, and glucose management, with a focus on lipid-lowering.
  • For Takayasu arteritis, the exact cause remains unclear, and treatment primarily targets nonspecific inflammation of the vascular wall. If clinically active, especially in the acute phase, aggressive anti-inflammatory therapy is generally recommended. Most guidelines suggest glucocorticoids as initial treatment, with immunosuppressants added if necessary.
• Treatment for renal hypertension: Medication is the foundation, including ACEIs/ARBs, calcium channel blockers, and beta-blockers. ACEIs/ARBs are the most targeted antihypertensive drugs and are recommended for most patients, but caution is needed for those with a single functional kidney or bilateral RAS.
• Revascularization therapy: Currently, percutaneous intervention is the preferred method, including balloon angioplasty and stent placement.

Under what circumstances should interventional therapy be considered for renal artery stenosis?

Angiography can identify the type and progression of lesions and guide treatment selection.

• Mild stenosis (<50%) does not require intervention.
• Moderate stenosis (50%-70%) with well-controlled blood pressure and stable renal function also does not warrant intervention.
• Stenosis >70% with any of the following is ideal for intervention:
• Requiring ≥3 antihypertensive drugs for blood pressure control.
• Progressive renal function deterioration (even unilateral).
• Unexplained heart failure or pulmonary edema.

Will blood pressure return to normal after surgery for renal artery stenosis-induced hypertension?

For fibromuscular dysplasia, 50%-60% of patients achieve cure, and 30%-40% show improvement. For atherosclerotic renal vascular hypertension, cure rates are lower, but more patients experience improvement.

Are other tests needed before renal artery stenosis surgery?

Preoperative evaluation is crucial, including ECG, blood tests, coagulation tests, and biochemistry. Fibromuscular dysplasia often affects younger, healthier individuals, posing lower surgical risks. Atherosclerosis patients are typically older and require coronary artery disease screening, as it is the leading cause of postoperative mortality.

After revascularization for renal artery stenosis, what indicates successful treatment?

Criteria for revascularization success:

• Anatomical success: Post-PTA residual stenosis <50%, or post-stent residual stenosis <30%.
• Hemodynamic success: Translesional systolic pressure gradient <20 mmHg, mean gradient <10 mmHg.
• Clinical success (assessed after ≥6 months):
  • Blood pressure:
    • Cure: No medication, BP <140/90 mmHg.
    • Improvement: Reduced medication/dosage with BP drop >10%.
    • Failure: No change or insufficient improvement.
  • Renal function: Improved/stable GFR, slower decline, or improved serum creatinine, cystatin C, or 24h urine protein.
  • Cardiovascular outcomes: Reduced risk of cardiovascular events.

Is nephrectomy necessary for renal artery stenosis?

With advances in revascularization and antihypertensive drugs, nephrectomy is rare. It is only considered for severe renal atrophy, irreversible vascular damage, or renal infarction.

Is follow-up needed after revascularization for renal artery stenosis?

Regular follow-up is essential: monitor blood pressure and renal function every 1-2 months, and perform renal/arterial ultrasound every 6-12 months to assess kidney size and blood flow. Isotope scans may be needed to evaluate split renal function.

DIET & LIFESTYLE

What should patients with renal artery stenosis pay attention to in daily life?

• The common causes of renal artery stenosis include atherosclerosis, Takayasu arteritis, and fibromuscular dysplasia. Therefore, it is important to reduce fat intake, exercise regularly, and actively manage the underlying condition.
• Maintain a light diet with low protein intake. Foods rich in high-quality protein, such as milk, eggs, lean meat, fish, and soy products, can be consumed but in moderate amounts.
• During the progression of chronic renal failure, conditions like hyperkalemia, hyperphosphatemia, and hyperuricemia may occur. Dietary adjustments should be made accordingly. For high blood potassium levels, reduce the intake of potassium-rich vegetables and fruits.

PREVENTION

How to prevent renal artery stenosis?

The key to prevention lies in vigorously preventing and actively treating the underlying diseases that cause renovascular hypertension, such as Takayasu arteritis and atherosclerosis.