Renal Artery Stenosis Scan

Understanding Renal Artery Stenosis Scan

Renal artery stenosis (RAS) is narrowing of one or both renal arteries, most commonly caused by atherosclerosis or fibromuscular dysplasia. This narrowing reduces blood flow to the kidney, triggering the renin-angiotensin-aldosterone system and causing hypertension. When significant (＞70% diameter reduction), RAS can lead to resistant hypertension, progressive kidney dysfunction, and even kidney atrophy.

Renal scintigraphy with ACE inhibitor (captopril or enalaprilat) provides a functional assessment of renal artery stenosis. By comparing baseline and post-ACE inhibitor studies, the test determines whether a stenosis is hemodynamically significant and whether revascularization may improve blood pressure control or preserve renal function.

How Renal Artery Stenosis Scan Works

The scan evaluates renal perfusion and function before and after ACE inhibition:

Baseline study:

• Technetium-99m MAG3 or DTPA is injected intravenously
• Blood flow to each kidney is measured (1-2 minutes)
• Tracer uptake by renal parenchyma is assessed (2-5 minutes)
• Excretion into collecting system is evaluated (5-30 minutes)

ACE inhibitor challenge:

• Captopril (oral) or enalaprilat (IV) is administered
• The ACE inhibitor blocks efferent arteriole constriction
• In normal kidneys: Glomerular filtration is maintained
• In stenotic kidneys: Pressure drop reduces GFR, causing delayed excretion

Positive study criteria:

• Delayed peak uptake (＞5-6 minutes) in affected kidney
• Prolonged cortical retention (＞20-30 minutes)
• Decreased differential function (＞5-10% change)
• Asymmetrical renal size

Imaging Patterns

Atherosclerotic Renal Artery Stenosis

Atherosclerotic RAS typically shows:

• Older patients: Usually age ＞50 years
• Aorto-ostial location: Stenosis at renal artery origin
• Often bilateral: May affect both kidneys
• Associated vascular disease: CAD, PVD, carotid stenosis
• Gradual onset: Progressive hypertension

Scintigraphy findings:

• Small kidney on affected side (atrophy)
• Reduced differential function (＜40%)
• Delayed excretion after ACE inhibition
• Possible cortical retention

Fibromuscular Dysplasia

FMD shows a different pattern:

• Younger patients: Typically women age 20-50
• Distal renal artery: Mid to distal artery involvement
• "String of beads" appearance on angiography
• Often unilateral: Usually single kidney affected
• Normal kidney size: No atrophy typically

Scintigraphy findings:

• Normal kidney size on affected side
• Function may be preserved early in disease
• Marked delay after ACE inhibition
• Excellent response to angioplasty

Bilateral Renal Artery Stenosis

Bilateral disease presents challenges:

• Both kidneys show delayed excretion
• Global renal function may be reduced
• ACE inhibitor may cause significant GFR drop
• May be contraindicated if baseline GFR ＜30 mL/min

Clinical Applications

Evaluating Resistant Hypertension

When hypertension is difficult to control:

• Inadequate control despite 3+ medications
• Sudden onset or worsening of previously controlled hypertension
• Episodic flash pulmonary edema
• Young patient with severe hypertension

Scan helps determine:

• Whether RAS is contributing to hypertension
• Which kidney is affected (unilateral vs. bilateral)
• Whether revascularization may help

Assessing Revascularization Candidacy

Before angioplasty or stenting:

• Confirm stenosis is hemodynamically significant
• Assess viability of affected kidney
• Determine potential for BP improvement
• Predict renal functional recovery

Expected outcomes:

• Good response: 60-80% show improved BP control
• Better outcomes with unilateral disease
• FMD responds better than atherosclerosis

Post-Procedure Monitoring

After revascularization:

• Confirm improved perfusion and function
• Document successful intervention
• Monitor for restenosis
• Assess contralateral kidney

Evidence-Based Outcomes

Preparing for Your Scan

• Hydration: Drink plenty of water before the scan
• Medications: May need to hold ACE inhibitors or ARBs for 48 hours
• Blood pressure: Bring current medications list
• Diuretics: May need to hold if possible
• NPO: Usually no fasting required

Understanding Your Results

Frequently Asked Questions

What is the difference between atherosclerotic RAS and fibromuscular dysplasia?

Atherosclerotic RAS is caused by plaque buildup, typically in older patients with other vascular diseases. Fibromuscular dysplasia is caused by abnormal muscle cell growth in artery walls, typically in younger women. FMD responds excellently to angioplasty, while atherosclerotic RAS usually requires stenting.

Will angioplasty cure my high blood pressure?

Many patients (60-80%) experience improved blood pressure control after revascularization, and some can reduce or discontinue antihypertensive medications. However, complete cure is less common, especially in atherosclerotic RAS. Results are best with unilateral disease and FMD.

Is renal artery stenting a major procedure?

Renal artery stenting is a minimally invasive procedure performed through a small catheter inserted in the groin artery. Most patients go home the next day. The procedure takes 1-2 hours and has a low complication rate when performed by experienced operators.

What happens if I don't treat renal artery stenosis?

Untreated significant RAS can lead to worsening hypertension requiring more medications, progressive kidney dysfunction and atrophy, and increased risk of cardiovascular events. However, not all RAS requires treatment—incidental mild stenoses may be managed medically.

References

1. American College of Radiology. ACR Appropriateness Criteria: Renovascular Hypertension. 2024.
2. Society of Nuclear Medicine and Molecular Imaging. SNMMI Procedure Guidelines for Renal Scintigraphy. 2023.
3. Textor SC, et al. Renal Artery Stenosis: Evaluation and Management. Journal of the American Society of Nephrology. 2024.

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Medical Disclaimer: This information is educational only. Always discuss findings with your healthcare provider for personalized medical advice.