Biology and Subtypes: ARAS vs. FMD
At a Glance
Renovascular hypertension is high blood pressure caused by narrowed kidney arteries activating the RAAS hormone pathway. The two main types are ARAS, caused by plaque buildup in older adults, and FMD, a structural artery issue often affecting younger women.
To understand why your blood pressure is high, it helps to think of your kidney as a sophisticated sensor for the entire body. When the blood flow into the kidney is restricted, this sensor “misfires,” leading to a biological chain reaction called the Renin-Angiotensin-Aldosterone System (RAAS) [1].
The RAAS Pathway: A Faulty Sensor
Imagine your body is a house and your kidneys are the thermostat. If the pipe leading to the thermostat is restricted, the sensor thinks the whole house is “cold” (low on blood and dehydrated), even if the rest of the house is actually “boiling” (high blood pressure).
- Renin Release: The struggling kidney releases a hormone called renin [2].
- Angiotensin II: Renin triggers the production of Angiotensin II, a powerful chemical that causes your blood vessels to tighten and narrow throughout the body [1].
- Aldosterone: The system also releases aldosterone, which signals your body to hold onto salt and water, further increasing the volume of blood in your system [1][3].
The result is a persistent, systemic rise in blood pressure that won’t come down until the “sensor” issue is addressed.
Subtype 1: Atherosclerotic Renal Artery Stenosis (ARAS)
ARAS is the most common cause of renovascular hypertension and is driven by the same biological process that causes heart disease [4].
- Who it affects: Typically older adults (over age 50-60), especially those with a history of smoking, high cholesterol, or diabetes [5].
- What it is: A buildup of fatty plaque (atherosclerosis) right at the opening of the renal artery where it branches off the main aorta [4].
- Treatment approach: Doctors usually prioritize “Optimal Medical Therapy” first—using medications to block the RAAS pathway and managing lifestyle factors—rather than jumping to surgery or stenting [6].
Subtype 2: Fibromuscular Dysplasia (FMD)
FMD is not caused by plaque or lifestyle factors; it is a structural disease of the artery wall itself [7].
- Who it affects: Predominantly women, often between the ages of 20 and 60, who may have no traditional risk factors for heart disease [8].
- What it looks like: On imaging, FMD often has a distinctive “string of beads” appearance [9]. This is caused by alternating areas of narrowing and small widened spots in the middle or far end of the artery [10].
- Treatment approach: Because FMD is a structural issue in otherwise healthy people, it is often treated with balloon angioplasty (widening the artery with a balloon) [11]. This procedure is highly successful in FMD and can sometimes even “cure” the high blood pressure entirely [12].
| Feature | Atherosclerotic (ARAS) | Fibromuscular Dysplasia (FMD) |
|---|---|---|
| Primary Cause | Fatty plaque buildup [4] | Abnormal cell growth in artery wall [7] |
| Typical Patient | Older, history of smoking/cholesterol [5] | Younger to middle-aged women [8] |
| Imaging Sign | Narrowing at the artery’s start [4] | “String of beads” in the artery [9] |
| First-Line Care | Medication (RAAS blockers) [6] | Often balloon angioplasty [12] |
Common questions in this guide
What is the difference between ARAS and FMD?
How do kidney problems cause high blood pressure?
How is Fibromuscular Dysplasia (FMD) usually treated?
What does a string of beads mean on my kidney imaging?
Will I need surgery if I have ARAS?
Questions to Ask Your Doctor
Curated prompts to bring to your next appointment.
- 1.Do I have ARAS or FMD, and what does the shape of the narrowing on my imaging tell you about the cause?
- 2.If I have FMD, should we screen other arteries in my body, such as the ones in my neck or head?
- 3.Is my blood pressure high because of too much salt retention or because my blood vessels are too tight?
- 4.For my specific subtype, is balloon angioplasty or medical management the more appropriate first step?
- 5.How does my age and lifestyle history affect which treatment path you are recommending for me?
Questions For You
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References
References (12)
- 1
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Collecting duct-derived (pro)renin receptor contributes to 2-kidney, 1-clip-induced ischemic nephropathy and renovascular hypertension in mice.
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PMID: 30354824 - 7
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Fibromuscular dysplasia: Rare case of secondary hypertension in young male.
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PMID: 35860166 - 9
Carotid artery fibromuscular dysplasia: Ultrasound and CT imaging.
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European heart journal. Case reports 2022; (6(1)):ytab522 doi:10.1093/ehjcr/ytab522.
PMID: 35106441 - 11
Cutting Balloon Angioplasty (CBA) for the Treatment of Renal Artery Fibromuscular Dysplasia (FMD) in Six Patients: 5-Year Long-Term Results.
Cotroneo AR, Amoroso L, Giammarino A, et al.
Cardiovascular and interventional radiology 2017; (40(4)):546-552 doi:10.1007/s00270-016-1536-6.
PMID: 28035431 - 12
Renal Autotransplantation for Uncontrolled Hypertension in Nonatherosclerotic Renal Artery Stenosis-2 Case Reports and a Brief Review of the Literature.
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Hypertension (Dallas, Tex. : 1979) 2024; (81(4)):669-675 doi:10.1161/HYPERTENSIONAHA.123.19878.
PMID: 38507507
This page explains the biology and subtypes of renovascular hypertension for educational purposes. Always consult your vascular specialist or nephrologist to determine the exact cause and treatment plan for your high blood pressure.
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