Renal Artery Stenosis – Symptoms, Diagnosis, and Treatment of Renal Artery Narrowing

The kidneys are paired abdominal organs—there is one on each side. Normally, each kidney is supplied with oxygen-rich blood by a renal artery, the arteria renalis. This artery branches off from the aorta on both sides at the level of the first or second lumbar vertebra.

The kidneys are essential for filtering the blood and regulating blood pressure. If blood pressure drops for any reason, the kidneys counteract this through various mechanisms to raise blood pressure again. Only when blood pressure is sufficiently high can the kidneys properly perform their filtering function (cleansing the blood).

A renal artery stenosis refers to the narrowing of the renal artery. As a result, less blood—and thus less oxygen—reaches the affected kidney. In addition, the pressure downstream of the narrowing is lower, which effectively tricks the kidney into thinking that blood pressure has dropped throughout the entire body. As a result, the kidney attempts to raise blood pressure, which restores normal pressure within the kidneys but leads to elevated blood pressure (“high blood pressure” or arterial hypertension) throughout the body.

Renal artery stenosis is widespread in industrialized countries. Nearly half of all people over the age of 75 are affected. According to estimates and studies, up to five percent of all cases of high blood pressure are caused by renal artery stenosis.

If the stenosis develops after the age of 50, it is usually caused by atherosclerosis. This refers to the buildup of connective tissue, calcium, fat, and blood clots in the arterial blood vessels; it is also known as vascular calcification. These plaques cause the vessel wall to become stiffer and the vessel diameter to narrow, preventing blood from flowing properly.

There are various risk factors that can contribute to the development of atherosclerosis. These include:

• age
• being male
• a family history of the condition
• lack of physical activity
• Smoking and alcohol consumption
• Diabetes mellitus (diabetes)
• Elevated blood cholesterol levels
• High blood pressure
• Gout
• Overweight

In younger patients, renal artery stenosis develops primarily as a result of fibromuscular dysplasia (FMD). In this condition, the arterial wall thickens for reasons that are not yet fully understood. Renal artery stenosis can also result from vascular inflammations such as panarteritis nodosa or Takayasu’s arteritis.

The main symptom of renal artery stenosis is high blood pressure. Since this is caused by kidney disease, it is also referred to in medicine as renal hypertension. However, the kidney’s filtering function is also impaired by an upstream renal artery stenosis, which manifests in symptoms such as

• fatigue,
• exhaustion,
• decreased urine output, and
• fluid retention in the tissues (edema)

.

Why exactly does renal artery stenosis lead to high blood pressure?

Arterial hypertension resulting from renal artery stenosis is primarily mediated by the Goldblatt mechanism. Due to the stenosis, less blood reaches the kidney, resulting in lower blood pressure in the organ’s blood vessels. Special receptors in the kidney constantly measure the pressure in the renal arteries. If this pressure is too low, the kidney releases the hormone renin.

This activates the so-called renin-angiotensin-aldosterone system. This results in a gradual increase in arterial blood pressure as

• the blood vessels in the body constrict and
• more water and sodium chloride are reabsorbed by the kidneys.

Blood pressure in the body then rises, causing more blood to flow into the kidneys. As a result, the pressure in the renal vessels rises to a near-normal level due to the stenosis. However, the rest of the body’s blood vessels remain in a state of arterial hypertension.

High blood pressure, however, only develops once the blood vessel is more than 75 percent obstructed.

What symptoms result from high blood pressure?

High blood pressure can manifest through various symptoms such as

• headaches,
• dizziness,
• vision problems,
• nervousness,
• ringing in the ears,
• Shortness of breath,
• nosebleeds, and
• sleep disturbances

. Often, high blood pressure goes unnoticed or is barely noticed, which is the most dangerous aspect of this condition. Untreated high blood pressure can lead to permanent damage to all tissues and organs, such as the eyes, blood vessels, or the brain.

What happens when the renal artery is completely blocked?

If a blood clot (thrombus) causes a complete blockage of the vessel, a renal infarction occurs.

Due to the lack of blood flow and the supply of nutrients and oxygen, parts of the kidney tissue are destroyed. A severe renal infarction manifests with symptoms such as

• severe abdominal or flank pain,
• tenderness of the abdominal wall,
• blood in the urine, and
• urinary retention.

If no other organic cause of high blood pressure is found, renal artery stenosis is suspected. Other indicators of renal artery stenosis include:

• High blood pressure in women under the age of 50
• sudden fluid accumulation in the lungs
• Kidney failure (renal insufficiency)

During the physical examination, the patient’s abdomen and back are auscultated with a stethoscope. In nearly half of all patients with renal artery stenosis, a flow murmur is detected.

To confirm the suspected diagnosis, imaging techniques such as

• duplex ultrasound,
• magnetic resonance imaging (MRI) of the blood vessels, or
• digital subtraction angiography (DSA)

are used.

The DSA procedure, in particular, allows for a precise assessment of the condition of the blood vessels. However, this procedure is more complex and is also comparatively invasive. Therefore, it is used only when magnetic resonance imaging or ultrasound do not provide a clear result.

If the renal artery stenosis is caused by atherosclerosis, patients should definitely avoid risk factors. These include, for example, smoking. A long-term shift toward a healthier lifestyle is necessary. In addition, antihypertensive medication is essential to lower elevated blood pressure to normal levels.

If blood pressure cannot be lowered despite medication, the option of widening the narrowed area using a balloon catheter should be discussed. This is called percutaneous transluminal angioplasty (PTA). 

A small metal mesh tube (stent), which remains permanently in the vessel, can keep the renal artery open. If the narrowed vessel is bypassed using a prosthesis, this is referred to as a vascular bypass. Unlike PTA, however, this procedure requires an incision in the abdominal wall.

Without treatment, the renal artery can become increasingly narrowed, and the stenosis can eventually lead to kidney failure.

If left untreated, high blood pressure often leads to cardiovascular disease and damage to all tissues. It must be treated with medication, and multiple medications are often necessary.

Fibromuscular renal artery stenosis in younger women typically resolves in over 70 percent of patients following treatment. The prognosis here is significantly more favorable than in patients with renal artery stenosis caused by vascular calcification (atherosclerosis).