Brief overview
- Course and prognosis: disease development sometimes over years; untreated high risk of late complications such as hypertension and renal failure; frequent relapses despite therapy
- Symptoms: Vascular stenosis itself is asymptomatic; usually accompanying symptoms due to high blood pressure such as dizziness, headache, nausea, visual disturbances, low exercise tolerance, possibly shortness of breath
- Causes and risk factors: Arteriosclerosis (hardening of the arteries), congenital defect in the structure of the vessel wall (fibromuscular); increased risk in obesity, metabolic diseases such as diabetes mellitus, smoking.
- Examinations and diagnosis: physical examination with listening to chest and abdomen, magnetic resonance imaging (MRI) and/or computed tomography (CT) including angiography, renal scintigraphy, digital subtraction angiography
What is renal artery stenosis?
The vascular bottleneck is either unilateral or bilateral. Since the kidneys play a major role in regulating blood pressure, in many cases the narrowed renal artery results in excessively high blood pressure (renovascular hypertension).
The Renin-Angiotensin-Aldosterone System (RAAS)
The specialized kidney cells of the juxtaglomerular apparatus first secrete the protein-cleaving enzyme renin. Renin now cleaves angiotensinogen – a protein produced by the liver – to angiotensin I. In the final step, another enzyme (angiotensin-converting enzymes) converts angiotensin I to angiotensin II. Angiotensin II finally causes the blood vessels to contract. This causes blood pressure to rise.
The activation of this reaction chain by renal artery stenosis is also referred to by physicians as the Goldblatt effect.
Is renal artery stenosis curable?
High blood pressure, which frequently occurs in this context, also usually results in further diseases, especially of the heart and circulation. Since arteriosclerosis in the respective renal artery is often only detected late and treatment is difficult at an already advanced stage, the prognosis here is also significantly less favorable. Hypertension often persists despite therapy and is not curable.
In principle, however, renal artery stenosis carries an increased risk of the blood vessel reoccluding itself after treatment.
The life expectancy of a renal artery stenosis ultimately depends on the extent of the vessel stenosis and on whether and how early it is treated.
What are the symptoms of renal artery stenosis?
In many cases, the symptoms of chronic, i.e. slowly developing renal artery stenosis are unspecific, because those affected do not notice the narrowed blood vessel itself. Although high blood pressure is a typical consequence of the vascular change, this in turn often causes hardly any symptoms at first. As the disease progresses, the following symptoms indicate that the blood pressure is too high:
- Dizziness
- Headache (especially in the morning)
- Nervousness
- Nausea
- Visual disturbances
If the vessel occlusion occurs acutely, i.e. suddenly, and both renal arteries may be affected, this is noticeable by a persistent and stabbing pain in the respective side of the body. Doctors refer to this as flank pain. In addition, there are signs such as abdominal pain, fever, nausea and vomiting.
How can renal artery stenosis be treated?
- The renal artery is at least 70 percent constricted.
- In the case of high blood pressure, which is difficult to control with medication.
- Pulmonary edema suddenly develops.
- When there is renal weakness (renal insufficiency).
- When there is fibromuscular renal artery stenosis (arterial narrowing caused by a thickened vessel wall)
Surgery for NAS
- Percutaneous transluminal renal angioplasty (PTRA): In this method, doctors insert a narrow, flexible tube (catheter) into the blood vessel in question. To remove the stenosis, they expand the section of the vessel with the help of a small balloon (balloon dilatation) or insert a small metal mesh tube (stent) that keeps the narrowed artery open.
Drug therapy for high blood pressure
If renal artery stenosis causes elevated blood pressure, affected individuals usually receive drug therapy. The aim is to lower blood pressure in order to prevent long-term damage and alleviate existing symptoms.
Other drugs of choice include angiotensin II receptor antagonists and renin inhibitors, which inhibit the renin-angiotensin-aldosterone system (RAAS).
In addition to drugs that delay blood clotting (anticoagulants), surgical treatment methods are usually the only options for treating acute renal artery stenosis.
What causes renal artery stenosis?
Doctors essentially distinguish between two forms of renal artery stenosis:
The most common cause of renal artery stenosis (NAS/NAST) is arteriosclerosis. Doctors therefore also speak of arteriosclerotic renal artery stenosis, or ANAST for short. It is the cause of vascular changes in 75 percent of cases and occurs more frequently in men than in women.
Fibromuscular renal artery stenosis:
About 25 percent of renal artery stenoses are due to this form. It usually affects younger women around the age of 30. In about 60 percent of those affected, the arteries of both kidneys are narrowed here. The cause of fibromuscular renal artery stenosis is a congenital defect in the structure of the vessel wall.
Risk factors and how to prevent
Smoking, obesity and diabetes mellitus are considered risk factors for vascular calcification. Although renal artery stenosis cannot be prevented in principle, it is possible to reduce the risk of vascular deposits:
- Do not smoke
- Maintain a healthy body weight or reduce weight if you are overweight
- Treat diabetes and have it controlled if you are diabetic
In most cases, excessively high blood pressure indicates possible renal artery stenosis. Often, the general practitioner notices by chance during a routine examination that the blood pressure is conspicuously elevated.
The following indications make the physician think of a renal artery stenosis:
- High blood pressure in young women around 30 years of age
- @ High blood pressure in men beyond the age of 50
- Hypertensive crises
- Sudden onset of pulmonary edema
- Evidence of renal impairment
If this suspicion is confirmed, the physician will arrange for further examinations. Renal artery stenosis can be detected with the help of the following imaging procedures:
Duplex sonography: This ultrasound procedure makes the blood flow within the blood vessel visible in color.
CT angiography (CTA): Computed tomography also produces slice images of the body, which, unlike MRI, are not produced by a magnetic field but with the help of X-rays. Similar to MRI angiography, a contrast agent makes the vessels visible, and the physician also assesses a three-dimensional image here.
