What is Renal Artery Stenosis?
Renal artery stenosis (RAS) is a condition characterized by the narrowing of renal arteries which can restrict the flow of blood to the kidneys. This can lead to renovascular hypertension (high blood pressure) and impaired kidney functions or renal failure. If only the artery to either of the two kidneys is affected, it is then known as one-sided or unilateral RAS. On the other hand, if the arteries to both the kidneys are narrowed, a two-sided or bilateral RAS is said to have formed.
RAS is also referred by its various alternate names, such as:
- Renal artery obstruction
- Ischemic nephropathy
- Chronic renal insufficiency
- Atherosclerotic renovascular disease
Renal Artery Stenosis ICD-9 Code
The ICD-9 code for RAS is 440.1.
Renal Artery Stenosis Causes
RAS is primarily caused by atherosclerosis in the majority of patients who are aged above 50 years. This is a condition which causes narrowing and hardening of the blood vessel walls from the inside. A sticky, fat-like substance known as plaque is deposited along the inner linings of the arteries due to the presence of high cholesterol. On the other hand, fibromuscular dysplasia is responsible for causing this disorder mostly in women who are aged below 40 years. It is characterized by an anomalous growth of cells within the arterial walls that results in constricting these arteries.
Picture 1 – Renal Artery Stenosis
There are also a number of other factors that might lead to RAS. These include the following:
- Arteritis
- Embolism
- Fibrous bands
- Neurofibromatosis
- Renal artery aneurysm
- Extrinsic compression, such as in neoplasms
- Rupture or dissection of renal artery aneurysm
Renal Artery Stenosis Risk Factors
A number of factors increase the risk of RAS for an individual. These include:
- Old age
- Smoking
- Diabetes
- Substance abuse
- Insulin resistance
- Being overweight
- High blood pressure
- High cholesterol levels
- Heavy consumption of alcohol
- Lack of proper physical activities
- Improper diet that is high on cholesterol, fats, sugar and sodium
Renal Artery Stenosis Symptoms
The various signs and symptoms of RAS include:
- Edema
- Nausea
- Dry skin
- Vomiting
- Numbness
- Headaches
- Nosebleeds
- Darkened skin
- Loss of weight
- Muscle cramps
- Sleep problems
- Loss of appetite
- Changes in vision
- Pulmonary edema
- Generalized itching
- Tiredness or drowsiness
- Malignant hypertension
- Difficulty in concentrating
- Sudden onset of kidney problems
- A quantitative decrease or increase in urination
- High blood pressure that aggravates suddenly and is difficult to manage
- Narrowing of arteries in other parts of the body, such as in the brain, the legs or the eyes
If the normal blood supply to the kidneys is depleted or disturbed, the kidneys respond to it by initiating a type of complex hormonal reaction known as renin-angiotensin-aldosterone system. This response is activated as a form of defense mechanism against lowered blood pressure and lowered volume of circulating blood. When there is a reduction in circulating blood, the blood levels of angiotensin 2 hormone increases. This hormone causes narrowing of the blood vessels within the kidneys. It works together with aldosterone to promote salt retention by the two kidneys as well as to maintain the blood pressure and blood volume. Although this is a normal hormonal response of the body, it can become abnormal or pathologic when there is narrowing of the renal arteries. In such cases, the kidneys receive less blood even if blood volume is normal. This can stimulate the production of aldosterone and angiotensin 2, which can result in an abnormal increase of the blood pressure, i.e. Renovascular hypertension.
Renal Artery Stenosis Diagnosis
Digital subtraction angiography is the gold standard for investigating whether a person is having RAS. The other diagnostic tests carried out to evaluate this condition include:
- Cholesterol levels
- Plasma renin activity
- Captopril challenge test
- Renal artery arteriogram
- Blood aldosterone levels
- Creatinine clearance test
- Auscultation with stethoscope
- Blood Urea Nitrogen (BUN) Test
- Doppler ultrasound of renal arteries
- Evaluation of refractory hypertension
- Blood test to evaluate creatinine levels
- Blood test to evaluate potassium levels
- Magnetic resonance angiography or MRA
- Computerized tomographic angiography scan
- ACE (angiotensin converting enzyme) inhibition renography
- Effects of captopril test dose on differential renal function evaluated by MAG3 scan
The diagnosis is guided by a standard clinical prediction rule.
Renal Artery Stenosis Differential Diagnosis
There are numerous health conditions which are closely associated with RAS due to similarities between them in their clinical appearance. While carrying out the diagnosis for RAS, a diagnostician should differentiate it from these conditions. The differential diagnoses for RAS include ensuring the absence of conditions like:
- Uremia
- Azotemia
- Hypertension
- Atherosclerosis
- Nephrosclerosis
- Acute Renal Failure
- Malignant Hypertension
- Renovascular Hypertension
- Chronic Glomerulonephritis
- Hypersensitivity Nephropathy
Renal Artery Stenosis Treatment
RAS can be treated with medications, surgery, diet, and lifestyle changes. The main goals of treatment are:
- Preventing RAS from progressing further
- Managing the symptoms of renovascular hypertension
- Removing the blockage of renal arteries
RAS that has not led to RVH or resulted in significant artery blockage does not need treatment.
Lifestyle Changes
Firstly, a patient should make some lifestyle changes that will promote presence of health blood vessels and arteries throughout the body. The ideal ways to prevent plaque from constricting the arteries are by maintaining a proper body weight, regularly exercising and eating healthy foods. If one smokes, he or she should quit the habit in order to protect the body from problems related to arterial blockage.
Medications
People having renovascular hypertension needs to take medications prescribed by a medical expert that lowers the blood pressure as well as slows the progression of renal disease. Medications such as angiotensin receptor blockers or ARBs and angiotensin-converting enzyme or ACE inhibitors have shown effectiveness in slowing the progression of renal problems. Many patients might need two or more medicines to manage their blood pressure. A diuretic can help the kidneys to remove fluid from blood. The doctor may also prescribe calcium channel blockers, beta blockers, and other medications to ease the blood pressure. Some individuals having RAS cannot take ARBs or ACE inhibitors due to their effect on the kidneys. Hence, the physician needs to check the patient’s kidney functions before recommending these medications. A blood thinner like aspirin as well as cholesterol-lowering medications that prevent deposition of plaque may be prescribed as well.
Surgery
Although surgical procedures were used previously to treat RAS caused by atherosclerosis, recent investigations have shown usage of medications having a better outcome than surgeries. However, surgeries can still be recommended for people having RAS caused by fibromuscular dysplasia or RAS that doesn’t improve with medication. Surgical procedures to treat RAS include angioplasty/stenting and Endarterectomy or a bypass surgery.
Angioplasty and stenting
This is a procedure which involves putting a catheter into the renal artery of sufferers – generally through the groin, as in catheter angiogram. A tiny balloon placed at one end of that catheter is inflated to flatten out the deposited plaque against the wall of the artery. A stent, which is a small-sized mesh tube, can be placed inside the artery for keeping the plaque flattened and the artery opened.
Bypass surgery or endarterectomy
In the procedure of endarterectomy, the plaque deposits are cleaned out which leaves the inside lining all smooth and clear. A bypass is created by a synthetic tube or a vein which connects the kidney to aorta. This functions as an alternate path for the blood to flow to the kidney. However, these procedures are generally not performed due to the high propensity of complications associated with them.
Diet
One should limit their intake of cholesterol, fats, sugar and sodium in order to prevent atherosclerosis as this can result in RAS. RAS patients with decreased kidney functions should limit intake of cholesterol, protein, potassium and sodium in order to slow down the rate of kidney failure.
Renal Artery Stenosis Complications
The following complications might develop if the symptoms of RAS progress to an advanced stage:
- Strokes
- Heart attack
- Heart failure
- Kidney failure
- Fluid retention
- Vision problems
- Aortic aneurysm
- Chronic kidney disease
- Poor supply of blood to the legs, resulting in peripheral vascular disease
Renal Artery Stenosis Prevention
The following preventive measures can allow an individual to prevent the development of atherosclerosis which can eventually lead to RAS:
Picture 2 – Renal Artery Stenosis Image
- Quitting smoking
- Getting regular exercise
- Losing weight if one is overweight
- Eating a proper, heart-healthy diet
- Limiting the consumption of alcohol
- Monitoring the blood cholesterol levels
- Managing blood sugar levels if one has diabetes
Renal Artery Stenosis Prognosis
The prognosis of RAS may vary from one patient to another. If left untreated, the condition can progressively lead to malignant hypertension and chronic renal failure. Nearly 50% to 55% of patients having atherosclerotic RAS have developed progressive arterial obstruction within first two years of their radiographic follow-up. Complete renal artery occlusion have been seen in such cases for almost 9% to 16%.