Definition and Overview
Renal arteries are blood vessels that carry oxygenated blood to the kidneys. They enter the kidney through an opening called hilum and then branch off into smaller arteries that supply blood to the interior parts of the organ. The deoxygenated blood exits through the renal vein.
Stenosis is a medical term used to describe an abnormal narrowing of any passage of the body. Thus, renal artery stenosis means the narrowing of the kidney arteries. The condition prevents the kidney from getting enough supply of oxygen-rich blood. When the body senses that not enough blood is reaching the kidneys, it takes certain measures to address what it believes to be low blood pressure. This action can cause high blood pressure (systemic blood pressure) that can injure the kidney tissue. When left untreated, renal artery stenosis can lead to potentially life-threatening conditions including:
Heart failure, due to the hardening and narrowing of arteries that supply blood to the heart
Abnormal kidney function
Peripheral vascular disease, in which arteries that supply blood to other parts of the body, including the legs, are blocked
Causes of Condition
Renal artery stenosis can affect any person of any age, but it is most common in older people (>50 years old) who have hypertension, uncontrolled diabetes, abnormal cholesterol levels, and other vascular disease.
In the majority of cases, renal artery stenosis is caused by atherosclerosis in which plaque, which is made up of cholesterol, fat, calcium, and other substances found in the blood, build up inside any artery in the body. When little traces of these substances are left behind in the renal artery, they can accumulate and harden over time. This can cause the narrowing of the renal arteries as well as scarring of the kidney.
Rarely, the condition is caused by fibromuscular dysplasia, which causes abnormal growth within the wall of an artery. This results in narrow sections in the artery that makes it difficult for blood to flow through smoothly. The exact cause of fibromuscular dysplasia is unknown but it is believed to be congenital.
Other possible causes of renal artery stenosis are:
Compression of the kidney arteries due to abnormal growth or tumour on surrounding structures in the abdomen.
Vasculitis - An autoimmune disorder in which the blood vessels are attacked by the immune system, causing them to become inflamed.
Neurofibromatosis - A genetic neurological disorder that causes tumours to grow along nerves.
The renal arteries and their branches can also be blocked when a blood clot that has formed elsewhere in the body gets stuck in them or when they are damaged or injured during certain medical procedures. This is a more serious condition because it results in the total blockage of blood flow to the kidneys.
In general, the condition is not associated with any specific signs or symptoms. Thus, it is common for patients to not be aware of it or be diagnosed when the disease has already progressed. In some cases, patients who undergo routine tests or diagnostic procedures for unrelated medical problems, accidentally discover the condition. This is especially true for those who undergo imaging tests of the abdominal region as these create detailed pictures of the internal organs, including the kidneys.
When patients experience symptoms, they usually notice the following:
Acute high blood pressure that does not seem to respond to standard treatments
Signs of decreased kidney function, such as elevated protein levels in the urine
Accumulation of fluid in different parts of the body
Signs of heart failure
Who to See and Types of Treatments Available
Renal artery stenosis is diagnosed with a number of imaging and functional tests. These include blood and urine tests that measure the levels of hormones that regulate blood pressure and kidney function. Imaging tests, including a Doppler ultrasound, computed tomography (CT) scan, magnetic resonance imaging (MRI), and renal arteriography are also often performed to find the blockage and create detailed images of the renal arteries.
Treatment for renal artery stenosis depends on the degree of the narrowing. For mild cases, patients are often prescribed with medications and are advised to make lifestyle changes. These include maintaining a healthy weight, limiting salt intake, doing regular exercises, managing stress levels, and avoiding alcohol, illegal drugs, and smoking as much as possible.
High blood pressure is often successfully treated with medications. These include drugs that relax the blood vessel (angiotensin-converting enzyme or ACE inhibitors), remove excess sodium and water in the body (diuretics), and lower cholesterol levels.
If the condition is not responding well to home remedies and medications, minimally invasive surgical procedures are performed. These include angioplasty with stenting and artery bypass surgery. Both procedures aim to restore normal blood flow to the kidney, which results in immediate symptoms relief.
Angioplasty with stenting is a catheter-based procedure that does not require making a large incision in the abdomen to access the kidney arteries. It involves inserting a flexible hollow tube (catheter) into a small cut in the groin, which is then guided to the narrowed part of the artery with the help of an imaging technology. A guide wire is then inserted through the catheter and the balloon on its tip is used to widen the narrowed part of the artery. A fine mesh tube (stent) is usually used to keep the artery open and ensure normal blood flow. Renal artery bypass surgery, on the other hand, involves rerouting the blood flow using a substitute blood vessel. This provides a secondary route for the blood to reach the kidneys.
Renal artery stenosis. National Kidney and Urologic Diseases Information Clearinghouse. https://www.niddk.nih.gov/health-information/kidney-disease/renal-artery-stenosis.
Skorecki K, et al., eds. Renovascular hypertension and ischemic nephropathy. In: Brenner & Rector's The Kidney. 10th ed. Philadelphia, Pa.: Elsevier; 2016. http://www.clinicalkey.com.