Renal Vascular Disease

What is renal vascular disease?

The term “renal vascular disease” refers to several problems that can affect the blood vessels servicing the kidneys.  The word “renal” means that this condition relates to the kidneys, and “vascular” means that these problems have to do with vasculature, that is, the blood vessels that conduct oxygen-rich blood to the kidney away from the heart (arteries) as well as those that carry oxygen-poor blood from the kidney back to the heart (veins).  Each of a person’s two kidneys has an artery supplying it that branches off of the aorta and into smaller and smaller arteries before flowing through two sets of the tiniest blood vessels (capillaries) and converging back into veins.  Problems that prevent blood from flowing properly through the kidneys often cause high blood pressure that is unmanageable even when a patient is taking three blood pressure medications.  In fact, renal vascular disease is the most important cause of secondary hypertension (high blood pressure attributable to a known cause).

What are the types of renal vascular disease, and how are they different?

Renal vascular disease can refer to stenosis, thrombosis, atheroembolism, or aneurysm in an artery or vein supplying the kidneys. 

In patients with renal artery stenosis, an artery supplying one of the kidneys has become blocked and is limiting that kidney’s blood supply. 

Renal artery thrombosis and renal vein thrombosis occur when a blood clot forms in a renal artery or vein.  These blood clots can impede normal renal blood flow. 

In patients with atheroembolic renal disease, a large number of tiny crystals that have broken off of plaque that has formed due to atherosclerosis of another artery travel to the kidneys and lodge in the smallest arteries.  This process usually affects both kidneys simultaneously and equally.  These crystals prevent blood from reaching areas of the kidney and can cause kidney failure. 

When part of one of the renal arteries becomes more than 1.5 times its normal size because of local damage or weakness in the vessel, doctors call the problem a renal artery aneurysm.  Renal artery aneurysms are much less common than aneurysms in the thoracic and abdominal aorta.

What are the risk factors for renal vascular disease?

Most types of renal vascular disease are more common among older and female patients.  Other risk factors for renal vascular disease include smoking and conditions such as atherosclerosis, high blood pressure, high cholesterol, and diabetes.

What causes renal vascular disease?

Many different processes can cause the different types of renal vascular disease. 

Causes of renal artery stenosis
The arteries carrying blood to the kidneys can become narrowed due to atherosclerosis, fibromuscular dysplasia, or Takayasu’s arteritis.  Atherosclerosis is usually the cause of renal artery stenosis among the elderly.  It refers to the hardening of the arteries that occurs when a plaque made up of fatty deposits of cholesterol, cellular wastes, calcium, and other substances adheres to the inside lining of blood vessels. This build-up can reduce the size of the inside of the kidney arteries.  Fibromuscular dysplasia is a condition that most often affects young women and has no known cause, though a history of tobacco use and a positive family history for the disorder both increase a patient’s risk for developing the disease.  In patients with fibromuscular dysplasia, the muscle and fibrous tissues in some of their arteries become thick and hard, forming rings that reduce blood flow to the organs they supply.  Fibromuscular dysplasia can affect any organ in the body by reducing its blood supply; when the condition affects the renal arteries, it can cause renal artery narrowing (stenosis) as well as bulges called aneurysms between the thickened rings.  Occurring 4 to 9 times more often in women than men and particularly more prevalent among female Asians, Takayasu’s arteritis is a rare condition involving chronic inflammation of the larger arteries.  Though this condition usually affects the arteries of the arms and brain, it can affect the blood supply of any organ.  When affecting the kidney arteries, Takayasu’s arteritis can cause narrowing, a complete blockage, or bulges.

Causes of renal artery thrombosis and renal vein thrombosis
The renal blood vessels can become occluded if a blood clot develops because of trauma, infection, inflammatory disease, or renal artery aneurysm.  These clots can develop in both arteries and veins.  Pregnancy; vein compression due to an abnormally large, adjacent structure such as a tumor or renal artery aneurysm; nephrotic syndrome; steroid medications; and oral contraceptives can all cause clots to develop in the renal veins.  Nephrotic syndrome is a condition in which the parts of the kidneys that act as blood filters become damaged and allow too much protein to leak out of the blood and pass into urine. 

Causes of renal artery aneurysms
Bulges called aneurysms can occur in the arteries supplying the kidneys due to trauma, atherosclerosis, fibromuscular dysplasia, or congenital blood vessel weaknesses. 

Causes of atheroembolic renal disease
Severe atherosclerosis can cause atheroembolic renal disease without another aggravating condition, or some type of trauma can disturb moderate atherosclerosis to cause the disease. In this disease, tiny pieces of a plaque that has built up on the inner lining of a blood vessel break off and lodge in the small blood vessels in the kidneys causing them to become inflamed and preventing blood from reaching areas of the organs.  Cardiac catheterization and aortic surgery can cause atheroembolic renal disease because these procedures can aggravate the lining of an atherosclerotic aorta causing plaque crystals to break off into the bloodstream.

What are the symptoms, dangers, and complications of renal vascular disease?

The symptoms of renal vascular disease can be different for each of the different types of disease, but all of the types of renal vascular disease can cause kidney failure. 

Renal artery stenosis and renal artery thrombosis are important causes of high blood pressure because as they limit the amount of blood that can reach the kidneys, the kidneys respond by triggering the production and release of hormones that raise blood pressure in an effort to increase the amount of blood that can get to them.  Partially blocked renal arteries may cause no symptoms or a gradual onset of high blood pressure.  If an artery becomes severely blocked, symptoms can include fever; nausea; vomiting; urine discoloration; an excess of the waste product, urea, in the blood; and back pain.  If the blood supply to both of the kidneys becomes totally occluded, the kidneys completely shut down (acute kidney failure) and urine production ceases.  Sometimes, doctors will prescribe an angiotensin-converting enzyme (ACE) inhibitor or an angiotensin II blocker to a patient who they believe to have essential hypertension (high blood pressure with no identifiable cause).  Physicians commonly prescribe these medicines to fight high blood pressure, but if a patient’s blood pressure is gradually increasing due to progressive blockages in the renal arteries, the medicines may cause the patients kidneys to quickly fail.  This side-effect will reverse and the kidneys will start working again if the patient promptly stops using the medicine that is causing the problem (upon consulting his or her physician).

A chronic blockage in the renal veins usually does not cause symptoms, but if a vein is suddenly or severely occluded, symptoms such as severe pain between the ribs and the top of the hip, soreness in the area where the kidneys sit between the ribs and the backbone, and decreased kidney function may occur.

Atheroembolic kidney disease usually causes the kidneys to fail gradually, but when the condition has been caused by blood vessel trauma, it can rapidly affect the kidneys and cause their functioning to decline quickly.  Symptoms include decreased urine production as well as generalized symptoms such as fatigue, nausea, and appetite loss.  Atheroemboli can affect other areas of the body in addition to the kidneys.  The skin can become discolored or gangrenous and problems with circulation to a patient’s eyes can lead to blindness.  Small strokes can occur if atheroemboli reach blood vessels in the brain.

Renal artery aneurysms, like most aneurysms, usually cause no symptoms and are discovered during a diagnostic imaging test that was done to investigate a separate problem.  Hypertension (high blood pressure) is often present in patients with renal artery aneurysms and may or may not be associated with the aneurysm.  A dissecting aneurysm, which is an aneurysm that occurs when the innermost lining of an artery tears, may cause pain between the ribs and the top of the hip as well as blood in the urine. 

How do doctors diagnose renal vascular disease?

If a patient comes to his doctor with symptoms of a renal vascular disease, the doctor may want to use one or more of several available laboratory tests and imaging techniques to investigate the problem.  If the doctor suspects a blockage in the kidney blood vessels, he may want to see the results of laboratory tests such as a complete blood count, lactate dehydrogenase level, and urinalysis.  Lactate dehydrogenase levels are usually elevated when an organ has been damaged.  Physicians must use imaging techniques that show them a picture of what is happening in the kidneys in order to accurately confirm a diagnosis because the symptoms and blood tests are usually not sufficiently specific to rule out other possible causes.  Intravenous urography and radionuclide scanning can both show whether or not the blood flow to the kidneys is reduced.  Retrograde urography or an ultrasound of the kidney both can help a physician determine whether or not the cause of reduced blood flow to the kidneys is a renal vascular disease.  Angiography, also known as arteriography, is a more invasive, but also more definitive imaging technique that doctors may want to use to get x-ray images of the blood vessels around the kidney.  To obtain these images, a doctor must insert a small, flexible, hollow wire into an artery (usually the femoral artery in a patient’s leg), thread it to the kidney vessels, and inject a contrast dye that makes blood vessels show up on an x-ray.  Doctors usually only perform an angiography if they are considering a surgical intervention to fix whatever problem they believe to be present.  Spiral computed tomography (CT) is a technique that doctors can use as an alternative to angiography, because a spiral CT also gives an accurate picture of kidney veins. 

What are the treatment options for renal vascular disease?

If, during a diagnostic angiogram, a physician finds that a patient’s renal artery or one of its branches is reduced to at least 20% of its normal size, he or she may decide to perform an angioplasty.  Angioplasty is a minimally-invasive procedure in which a physician threads a catheter through a leg artery to an occluded blood vessel and inflates a balloon on the tip that expands to force the artery to become wider.  He or she may also place a stent at the same point in the artery in order to keep the vessel from collapsing.  If angioplasty and stent placement is insufficient to restore circulation to the restricted area, a patient may need to have an invasive, open surgery to remove a blockage or bypass the occluded point altogether.

Patients who have renal artery or vein thrombosis must often take anticoagulants (blood thinners) such as Coumadin or Warfarin in order to prevent further clotting and give the body a chance to dissolve the existing clot.  Thrombolytic medications actively dissolve clots and may be able to help a patient who has a severe blockage if he is able to restore blood flow to the restricted area within three hours of the initial clot.

Sometimes, doctors are unable to restore circulation and the kidneys shutdown.  When this happens and doctors cannot restore kidney function, it is called kidney failure.  If the underlying cause cannot be treated, the only treatment options for advanced kidney failure are dialysis or transplant.  Kidney failure occurs when the kidneys are no longer able to do their job, when they shut down and can no longer filter blood to remove wastes and monitor its volume and contents.  Dialysis is a treatment in which patients come to a treatment center several times a week to let a machine filter their blood.