Renal artery stenosis
Renal artery stenosis is a narrowing of the artery that carries blood to the kidney. The decrease in blood flow that reaches the kidney conditions both the perfusion of blood from the organ and the influx of blood that reaches the kidney for purification. Renal artery stenosis is usually unilateral, although it can occur in both kidneys.
The main consequence of renal flow obstruction is the secondary arterial hypertension that occurs. The kidney, the organ that regulates blood pressure, receives less blood and produces hormones that increase blood pressure.
How is it produced?
The most frequent cause of this situation is the presence of atherosclerosis or atheromatosis in the wall of the artery, that is, the accumulation of cholesterol crystals and other substances inside the artery, which is known as atheroma plaque, which renal flow decreases.
The risk factors that lead to the appearance of an atheroma plaque are increased levels of cholesterol in the blood, diabetes mellitus, high blood pressure, smoking and sedentary lifestyle. A large number of patients suffering from renal artery stenosis due to an atheroma plaque present atheromatosis in other vascular territories, such as the coronary, carotid or cerebral arteries.
Another cause that can lead to renal artery stenosis is fibromuscular dysplasia. It is an alteration of the inner layer of the artery wall that causes the tissue that forms it to increase in size and, consequently, the caliber of the arteries is decreased. It usually affects mainly young women and despite showing a predominance of the renal artery, other vessels may be affected.
Less frequent causes of renal artery stenosis can be neurofibromatosis, scleroderma, or panarteritis nodosa, among others.
The mechanism by which renal artery stenosis leads to high blood pressure is as follows: the kidney produces a hormone called renin, which helps regulate blood pressure. The production of this hormone depends on the blood pressure levels of the body, so that the lower the blood pressure, the less blood flow. The kidney detects this decrease in flow and to ensure its blood supply and the body's blood pressure, it produces renin, which, released into the blood, activates two more hormones, angiotensin and aldosterone, which are responsible for contracting the vessels and retaining water and salts, mechanisms by which blood pressure is increased and therefore blood flow increases. Thus, due to the production of renin, angiotensin, and aldosterone, blood pressure, which was at the correct levels, appears abnormally high.
Symptoms
The main symptoms that renal artery stenosis produces is hypertension secondary to the mechanism discussed above. Hypertension can be asymptomatic, giving at most mild symptoms such as headache, fatigue or sometimes ringing in the ears, blurred vision or syncope.
In the long term, if blood pressure is not controlled, it can affect other organs, such as the heart, causing arrhythmia problems, hypertrophy of the muscular wall of the heart or angina pectoris. Sustained elevated tension can also affect the vessels of the retina. Likewise, arterial hypertension can cause neurological alterations, both by increasing the risk of cerebrovascular accidents, as well as by being able to produce hypertensive encephalopathy, an affectation of the brain due to increased blood pressure, with seizures, deterioration of the level of consciousness, edema of retinal papilla and increased pressure within the skull.
If the stenosis of the renal artery progresses, blood flow to the kidney is compromised, which can lead to renal failure, with symptoms of edema, proteinuria and a decrease in the ability to purify the plasma that passes through the kidney.
Diagnosis
Renal artery stenosis should be suspected in a patient under 30 years of age with high blood pressure, in patients with well-controlled high blood pressure that suddenly decompensates, and in patients with high blood pressure treated with various drugs and that does not respond to treatment.
The blood test will allow evaluating the preservation of kidney function, as well as the levels of risk factors for atheromatosis, such as glucose or cholesterol.
Initially, a Doppler ultrasound will be performed to noninvasively assess the renal arteries. The ultrasound will allow us to see a reduced kidney in size, the kidney that suffers from the stenosis of the renal artery, while the opposite kidney will suffer an increase in size, a consequence of compensatory hypertrophy to replace the function of the affected kidney. The Doppler will allow to appreciate defects in the blood flow of the renal artery affected by the stenosis.
Other non-invasive tests that allow assessment of renal artery stenosis are the measurement of plasma renin activity and the renogram. In the first test, plasma renin is measured at baseline and after administering an arterial hypotensive, captopril. Given the drop in blood pressure, the kidney should produce more renin, so that if the levels after the administration of captopril are extremely high, it will imply that there is an alteration in the secretion of renin by the kidney. The renogram allows us to evaluate kidney function using a substance labeled with a radioactive isotope and it will also be altered by renal stenosis and after the administration of captopril. These tests should not be performed if the stenosis is suspected is bilateral.
The test that will give the most precise and exact information is arteriography, which is based on the administration of an intravenous contrast and allows to see the state of the affected artery and the degree and level of the obstruction. A less invasive test is magnetic resonance angiography, which allows by reconstruction of magnetic resonance images to assess the state of the renal artery.
Treatment
The essential treatment will be based on the pharmacological control of arterial hypertension, with hypotensive drugs such as ACE inhibitors and ARBs. Likewise, an attempt will be made to correct other risk factors such as excess cholesterol or diabetes, if they exist.
However, the definitive treatment is to solve the obstruction of the renal artery. A surgical bypass of the obstructed area can be performed, that is, with a graft to save the obstructed area so that the blood does not pass through that area and can reach the kidney in greater flow.
A less invasive approach to unblocking the stricture is percutaneous intraluminal angioplasty. It consists of introducing a guide through the skin to access the arterial system and reach the obstructed renal artery. The advancement of the guide is followed by radiological control. Once it reaches the stenosis area, a catheter is passed with a balloon at the tip, which swells and dilates the obstructed area. In the same act, a stent can be placed, a helical element that once placed expands and prevents the vessel from closing. Safer than surgery, with this technique better results are obtained in cases of fibromuscular dysplasia than in those of atheromatosis, since in 35% of cases, if risk factors are not subsequently controlled, atheroma plaque can breed.
Precautionary measures
They are based on regular blood pressure control and reducing cardiovascular risk factors, such as eliminating tobacco, a healthy and varied diet, low in fat and salt, and regular physical activity.
(Updated at Apr 13 / 2024)