1.What is renal artery stenosis and what is its cause?
Renal artery stenosis (RAS) refers to unilateral or bilateral narrowing of the main trunk or branches of the renal artery caused by various reasons, and it is one of the most common causes of secondary hypertension. The causes of renal artery stenosis are complex and can be congenital or caused by aortitis, atherosclerosis, or abnormal development of the arterial wall; before the 1990s, aortitis was the first cause of renal artery stenosis in China. In the last decade or so, atherosclerosis has replaced atherosclerosis as the primary cause of RAS at present. Renal artery stenosis can occur in the main trunk or branches of the renal artery. As a result of renal artery stenosis, there is a significant difference in blood pressure before and after the stenosis site, leading to renal ischemia, which stimulates increased renin secretion in the body and activates the renin-angiotensin-aldosterone system, which in turn causes hypertension.
Atherosclerosis – mostly occurs in elderly patients.
Fibromuscular dysplasia – common in young people and also in Western countries.
Aortitis – more common in young women.
Other rare causes include congenital renal artery dysplasia, renal aneurysm, renal artery embolism, renal arteriovenous fistula, trauma or surgically induced renal artery injury. Usually, children with the disease are mostly congenital anomalies, young adults are mostly renal arteritis or fibromuscular hyperplasia, and the elderly are mostly atherosclerotic renal arteries.
2.What are the consequences of untreated renal artery stenosis?
(1) Renal vascular hypertension Hypertension is the main clinical manifestation of renal artery stenosis, and renal vascular hypertension is the second leading cause of secondary hypertension. It is characterized by stubborn hypertension, which is difficult to control by ordinary antihypertensive drugs.
(2) Renal atrophy Renal atrophy is a direct consequence of renal artery stenosis. Patients who develop renal atrophy mostly present with progressive renal insufficiency.
(3) End-stage renal disease (ESRD) One study analyzed a total of 683 patients who ended up on dialysis for ESRD in the last 20 years, and 83 of them (12%) were diagnosed as being caused by RAS. However, the effect of RAS on ESRD cannot be fully defined based on current data.
(4) Patients with recurrent pulmonary edema may have sudden or “recurrent” pulmonary edema in renal artery stenosis. Patients with severe bilateral or unilateral RAS may present with volume overload. Patients with unilateral RAS may also develop pulmonary edema due to angiotensin-mediated vasoconstriction, which can cause an increase in left ventricular afterload.
(5) Cardiovascular events Patients with RAS have a higher risk of cardiovascular events, which may be due to more severe systemic atherosclerosis. Patients with severe RAS have higher levels of angiotensin II in the body, which leads to peripheral arterial vasoconstriction and can induce coronary ischemia.
(6) Asymptomatic renal artery stenosis Patients with renal artery stenosis may also present with no clinical symptoms, but rather the presence of a renal artery stenosis lesion is detected during the course of coronary angiography and peripheral angiography. Patients with asymptomatic renal artery stenosis have a poorer prognosis compared to those without renal artery stenosis, and their prognosis is related to the degree of stenosis. One study found that the 4-year survival rate for asymptomatic, severe RAS (≥75%) found incidentally during cardiac catheterization was 57% compared with 89% for patients with non-severe RAS.
3. Why does renal artery stenosis cause hypertension?
This system protects the kidneys. When the blood pressure drops, the blood flow to the kidneys decreases, and this system sends a signal to raise the blood pressure and maintain the blood flow to the kidneys. Angiotensin constricts micro-arteries throughout the body and increases the resistance of peripheral blood vessels, which raises blood pressure, while increased aldosterone leads to increased blood volume, which also raises blood pressure. And when renal artery stenosis occurs, blood flow to the kidney is reduced, and this regulatory system, also thought to be caused by a drop in blood pressure, is similarly activated to raise blood pressure, leading to hypertension in patients with renal artery stenosis. This hypertension is intractable and difficult to control with medication. This type of hypertension caused by renal ischemia due to renal artery stenosis is clinically known as renal vascular hypertension. And in the late stage of the disease plasma renin levels are reduced and the mechanism of hypertension is dominated by impaired glomerular filtration rate and water and sodium retention in both kidneys.
4. Why some patients with renal artery stenosis were not found to have significant hypertension before?
As we said before, some patients with renal artery stenosis may have no specific clinical manifestations, and some patients with renal artery stenosis due to renal artery atherosclerosis may not develop hypertension, but present ischemic kidney disease, which gradually leads to glomerulosclerosis, tubular atrophy and interstitial fibrosis. The clinical manifestations are progressive renal decompensation (early onset of tubular concentration impairment, high nocturia, decreased urine specific gravity and osmolality; later, impaired glomerular function, decreased endogenous creatinine clearance and increased serum creatinine), mild urinary abnormalities (mild proteinuria, small amount of red blood cells and tubular pattern) and progressive reduction in kidney size (the size of the two kidneys is often asymmetric).
5.How to diagnose renal artery stenosis early? What are the conditions that indicate the possibility of renal artery stenosis?
The onset of renal artery stenosis is usually insidious, and there is a tendency for it to get progressively worse, so once symptoms appear, the diagnosis must be made before irreversible renal impairment occurs. Since there is no difference in clinical symptoms between hypertension caused by renal artery stenosis and primary hypertension, the diagnosis relies on a high degree of vigilance. Therefore, the possibility of the presence of this disease should be promptly thought of when some clinical clues are found, and the presence of the following conditions may suggest the presence of RAS
(1) The following types of hypertensive manifestations.
(1) Hypertension before the age of 30 years or severe hypertension after the age of 55 years.
(ii) Acute hypertension (sudden and persistent deterioration of previously controllable hypertension).
(iii) Persistent hypertension (difficulty in achieving target blood pressure when a combination of three antihypertensive drugs, including diuretics, is applied in sufficient doses).
(iv) Malignant hypertension (hypertension combined with acute target organ damage, such as acute renal failure, acute heart failure or new onset of optic nerve or other cerebral neuropathy and III-IV retinopathy).
(2) When new-onset azotemia or worsening renal function (elevated blood creatinine greater than 50%) occurs with the application of angiotensin-converting enzyme inhibitors (ACEI) or angiotensin receptor antagonist class (ARB) drugs, or when there is unexplained renal hypofunction in the elderly.
(3) Presence of unexplained renal atrophy.
(4) Sudden onset of pulmonary edema.
(5) Vascular murmurs can be heard in the abdomen.
(6) Significant asymmetry in the size of both kidneys on ultrasound and other examinations.
(7) Concomitant other vascular diseases, such as coronary artery disease, carotid artery stenosis or lower limb artery stenosis, etc.
6.What are the clinical manifestations of renal artery stenosis?
(1) Renal vascular hypertension Most patients with renal artery stenosis do not have a family history of hypertension, and it is characterized by rapid progression of hypertension, and blood pressure is not easily controlled. Diastolic blood pressure increases significantly (often exceeding 110-120 mmHg) and may manifest as malignant hypertension (rapid rise in blood pressure, diastolic blood pressure persistently greater than 130 mmHg with headache, blurred vision, fundus bleeding, exudation and papilledema, even sudden blindness, grand mal seizures, persistent proteinuria, hematuria with tubuluria).
(2) Abdominal and lumbar murmurs can be heard in about 50% of patients at 2-7 cm above the umbilicus and 2.5 cm to the right and left.
(3) Primary manifestations caused by atherosclerosis or aortitis often have primary manifestations. The former occurs mostly in the elderly and may present with stroke, coronary artery disease, peripheral atherosclerosis and fundus changes; the latter is mostly in young women and may present with fever, arthralgia, pulselessness and other manifestations.
(4) Others: some patients have hyperaldosteronism (leading to hypokalemia), mild urinary abnormalities, and impaired renal function (ischemic kidney disease).
7.What tests are needed for patients with suspected renal artery stenosis?
(1) Routine tests include routine blood, urine, stool and blood biochemical tests. Anemia is often a sign of renal insufficiency, and the possibility of renal artery stenosis should be thought of. Blood creatinine and endogenous creatinine clearance are the most commonly used indicators to determine renal function. Hypokalemia is a manifestation of secondary aldosteronism.
(2) Imaging examinations.
(1) Ultrasound of both renal arteries: Ultrasound findings of a difference in the length diameter of the two kidneys greater than 1.5 cm can often indicate the possibility of renal artery stenosis on the side of the small kidney. Color Doppler ultrasound can observe the renal artery trunk and intrarenal blood flow changes. Compared with imaging, its sensitivity is 84% to 98% and specificity 92% to 99%. It can also be used to measure the renal artery resistance index, and an increase in the index indicates small renal artery sclerosis or glomerulosclerosis. It can also determine the effect of renal artery after recanalization.
(ii) Renal plasma renin-angiotensin system tests and renin stimulation tests: are not necessary for the diagnosis of renal artery stenosis, but some endocrine tests can sometimes be very useful in certain cases.
③Renal artery CT and/or MRI: CT and MRI examination of the renal artery can reveal the site and extent of stenosis.
④Renal arteriography: the most diagnostic value (golden indicator). It can clarify the lesion site, scope, severity, and formation of collateral circulation, and the treatment can be performed at the same time of imaging. Atherosclerotic lesions are mostly in the beginning of the renal artery and the abdominal aorta. Atherosclerotic lesions are more often found in the descending aorta and the proximal 1/3 of the renal artery. Fibromuscular dysplasia lesions are mostly in the distal 1/3 segment of the renal artery and its primary branches.
8.What does the treatment of renal artery stenosis include?
(1) Internal drug treatment: It cannot improve the ischemia of the affected kidney and can only help control hypertension. However, lowering the blood pressure can prevent complications caused by hypertension, such as cerebral hemorrhage, hypertensive encephalopathy, acute renal failure, and aortic coarctation. It is very important to lower the blood pressure quickly in such cases. The usual treatment of hypertension should not be neglected. ACEI drugs and calcium antagonists can effectively control hypertension in patients with RAS and delay the progression of renal disease. ACE inhibitors and ARB can effectively treat hypertension caused by unilateral RAS. beta blockers are effective drugs for the treatment of hypertension due to RAS. Diuretics can also lower blood pressure to target levels in RAS patients.
(2) Hemodynamic reconstruction therapy: Surgical treatments for renal artery stenosis can be divided into two main categories, namely, transabdominal renal artery reconstruction surgery and percutaneous transluminal renal arterioplasty. Regardless of the treatment, the goal is to make the narrowed renal artery smooth, so that the blood flow in the kidney can be restored to normal levels and the blood pressure regulating system in the kidney can no longer release the “signal” that raises blood pressure, thus lowering the patient’s blood pressure.
Percutaneous Transluminal Renal Arterioplasty. This is performed by puncturing the femoral artery at the root of the thigh, inserting a catheter with a balloon into the narrowed renal artery, and then inflating the balloon with contrast to dilate the narrowed renal artery from the inside out to a normal caliber, especially for patients with fibromuscular dysplasia. Since patients with atherosclerosis and aortitis are prone to restenosis and treatment failure after dilatation, these patients can be placed with a stent after dilatation to prevent postoperative stenosis. This procedure was invented by a Swedish physician in 1978 and has the advantages of minimal trauma, safety, and rapid postoperative recovery, and is now widely used worldwide as the preferred treatment for renal artery stenosis.
(3) Indications for endoluminal treatment Endoluminal treatment is indicated for.
(i) Patients with significant hemodynamic abnormalities and combined with the following conditions of RAS: acute progressive hypertension, intractable hypertension, malignant hypertension, hypertension combined with unexplained unilateral renal shrinkage, and hypertension intolerant to medication.
(ii) Patients with RAS with bilateral RAS or isolated kidney in combination with progressive chronic kidney disease.
(iii) Patients with RAS of significant hemodynamic significance and patients with unexplained, recurrent congestive heart failure or unexplained sudden pulmonary edema in combination with RAS.
(iv) Patients with hemodynamically significant RAS in combination with unstable angina.
There are some insurmountable disadvantages of percutaneous transluminal renal arterioplasty, such as low success rate, high recurrence rate of stenosis, etc. Some patients are unable to undergo the procedure due to contrast allergy, twisted iliac artery, etc., and then they have to resort to traditional transabdominal renal artery reconstruction procedures, including: abdominal aorta-renal artery bypass, renal artery endarterectomy, renal artery stenosis segment resection with end-to-end anastomosis If the above treatment is not possible, resection of the diseased kidney may be considered. Abdominal aorta-renal artery bypass surgery, also known as renal artery “bypass” surgery, is a surgical procedure in which a section of the saphenous vein is taken from the patient’s thigh, one end is anastomosed to the patient’s abdominal aorta, and the other end is anastomosed to the patient’s renal artery by bypassing the stenotic segment of the renal artery, so that the blood flow from the abdominal aorta is bypassed to the kidney to solve the patient’s renal ischemia. The disadvantage of this surgical approach is that it is more invasive, but the treatment results are very reliable and can also be used to treat patients who are not suitable for percutaneous transluminal renal arterioplasty.