Renal artery stenosis

　　The common causes of renal artery stenosis include atherosclerosis, fibromuscular dysplasia, and large artery vasculitis. Large artery vasculitis is a chronic nonspecific inflammation of the aorta and its main branches, involving the renal artery to cause stenosis and renal ischemia, most common in women under the age of 30. Fibromuscular dysplasia of the renal artery muscle fibers is more common in young and middle-aged women, and the lesions are mostly located in the distal 2/3 of the renal artery and its branches. It can be divided into subtypes such as intimal fibrosis, medial fibromuscular dysplasia, and perimembranous or perimembranous fibrosis. Intimal fibrosis often combines with aortic dissection and thrombosis, and the lesions in the middle layer often appear like a string of beads. Atherosclerosis of the renal artery is more common in men over the age of 40, and the lesions mostly occur at the orifice or near the proximal 1/3 of the main renal artery.

　　The following are common complications of renal artery stenosis:

　　1, difficult-to-control hypertension, often greater than 200/120mmHg, with a significant increase in diastolic pressure, a short history, rapid progression of the condition, and asymmetrical blood pressure in the limbs.

　　2, severe retinopathy;

　　3, cerebral thrombosis;

　　4, heart failure;

　　5, myocardial infarction;

　　6, complications such as renal failure.

　　Renal artery stenosis can cause persistent hypertension, and sometimes the pulse in the upper limbs may not be palpable, with significant differences in blood pressure between the upper and lower limbs. Physical examination often reveals a murmur in the renal artery area, and the determination of differential urine volume shows a significant reduction on the affected side. Summarized as follows:

　　Signs and symptoms:

　　1. Hypertension: blood pressure is often greater than 200/120 mmHg, with a significant increase in diastolic pressure.

　　2. Asymmetry of blood pressure in the limbs.

　　3. Abdominal vascular murmur.

　　The key to preventing renal artery stenosis is to actively prevent and treat the primary diseases that cause renal vascular hypertension, such as polyarteritis nodosa and atherosclerosis. Forming good living habits is an important measure for preventing this disease. Through reasonable diet, moderate exercise, smoking cessation, moderate alcohol consumption, regular lifestyle, maintaining a relaxed mood, and actively treating primary diseases, the chance of developing the disease can be reduced.

　　In recent years, people have explored the use of new non-invasive imaging techniques to examine renal vascular diseases. For renal artery stenosis, the following examination methods can be used:

　　1. Captopril-Renin Stimulation Test

　　Under normal circumstances, after taking the angiotensin-converting enzyme inhibitor captopril, the negative feedback action of angiotensin II can enhance the body's hyperreninemic response, which is particularly prominent in patients with renal artery stenosis. One hour after taking oral captopril, the increase in plasma renin is significantly greater than in primary hypertension. The sensitivity and specificity of this test can reach 93% to 100% and 80% to 95% respectively.

　　2. Captopril-Radioisotope Renal Scintigraphy

　　When renal artery stenosis occurs, it stimulates the activity of the renin-angiotensin system, and the contraction of the efferent arterioles by angiotensin II helps maintain glomerular pressure and glomerular filtration rate. The use of angiotensin-converting enzyme inhibitors (such as captopril) to inhibit the production of angiotensin II can reduce glomerular pressure and glomerular filtration rate. Before and after taking captopril, radioactive isotope technology can more ideally detect unilateral renal ischemia, with sensitivity and specificity above 90%.

　　3. Doppler Ultrasound Technology

　　The combination of abdominal ultrasound for direct examination of the renal artery and Doppler technology for measuring renal blood flow is currently the most commonly used screening method for diagnosing renal artery stenosis. Statistics show that the positive and negative predictive values of this technique for diagnosing renal artery stenosis are both above 90%. Of course, the operator's experience is crucial for accurate diagnosis. The imaging of the renal artery during the examination is often affected by gastrointestinal gases, obesity, recent surgical procedures, and other renal blood vessels nearby. Sometimes, abdominal ultrasound to understand whether the kidneys have atrophy or morphological changes can also be used as a screening examination.

　　4. Magnetic Resonance Imaging (MRI) and CT Scanning

　　In recent years, magnetic resonance imaging (MRI) and tomography have also been used for the diagnosis of renal artery stenosis. The specificity of MRI diagnosis can reach 92% to 97%, and recent reports show that CT scanning is the most sensitive imaging examination for diagnosing renal artery stenosis, with sensitivity and specificity reaching 98% and 94% respectively.

　　The diet for renal artery stenosis should be light and balanced, including high-fiber foods such as fruits and vegetables, and high-protein foods such as eggs and soybeans. Avoid smoking, drinking, spicy foods, and stimulants like coffee.

　　Renal artery angioplasty is the first-line method for treating renal artery stenosis, followed by drug therapy. The specifics are as follows:
　　I. Surgical Treatment
　　1. Renal Artery Angioplasty
　　(1) Indications: ① Hypertension, if the blood pressure of the upper limb cannot be measured, refer to the blood pressure level of the lower limb; ② Unilateral or bilateral renal artery trunk or its main branches, luminal stenosis greater than 50%, without obvious renal atrophy; ③ Renal artery stenosis with a systolic pressure difference greater than 30mmHg or an average pressure difference greater than 20mmHg at the proximal and distal ends; ④ Unilateral renal artery stenosis RVRP≥1.5 and healthy renal vein PRA/remote inferior vena cava PRA (2) Treatment: The purpose of treatment is to correct renal vascular hypertension and prevent renal failure. The efficacy of angioplasty is closely related to the cause, with renal artery fibromuscular dysplasia having the best efficacy, with 95.5% of cases cured or improved, followed by arteritis at 84%, and atherosclerosis at only 54.5%.
　　2. Vascular Reconstruction or Autologous Kidney Transplantation
　　If the affected kidney is significantly atrophic, the renal function is severely impaired or lost, or there are widespread lesions in the renal artery branches, nephrectomy can be considered. For patients with bilateral renal artery stenosis, a combined treatment method of surgery and renal artery angioplasty can be used to achieve better therapeutic effects.
　　II. Drug Therapy
　　For patients who are not suitable for the above interventional or surgical treatments, long-term antihypertensive drug therapy can be considered. This disease has an unsatisfactory response to general antihypertensive drugs, and β-receptor blockers and calcium channel blockers can be used. Angiotensin-converting enzyme inhibitors are absolute contraindications for bilateral renal artery stenosis or single-functioning kidney (natural or artificial transplant). For renin-dependent hypertension caused by unilateral renal artery stenosis, angiotensin-converting enzyme inhibitors can be considered. Unilateral renal artery stenotic hypertension using AECI can reduce the blood pressure on the stenotic side of the kidney, decrease GFR, but increase blood flow to the healthy kidney, and increase GFR. Due to the blockage of systemic AngⅡ and renal intrarenal AngⅡ, renal sodium excretion is significantly increased, the opposite kidney pressure-natriuresis effect is significantly restored, extracellular fluid and intravascular blood volume return to normal, blood pressure decreases, but attention should also be paid to changes in renal function during medication.