Renal artery stenosis is a renal vascular lesion in which the lumen of the renal artery is narrowed and renal blood flow is reduced due to various causes.
I. Etiology of renal artery stenosis.
1, aortitis: the most common cause of domestic renal artery stenosis. The lesion involves the whole artery layer, with the middle membrane being the heaviest; the renal artery lesion is mostly located at the opening of the renal artery or in the proximal segment, with a centripetal limited narrowing, or a bead-like narrowing and dilatation coexisting, with a more extensive collateral circulation. It is mostly seen in young and strong women, and nearly 90% of the cases are under 30 years old.
2, atherosclerosis: the most common cause abroad, in China occupies the second place. Older men are more common, and stenosis is mostly located at the opening of the renal artery (within 2 cm) more often, and mostly involves both sides.
3. Fibromuscular dysplasia: Renal artery stenosis mainly occurs in the middle 1/3 – distal 1/3 segment, often extending to branches. It is more frequent in young people, and more women than men. It may mainly invade the inner, middle or outer membrane.
4. Postoperative stenosis: mainly seen after renal transplantation, mostly due to rejection.
Other rare causes such as renal artery thromboembolism, arteriovenous fistula, and aneurysm can also lead to renal artery stenosis.
Second, the clinical manifestations of renal artery stenosis.
The clinical manifestations are mainly hypertension and renal insufficiency. Headache, dizziness, palpitations, nausea, blurred vision, etc. A few patients show aldosteronism, such as hypokalemia and hypertension.
Prolonged renal ischemia may lead to renal atrophy and renal insufficiency. On examination, a rough vascular murmur may be heard in the upper abdomen or renal area.
Features.
1, Age is usually less than 30 years old or more than 50 years old, and 78% of those under 30 years old.
2, Sudden exacerbation of long-term hypertension or sudden hypertension develops rapidly, showing symptoms of malignant hypertension.
3, epigastric vascular murmur, systolic murmur can be heard in the epigastrium, renal area or back in 2/3 cases, with a high tone and continuity.
III. Diagnostic points.
When renal artery stenosis is clinically suspected, intravenous pyelogram, radionuclide renal dynamic imaging, ultrasound, CT angiography, MRA and angiography can be performed. Ultrasound is convenient, non-invasive and economical. 2D ultrasound can show the size, shape and internal echo of the kidney, while color Doppler ultrasound can further show the lumen of the renal artery and measure blood flow velocity, resistance index and other indicators to diagnose stenosis and evaluate the degree of stenosis, which is the first choice for screening. CT angiography can clearly show the renal artery, especially in showing the collateral renal artery and vascular calcification, which has obvious advantages over ultrasound. CT can simultaneously scan other abdominal organs, such as the adrenal glands. if the renal arteries are normal but the adrenal glands are occupied, hypertension caused by adrenal pheochromocytoma should be suspected. MR and CT angiography can also obtain clear vascular images, and the former does not use iodine-containing contrast agents, reducing nephrotoxicity and making it more suitable for patients with renal insufficiency. Renal artery angiography has been considered the gold standard for the diagnosis of renal artery stenosis, which can clarify the presence or absence of renal artery stenosis, as well as the site, degree, extent and etiology of stenosis, and can be performed simultaneously with interventional treatment.
Renal artery stenosis angiographic manifestations.
1, renal artery stenosis or occlusion: stenosis due to aortitis and atherosclerosis is mostly located in the root of the renal artery, away from the opening of the renal artery and the near 1/3 segment, while stenosis due to fibromuscular hyperplasia is mostly located in the middle and distal segments and can involve branches.
2, post-narrowing dilatation: common in severe limited stenosis, mostly in the shape of shuttle dilatation.
3, aneurysm formation: it can be shuttle-shaped or bead-shaped, and bead-shaped is a typical manifestation of poor muscle fiber structure.
4.Lateral circulation formation: usually starts from renal pericyclic artery, lumbar artery, ureteral artery, etc.
5.On the basis of the above, there is delayed and shallow renal parenchymal visualization and renal atrophy. However, it should be distinguished from renal atrophy due to bilateral or unilateral chronic pyelonephritis, which often shows general atrophy and thinning of the renal artery trunk in addition to normal size of the renal artery opening.
Fourth, the treatment of renal artery stenosis.
1.Medical treatment is mainly antihypertensive treatment, and the effect of drug hypotension is not satisfactory in many patients.
2.Surgical treatment, the main treatment means for the affected nephrectomy, renal autotransplantation and extracorporeal renal vascular microscopic repair.
3.In recent years, percutaneous intracavitary angioplasty of the renal artery has become the first choice because of its small trauma, clear effect and mature technology, which is considered as an alternative therapy to surgical renal artery reconstruction. Long-term hypertension is prone to cardiac, cerebral and renal complications, and long-term renal ischemia can also lead to renal insufficiency and renal failure, so patients with recent renal decompensation and elevated blood creatinine should be treated more actively.
Interventional treatment using renal artery balloon catheter dilation and extracorporeal renal artery stenting has the advantages of being less invasive, safe and easy and effective, and is the preferred method for treating renal vascular hypertension. The method is to deliver a balloon catheter into the renal artery stenosis via femoral artery puncture and then dilate or place a stent to normalize the renal artery lumen and blood flow.
This treatment is effective in lowering blood pressure in most patients, and in some patients it also improves renal function. The technical success rate of renal artery balloon dilation with renal artery stenting is 90-100%. more than 70-80% of patients have varying degrees of postoperative blood pressure reduction. Studies reporting improvements in renal function vary widely, ranging from 30 to 70%. Stenting of the renal artery has been found to be more effective and durable than balloon dilation alone, but is more costly. Efficacy varies by etiology, with myofibrillar dysplasia being the most effective, atherosclerosis the second most effective, and aortitis the least effective.
Indications for interventional treatment of renal artery stenosis.
Renal artery balloon catheterization (PTRA) is preferred for renal artery stenosis with hypertension due to various causes, such as atherosclerosis, fibromuscular dysplasia, and polyarteritis major. Endovascular stenting is indicated for those with poor results or recurrence of conventional PTRA, those with stenosis at the opening of the renal artery, and those with intimal damage after PTRA of the renal artery. For renal artery stenosis after renal transplantation, PTRA is generally used (Figure 10-2-05), and endovascular stenting may be performed if necessary.
Technical points of renal artery balloon catheterization and stenting.
1. A transfemoral approach is generally used, and most PTRA and renal artery stenting can be accomplished. When the renal artery travels significantly to the pedicle, a single-hook catheter or Simons catheter insertion can be selected. When balloon catheter passage is difficult, a superior approach (axillary artery) can be used instead, which can lead to a much higher technical success rate.
2. Whether the catheter and guidewire, especially the balloon catheter and stent release system, can pass through the stenotic or occluded segment is the key to the success of the technique. In addition to the selection of the above access, it is important to choose good equipment. Tapered-tip catheters, ultra-slip guidewires, ultra-hard and ultra-long exchange guidewires should be necessary, and in cases of significant abdominal aortic tortuosity, ultra-long metal sheaths (40-50 cm, 8F) or 8F guiding catheters should be used. In the case of renal artery occlusion, a conformal contrast catheter should be inserted to its proximal end first, and then a super-slip guidewire should be rotated and advanced to “squeeze” through the occluded segment before following up with a tapered-tip catheter.
The size of the balloon can be selected according to the diameter of the proximal end of the stenotic segment of the renal artery as measured on the imaging film, and generally the diameter of the balloon should be equal to or slightly larger than 1 mm.
4. For stenosis at the beginning of the renal artery, since the lumen diameter cannot be measured correctly, a 6 mm balloon can be used for pre-dilatation, and whether to continue the dilatation with a larger balloon can be considered according to the change of the arterial pressure difference after the dilatation and the review of the angiography.
5.When sending the balloon catheter into the renal artery, the tip of the guidewire should be placed in the large branch of the renal artery and straightened so that the guidewire section in the stenosis has sufficient support.
When an internal stent is placed, a stent equal to or slightly larger than 1 mm in diameter of the corresponding renal artery should be selected, and its length should completely cover the stenotic segment and its two ends by 5 mm. For stenosis at the opening of the renal artery, it is appropriate for the stent to enter the abdominal aorta by no more than 2 mm.
7. The positioning of the stent before release is very important. The marking method can be used to determine the site of stenosis based on bony or artificial markings on the body surface, which is mainly used for stent placement in the proximal 1/3 of the renal artery and farther away, which is more convenient. The disadvantage of this method is that the superhard guidewire can cause changes in the straight course of the renal artery after delivery and can be misplaced if not done carefully. Another method of stent release and positioning is the contrast method, that is, when the stent is delivered to the predetermined position, the contrast is injected through a guide tube or a long sheath located at its opening or another pigtail catheter to visualize the abdominal aorta and the renal artery, and the proximal markings of the stent are observed to determine whether its position is correct. If necessary, adjustments are made and the stent is re-constructed for observation. The positioning accuracy of this method is higher than that of the previous one, and it is especially suitable for stent implantation in the stenosis of the opening of the renal artery.
V. Complications and management.
The incidence is about 1-5%. In addition to general angiographic complications such as bleeding or hematoma at the puncture site, there are complications due to balloon dilation or stent placement, such as local arterial entrapment; acute renal artery thrombosis; atherosclerotic plaque detachment leading to renal infarction; renal artery rupture and bleeding; stent displacement; restenosis, etc. Most of the complications are mild and can be cured by conservative treatment, such as thrombolysis by catheter in acute renal artery thrombosis; the use of distal umbrella of renal artery can prevent the occurrence of renal infarction; local entrapment can be solved by stent placement. Serious complications such as renal artery rupture are less common and require surgical treatment. Distant complications are mainly restenosis, of which myofibrillar dysplasia is the least common. The 5-year restenosis incidence of atherosclerosis is about 10-20%, and the restenosis incidence of aortitis is higher, up to 30-50% at 5 years. The restenosis can be solved by balloon dilation again for patients with restenosis.
Appendix: Renal artery stenosis refers to luminal narrowing of the renal artery ≥ 50%, expressed as a percentage of normal renal vessel diameter, i.e. renal artery stenosis (%) = 100 × (1 – stenotic lumen diameter / normal vessel diameter)
Indications for evaluation of renal artery stenosis by renal arteriography.
Clinical manifestations of renal vascular hypertension, ischemic nephropathy, or cardiac disorder syndrome with at least one of the following: (1) noninvasive angiography suggesting renal artery stenosis ≥ 50% (2) noninvasive angiography suggesting hemodynamically significant renal artery stenosis (3) noninvasive angiography is technically inadequate, diagnostic quality is questionable, or noninvasive angiography equipment is not available (4) age of onset of hypertension <30 years of age (5) proposed diagnosis of renal artery fibromuscular dysplasia as a cause of renal artery stenosis (6) recent hypertension in patients ≥60 years of age (7) reduction in renal volume or deterioration in renal function during pharmacological control of hypertension, especially in those on ACEI or ARB.