I. Etiology of renal artery stenosis.
① Aortitis: the most common cause of renal artery stenosis in the country. The lesion involves the whole artery, with the middle membrane being the most severe; 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. Most of the cases are seen in young and middle-aged women, and nearly 90% of the cases are under 30 years old.
② Atherosclerosis: It is the most common cause abroad and occupies the second place in China. It is more common in elderly men, and stenosis is mostly located at the opening of the renal artery (within 2 cm) more often, mostly involving both sides.
Fibromuscular dysplasia: renal artery stenosis mainly occurs in the middle 1/3-distant 1/3 segment, often extending to branches. It is more frequent in young people and more frequent in women than men. It may mainly invade the inner, middle or outer membrane.
④ Postoperative stenosis: mainly seen after renal transplantation, mostly caused by rejection.
II. Clinical manifestations of renal artery infundibulum.
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 increase in long-term hypertension or sudden hypertension develops rapidly, showing symptoms of malignant hypertension.
③ Epigastric vascular murmur, systolic murmur with high tone and continuity can be heard in epigastric region, renal region or back in 2/3 cases.
(iii) Radiographic manifestations of the lower extremity of the renal artery.
① Renal artery stenosis or occlusion: stenosis due to aortitis and atherosclerosis is mostly located at the root of the renal artery, away from the opening of the renal artery and the proximal 1/3 segment, while stenosis due to fibromuscular hyperplasia is mostly located in the middle and distal segments and can involve branches.
(ii) Post-narrowing dilatation: It is commonly seen in severe limited stenosis, which is mostly shuttle-shaped.
(③) Aneurysm formation: it can be spindle-shaped or beaded, and beaded is a typical manifestation of poor myofibrillar 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, in which the renal artery often shows general atrophy and thinning of the renal arterial trunk in addition to the normal size of the renal arterial opening.
Fourth, the treatment of renal artery stenosis.
Renal artery stenosis caused by this disease is traditionally treated surgically, and the main treatment means are nephrectomy of the affected kidney, renal autograft and extracorporeal renal vascular microscopic repair. Interventional treatment using renal artery balloon catheter dilation and extracorporeal renal artery stent implantation has the advantages of small trauma, safety, simplicity and good results, and is the preferred method for the treatment of renal vascular hypertension.
V. Indications for interventional treatment of renal artery stenosis.
① Trans-femoral artery access is generally chosen, and most PTRA and renal artery stenting can be completed. When the renal artery travels significantly to the pedicle, single-hook catheter or Simons catheter insertion can be chosen. 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 access routes mentioned above, it is important to choose good equipment. Tapered-tip catheters, ultra-slip guidewires, ultra-hard and ultra-long exchange guidewires should be necessary, and for those with 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 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 dilatation with a larger balloon can be considered according to the change in arterial pressure difference after dilatation and the review of the angiography.
⑤ When delivering 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 segment of the guidewire 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 in the opening of the renal artery, it is appropriate for the stent to enter the abdominal aorta by no more than 2 mm.
(7) Positioning of the stent before release is 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 farther than the proximal 1/3 of the renal artery and 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. This method is more accurate than the previous one, and is particularly suitable for stenting of stenoses in the opening of the renal artery.