Causes of stenosis and indications for surgery
Renal artery stenosis triggers a cascade of ischemic events. Clinically, it manifests as secondary arterial hypertension, impaired renal function, and a poorly understood condition — flash pulmonary edema (flash pulmonary oedema).
The leading cause of narrowing is atherosclerosis. The plaque typically affects the ostium of the vessel itself (ostium). For a long time, stenting was considered the gold standard, but major trials (such as CORAL) showed no benefits of routine stenting over conservative therapy.
Today, stenting is justified only under strict indications:
- Refractory arterial hypertension;
- Rapidly declining renal function;
- Critical stenosis (>90%) in a solitary kidney;
- Recurrent flash pulmonary edema;
- Acute kidney injury with preserved kidney size (>8 cm).
Angioplasty and stenting technique
Access is achieved via the femoral artery (transfemoral) in 90% of cases. The procedure is performed under heparin and antispasmodic administration.
- Low-profile systems (0.014–0.018 inches) are advanced into the artery through a guiding catheter (6–7F).
- Balloon angioplasty (PTA) is performed.
- For atheromatous lesions, a balloon-expandable stent (balloon-expandable) is deployed. This is necessary to prevent elastic recoil (elastic recoil) of the vessel.
Clinical nuance: the stent should protrude into the aortic lumen by 2–3 mm. Precise tuning of the C-arm tilt is critical to visualize the artery ostium without superimposing the aortic contour.
Specifics in fibromuscular dysplasia
In young individuals (especially females), a non-atherosclerotic etiology of stenosis should be suspected. The most common is fibromuscular dysplasia (accounting for about 10% of all stenoses).
Its classic morphological type is medial fibroplasia. On angiography, it presents with a “string of beads” (string of beads) appearance due to alternating areas of stenosis and microaneurysms. Unlike atherosclerosis, such lesions respond very well to isolated balloon angioplasty (without stent placement), often resulting in a complete cure from arterial hypertension.
Renal Denervation
Approximately up to 30% of patients with essential hypertension fail to reach target BP levels with medical therapy. Sympathetic hyperactivity is one of the causes.
Efferent and afferent sympathetic fibers run within the adventitial layer of the renal arteries. The essence of renal denervation (RDN) is introducing a specialized catheter-probe into the renal artery and ablating these nerves using energy impulses. The procedure is performed under local anesthesia as day-case surgery.
Briefly: answers to topical questions
What complications can occur during balloon angioplasty and stenting of the renal arteries?
During balloon angioplasty and stenting of the renal arteries, minor and major complications may occur. Their overall incidence ranges from 5% to 10%.
- Puncture site hematoma is a common minor complication, typically occurring in the groin.
- Renal artery injury is a rare major complication.
- Cholesterol embolization is a rare major complication.
- Loss of the kidney is a rare major complication.
What is the mechanism of flash pulmonary edema in renal artery stenosis?
Renal artery stenosis leads to a cascade of ischemic events in the kidney, fluid retention, secondary arterial hypertension, impaired renal function, and flash pulmonary edema (flash pulmonary oedema).
What medications are administered to the patient during an endovascular renal artery intervention?
Heparin and an antispasmodic drug are administered during endovascular renal artery intervention.
Class and exam questions
What is the best imaging modality when renal artery stenosis is suspected?
Contrast-enhanced magnetic resonance angiography (MRA) is the optimal method. However, gadolinium is contraindicated in patients with eGFR < 15 mL/min due to the risk of nephrogenic systemic fibrosis.
Why is a stent almost always placed in atherosclerosis rather than relying on balloon angioplasty alone?
Atherosclerotic ostial plaques are prone to elastic recoil (elastic recoil) after balloon inflation. The stent prevents this process.
In which layer of the artery do the target nerves for denervation run?
Sympathetic nerve fibers run in the adventitia (outer layer) of the renal artery.
What else to study on this topic
- Pathophysiology of flash pulmonary edema (flash pulmonary oedema)
- Embolization of complex bifurcation aneurysms using a "stent-in-stent" configuration
- Non-atheromatous arteritides: Takayasu arteritis, neurofibromatosis, Williams syndrome
- The issue of nephrogenic systemic fibrosis when using gadolinium
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