Renal sympathetic denervation

Role of the renal sympathetic nervous system

The development and maintenance of elevated blood pressure is impossible without the direct involvement of the kidneys. The renal sympathetic nervous system (SNNS) operates in two main directions, forming a closed pathological loop.

Afferent innervation (from kidneys to central nervous system): The kidneys act as a powerful source of central sympathetic stimulation. This mechanism is actively engaged in arterial hypertension, heart failure, chronic kidney disease (CKD), and end-stage renal disease (ESRD).

Efferent activation (from central nervous system to target organs):

• Blood vessels: pronounced vasoconstriction occurs, leading to a global increase in vascular tone.
• Heart: heart rate (HR) and myocardial contractility increase.
• Kidneys: renal blood flow (RBF) and glomerular filtration rate (GFR) decrease. Simultaneously, renin secretion increases, sodium (Na+) is retained, and extracellular fluid volume increases.

Renal sympathetic denervation (RDN)

The technique was developed for patients with hard-to-control (resistant) arterial hypertension. The essence of the procedure consists in introducing a special catheter into the renal artery (e.g., the SPYRAL system with four electrodes) for radiofrequency action on nerve fibers.

Clinical history and evidence base:

1. Initially, the method showed high efficacy; however, the large SYMPLICITY HTN-3 trial (featuring a sham arm — a control group with a simulated procedure) revealed no advantage of denervation in lowering blood pressure compared to the placebo intervention. This led to a sharp decline in the use of the technology.
2. In 2016, the European consensus recommended not abandoning the method, but rather continuing in-depth research.
3. With the advent of new technologies (such as Spyral catheters), encouraging data emerged, which served as the launchpad for the global randomized clinical trial SPYRAL HTN in 2018.

Interventions for renal tumors

Today, endovascular interventions for Renal Tumours are almost entirely limited to life-saving hemorrhage control. The practice of preoperative embolization to facilitate surgical removal has become a thing of the past thanks to improvements in the surgical techniques themselves.

Benign tumors

They are relatively rare, yet require a clear management strategy:

• Oncocytomas: when small, they are extremely difficult to differentiate from malignant neoplasms due to similar morphology. They rarely bleed, so embolization is performed only in casuistic cases.
• Angiomyolipomas (AML): a more common pathology, often associated with tuberous sclerosis (multiple AMLs are a frequent cause of death in such patients). The main risk criterion is a size greater than 4 cm. At these dimensions, spontaneous hemorrhage occurs in 50–60% of cases, and one-third of patients are admitted to the hospital in a state of hemorrhagic shock.

Embolization technique: The method of choice is superselective embolization, which makes it possible to control bleeding in more than 90% of cases.

• Agents: microparticles, alcohol, and coils are used (often in combination).
• Target: action directly on the tumor's own vascular bed and occlusion of the feeding vessel.
• Result: thanks to superselectivity, the loss of healthy renal tissue function is minimal or absent.
• Complications: recurrent bleeding (rebleeding) requiring a repeat procedure is occasionally possible. Aneurysm rupture is extremely rare.

Management of malignant tumors

The absolute majority of malignant neoplasms are represented by renal cell carcinoma (RCC). In 85% of cases, these tumors are hypervascular (abundantly supplied with blood), which makes them an excellent target for embolization.

Spontaneous hemorrhage is a frequent occurrence in RCC and can be triggered even by a minor trauma in the history. It is often the hemorrhage that becomes the first clinical manifestation of cancer.

Features of embolization in RCC:

• If the second (contralateral) kidney functions normally, embolization of the entire affected kidney is considered the simplest and most reliable approach.
• Important technical nuance: placing occluding coils in the main proximal renal artery seems like a quick solution, but it is clinically recommended to perform distal embolization.
• Reason: malignant tumors often have parasitic blood supply from surrounding vessels (e.g., lumbar arteries). When only the main proximal trunk is closed, these collaterals continue to supply the tumor. Therefore, parasitic vessels must be carefully monitored and embolized if necessary.

Briefly: answers to topical questions

Class and exam questions

What else to study on this topic

• Pathogenesis of central sympathetic stimulation in chronic kidney disease and heart failure.
• Design of the SPYRAL catheter and physical principles of multi-electrode radiofrequency ablation.
• Association of angiomyolipomas (AML) with genetic mutations in tuberous sclerosis.
• Topographic anatomy of the lumbar arteries and the development of parasitic blood supply in renal tumors.

Other topics in the "Interventional radiology" section

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