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Renal Artery Stenosis

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Overview

Renal artery stenosis (RAS) describes the narrowing of the renal arteries and is most commonly due to atherosclerosis, followed by fibromuscular dysplasia (FMD). RAS generally presents with accelerated or difficult-to-control hypertension.

Pathogenesis of hypertension in RAS

Narrowing of the renal artery lumen can lead to decreased perfusion to the kidneys. This leads to the activation of the renin-angiotensin-aldosterone system (RAAS) which leads to the secretion of renin. Renin converts angiotensinogen to angiotensin I, which is then converted to angiotensin II by angiotensin-converting enzyme (ACE). Angiotensin II acts on the adrenal glands leading to aldosterone secretion, which leads to sodium and water retention and increased blood pressure.

Epidemiology

  • RAS due to atherosclerosis makes up 90% of cases
  • FMD makes up around 10% of cases
  • FMD is more common in women and typically occurs before 30 years of age

Presentation

Features and the patient’s history and background can point towards the underlying cause. Many patients may be asymptomatic and only have hypertension:

  • <30 years and hypertension – suggests FMD
  • >55 years and hypertension – suggests RAS due to atherosclerosis

Other features suggesting RAS include:

  • Severe, accelerating, and/or difficult-to-control hypertension
  • Biochemical and/or clinical evidence of renal dysfunction when starting ACE inhibitors or angiotensin II receptor blockers (ARBs) – they reduce renal perfusion even more
  • Sudden or unexplained recurrent acute heart failure in a hypertensive patient (‘flash’ pulmonary oedema)

Investigations

  • Urea and electrolytes (U&Es):
    • Urea and creatinine may be deranged
    • Potassium may be low or low-normal due to RAAS activation
  • Aldosterone:renin ratio:
  • CT angiography (CTA) and/or MR angiography (MRA):
    • First-line if FMD is suspected
    • MR angiography can be considered if CTA contraindicated
    • Angiography may show a ‘string-of-beads appearance’ in FMD

Management

Management involves optimising cardiovascular risks (e.g. smoking cessation, control of blood pressure, lipids and blood glucose etc.), avoiding ACE inhibitors or ARBs, and avoiding other nephrotoxic medications. Other management steps include:

  • Atherosclerotic RAS: angioplasty with stenting, particularly in flash pulmonary oedema. It may be considered in refractory or severe hypertension
  • FMD: percutaneous transluminal angioplasty with balloon dilatation with or without stenting

Complications

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