Aetiology

• Atherosclerosis (>85%).
  
• Fibromuscular dysplasia (10%).
  
• Intimal flap (e.g. dissection, iatrogenic trauma).
  
• Vasculitis.

Clinical Presentation

• Majority are asymptomatic (silent) discovered incidentally.
  
• Hypertension (most common symptom), often in younger patients.
  
• Acute (‘flash’) pulmonary oedema (due to severe hypertension).
  
• Renal dysfunction (due to malperfusion [controversial] or hypertension-related renal injury).

Pathophysiology

Hypoperfusion of the nephron stimulates sodium re-absorption in the proximal tubule with renin release from the juxta-glomerular apparatus (JGA). Circulating renin cleaves angiotensinogen to form angiotensin I (inactive), which in turn is converted to angiotensin II (AII) by ACE in the lung. AII acts on the AII receptor directly causing vasoconstriction (↑ BP) and stimulates aldosterone-release (adrenal cortex) which leads to Na⁺ and H₂O re-absorption in the distal tubule (↑ BP).

Ironically, the RAS-affected kidney may be protected from the hypertension by the stenosis, while the RAS-free contralateral kidney is exposed (leading to atrophy, scarring and eventually renal failure). The contribution of chronic post-RAS renal hypoperfusion towards ipsilateral renal insufficiency is unclear and controversial.

Complications of RAS