Renal Artery Stenosis

Question 1

Define renal artery stenosis and the criteria that must be met

Answer 1

Narrowing of the renal artery lumen

It is considered angiographically significant if more than a 50% reduction in vessel diameter is present

Question 2

State and briefly explain the key risk factors for RAS

Answer 2

Dyslipidaemia- leads to atherosclerosis/cholesterol deposition in vessel walls → inflammation and progression of plaque

Smoking- favours endothelial inflammation and dysfunction. Associated with both atherosclerotic and fibromuscular dysplasia (FMD)

Diabetes- causes endothelial dysfunction; major cardiovascular risk factor.

Female sex- less strong. FMD more frequent than in males, atherosclerotic RAS more likely to progress

Question 3

State 2 key causes of RAS

Answer 3

Atherosclerosis 90% (older patients) -

• widespread aortic disease involving the renal artery ostia, often co-exists with CAD, IHD, stroke or PVD

Fibromuscular Dysplasia 10% (younger patients)

• Unknown aetiology- more common in females
• May be associated with collagen disorders, neurofibromatosis and Takayasu’s arteritis
• May be associated with micro-aneurysms in the mid and distal renal arteries (resembling a string of beads on angiography)

Question 4

Explain the pathogenesis of RAS

Answer 4

1. Renal hypoperfusion (due to the stenosis) stimulates RAAS
2. Increased angiotensin II + aldosterone→ increased systemic vascular resistance and sodium retention.
3. When the stenosis exceeds 50% reduction in vessel diameter, these regulatory mechanisms fail → worsening kidney function and difficult-to-control hypertension.
4. Hypoperfusion, hypertension and AGT2 cause fibrosis, glomerulosclerosis and renal failure

Question 5

Summarise the epidemiology of renal artery stenosis

Answer 5

• Prevalence unknown
• Accounts for 1-5% of all hypertension
• Fibromuscular dysplasia occurs mainly in women with hypertension < 45 yrs

Question 6

Recognise the presenting symptoms of renal artery stenosis

Answer 6

• presence of key risk factors- smoking, dyslipidaemia, and diabetes.
• onset of hypertension age >55 years- atherosclerotic RAS.
• history of accelerated, malignant, or resistant hypertension refractory to Tx
  
  • (which becomes worse on starting of ACE inhibitors)
• history of unexplained kidney dysfunction- due to progressive stenosis or hypertension-related end-organ damage
• History of multi-vessel CAD or PVD (suggests atherosclerotic RAS)
• History of flash pulmonary oedema

Question 7

Recognise the signs of renal artery stenosis on physical examination

Question 8

Identify appropriate primary investigations for renal artery stenosis

Answer 8

• serum creatinine + potassium
• urinalysis and sediment evaluation-
  
  • helpful in evaluating for glomerular source of kidney disease.
  • In the absence of co-existent diabetic nephropathy or hypertensive glomerulosclerosis, RAS is not associated with proteinuria or abnormalities in the urinary sediment
• aldosterone-to-renin ratio
  
  • ​<20 excludes primary aldosteronism as cause of hypertension and hypokalaemia or low-normal potassium

Question 9

Identify appropriate secondary investigations for renal artery stenosis

Answer 9

Non-Invasive

• Duplex ultrasound- shows the renal arteries and measures flow velocity as a means of assessing the severity of stenosis
• Ultrasound measurement of kidney size

Invasive

• Gadolinium-enhanced MR angiography (MRA): visualises the renal arteries and peri-renal aorta. Risk of contrast nephrotoxicity (contraindicated in stage 4/5 CKD)
• CT angiography- as for above
• Digital Subtraction renal Angiography = GOLD STANDARD (image) – but done after CT/MR as it is invasive
• Renal Scintigraphy
  
  • Uses radio-agent that is either excreted by glomerular filtration or by the tubules
  • Addition of an ACE inhibitor causes delayed clearance by the affected kidney (may not be useful in bilateral renal artery stenosis)