Renal artery stenosis

Question 1

What is renal artery stenosis?

Answer 1

Stenosis of the renal artery

Question 2

What is the aetiology of renal artery stenosis?

Answer 2

• Atherosclerosis
• Fibromuscular dysplasia: growth leading to stenosis, can be focal or multifocal; unknown aetiology but associated with collagen disorders, neurofibromatosis and Takayasu’s disease

Question 3

What is the pathophysiology of renal artery stenosis? (x4 points)

Answer 3

• Stenosis leads to reduced renal perfusion (ISCHAEMIC NEPHROPATHY) which activates RAAS leading to hypertension. When the stenosis leads to over 50% reduction in vessel diameter, this may cause uncontrollable hypertension
• Hypoperfusion also produces adaptive changes such as atrophy and fibrosis
• Ang-II also stimulates fibroblast activity. Fibrosis can lead to renal failure.
• There is also SNS activation leading to further hypertension

Question 4

How is renal artery stenosis categorised? (x3)

Answer 4

• Focal/multifocal
• Unilateral/bilateral
• Moderate (50%-70% stenosis), severe (>70% stenosis)

Question 5

What is the epidemiology of renal artery stenosis: How common is each aetiology? Age? Gender?

Answer 5

Atherosclerosis most common cause in elderly patients, and fibromuscular dysplasia in older. Fibromuscular dysplasia has onset typically before 30 years and more common in females.

Question 6

What are the signs and symptoms of renal artery stenosis? (x5)

Answer 6

• Hypertension (refractory to treatment) which may be accelerated
• Renal deterioration (on starting ACE inhibitor)
• Signs of renal failure in advanced bilateral disease (more common in atherosclerotic aetiology)
• Abdominal bruit may be heard over stenosed artery
• Sudden or recurrent oedema

Question 7

What are the investigations for renal artery stenosis? (x5)

Answer 7

• BLOOD: creatinine normal, hypokalaemia (from RAAS activation)
• URINALYSIS: normal in RAS, exclude other aetiologies
• DUPLEX USS: assess stenosis
• CT angiography/MRA: assess stenosis; caution over contrast use as many patients will have concurrent CKD
• RENAL SCINTIGRAPHY: radio-agent 99Tc-DTPA (excreted by glomerulus) or 99Tc-MAG3 (excreted by tubules) with addition of ACEi (captopril) causes delayed clearance by the affected kidney to work out (if the disease is unilateral) which kidney is affected (indicated by significant delay of peaked activity between kidneys)

Question 8

What might be seen in imaging in fibromuscular dysplasia?

Answer 8

String of beads – caused by multi-focal disease and areas of stenosis, each associated with microaneurysms.