What is renovascular hypertension?

Renovascular Hypertension

Renovascular hypertension is the most common type of secondary hypertension, caused by reduced renal perfusion that activates the renin-angiotensin-aldosterone system, resulting in elevated blood pressure that can be corrected by treating the underlying renal artery stenosis. 1

Definition and Prevalence

• Renovascular hypertension accounts for 0.5-5% of all hypertension cases in the general population, but its prevalence increases to approximately 25% in elderly patients with end-stage renal disease 1
• It represents a form of secondary hypertension where the kidney "takes charge" of blood pressure regulation, elevating it to force blood through the blocked renal artery 2
• The defining criterion for true renovascular hypertension is a fall in blood pressure after intervention (angioplasty, stent placement, or surgery) 1

Etiology

• Renal artery stenosis (RAS) is the primary cause of renovascular hypertension, with two major pathologic entities:

  • Atherosclerotic disease (90% of cases) - typically affects the aorto-ostial segment and proximal 1 cm of the main renal artery 1
  • Fibromuscular dysplasia (10% of cases) - typically affects the middle and distal two-thirds of the renal artery and its branches, most commonly in young women 1

• Less common causes include:

  • Vasculitis
  • Embolic disease
  • Arterial dissection
  • Posttraumatic occlusion
  • Extrinsic compression of a renal artery or kidney
  • Renal artery aneurysms 1, 3

Pathophysiology

The mechanism of renovascular hypertension involves:

• Reduced renal perfusion triggers juxtaglomerular cells to release renin 4
• Renin catalyzes the conversion of angiotensinogen to angiotensin I 4
• Angiotensin-converting enzyme converts angiotensin I to angiotensin II 4
• Angiotensin II causes:
  • Peripheral arteriolar vasoconstriction
  • Increased renal tubular reabsorption of sodium and water
  • Stimulation of aldosterone release from the adrenal cortex
  • Increased sympathetic tone
  • Release of vasopressin 4
• These mechanisms collectively increase blood pressure through arteriolar constriction, enhanced cardiac output, and retention of sodium and water 4

Clinical Features Suggesting Renovascular Hypertension

• Abdominal bruit
• Malignant or accelerated hypertension
• Significant hypertension (diastolic pressure >110 mmHg) in a young adult (<35 years)
• New onset hypertension after age 50
• Sudden development or worsening of hypertension
• Refractory hypertension
• Deterioration of renal function in response to ACE inhibitors
• Generalized arteriosclerotic occlusive disease with hypertension 1

Diagnostic Approach

Imaging Studies for Suspected Renovascular Hypertension

For patients with normal renal function:

• Duplex Doppler ultrasound is the recommended first-line screening test (rating 9/9) 1
• MR angiography without and with IV contrast (rating 8/9) or CT angiography with IV contrast (rating 8/9) are also highly appropriate 1

For patients with decreased renal function (eGFR <30 mL/min/1.73 m²):

• Duplex Doppler ultrasound is the preferred screening test (rating 9/9) 1
• MR angiography without IV contrast is the second choice (rating 7/9) 1

Diagnostic Criteria

• Most investigators consider a 50-60% stenosis to be significant, although perfusion pressure in a large artery is generally not reduced until stenosis exceeds 70-75% 1
• Duplex Doppler ultrasound criteria:
  • Peak systolic velocity (PSV) in the main renal artery >200 cm/s (sensitivity 73-91%, specificity 75-96%)
  • Renal artery to aortic systolic ratio (RAR) >3.5 1

Treatment Options

• Medical therapy:

  • ACE inhibitors and angiotensin receptor blockers are effective but must be used with caution in bilateral renal artery stenosis or stenosis of a solitary kidney due to risk of acute renal failure 2, 5
  • Calcium channel blockers are also effective in patients with renal artery stenosis 5

• Revascularization (when medical therapy is ineffective or causes severe impairment of renal function):

  • Angioplasty with or without stenting
  • Surgical revascularization 2, 6

Important Considerations

• The goal of treatment is not only to control hypertension but also to preserve and restore renal function 6
• Bilateral renal artery disease presents a diagnostic challenge as it is difficult to quantify the effect on blood pressure of one side versus the other 1
• Fear of acute renal failure with ACE inhibitors or ARBs should not prevent their use in most patients, as this complication is rare (<5% of patients) and reversible with revascularization 2