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MR angiography is probably the investigation of choice nowadays for suspected RAS. ACEI can cause worsening renal function and AKI in those with renal artery stenosis

About

• Potentially treatable cause of hypertension
• Suspect in older patients with atheroma
• Suspect in younger patients with hypertensions

Causes

• Fibromuscular dysplasia (20-40%): younger often female. Beaded appearance.
• Atherosclerosis: older patients. The lesion usually ostial within 1 cm of the proximal renal artery. Often have missing pulses, bruits and atheroma

Clues to diagnose RAS

Suspected renal artery stenosis if there is a greater than 25% reduction in eGFR within 3 months of starting (or increasing the dose of) a renin-angiotensin system antagonist, refractory hypertension, pulmonary oedema, and/or a renal artery bruit.

• Worsening renal function with ACEI
• Disparity on renal size on USS > 1.5 cm (Ischaemic nephropathy)
• Flash pulmonary oedema
• Neurofibromatosis I (also get phaeochromocytomas)
• Renal bruit
• Intermittent claudication suggesting coexisting atherosclerosis + hypertension
• Proteinuria

Tests

• Captopril enhanced radionuclide renal scan: shows reduced uptake on the affected side which may be exacerbated by Aspirin or captopril
• MR Angiography with gadolinium enhancement shows a string of beads in Fibromuscular dysplasia and focal narrowing with atherosclerosis
• Spiral CTA with contrast less expensive than MRA
• Duplex doppler scan can assist renal artery flow velocity
• Intra-arterial angiography: the gold standard – should be carried out by experienced radiologists with minimal contrast load.

Indications for interventions

• Stenosis> 75%
• Flash pulmonary oedema
• Resistant hypertension
• Affecting solitary kidney

Management

• Treat Pulmonary oedema. Avoid ACEI/AT2 blockers. Use Furosemide, Nitrates. Also consider low-dose dopamine for its natriuretic effect if no response to initial therapy.
• Best Medical - Aspirin, statins, BP meds, Calcium channel blockers, Diuretics to optimise blood pressure and atheroma
• Transluminal Angioplasty +/- stents but risks appear higher in those with Fibromuscular dysplasia
• Surgical resection of a stenosed portion of the artery
• Nephrectomy may be required
• Blood pressure improves but rarely returns to normal after treatment for atherosclerotic RAS. A lot depends on patient selection as at post mortem studies some degree of RAS is often seen in those with atherosclerosis and hypertension but may not be causative.