Renal Artery Aneurysm

A renal artery aneurysm is a focal dilatation of the main renal artery or its branches, usually at a bifurcation. It is found in about 0.1 to 1% of angiograms.

About 90% are saccular, and about 10% are intrarenal. Fusiform aneurysms usually follow fibromuscular dysplasia or post-stenotic dilatation.

Causes are atherosclerosis, fibromuscular dysplasia (especially in women), polyarteritis nodosa and other vasculitis, Ehlers-Danlos syndrome, trauma, pregnancy and dissection.

Rupture is uncommon, but when it occurs in pregnancy maternal and foetal mortality are high.

Pathophysiology. Medial weakening, abnormal flow at the bifurcation and hormonal changes in pregnancy cause saccular dilatation.

Hypertension arises from renin release when flow is disturbed, from a coexisting renal artery stenosis, or from distal embolisation. Thrombus in the sac can embolise to the kidney.

• Asymptomatic in most. Found on imaging.
• Hypertension, often resistant or of early onset, and a bruit over the flank.
• Flank pain, haematuria and renal infarction from thrombus or embolisation.
• Rupture: sudden flank pain, haematuria and shock. Arteriovenous fistula can cause high output heart failure.
• Features of the cause: fibromuscular dysplasia, systemic vasculitis, or a connective tissue syndrome.

• Duplex ultrasound for the renal artery and kidney size and flow.
• CT angiography. Size, number, neck, calcification, thrombus, branch involvement and relation to the pelvis and vein. MR angiography is an alternative, avoiding gadolinium at eGFR under 30 mL/min/1.73 m2 unless a macrocyclic agent is chosen.
• Catheter angiography before intervention, with renal vein renin sampling when a link to hypertension is unclear.
• Laboratory. Creatinine and eGFR, urinalysis, potassium, plasma renin and aldosterone when hypertension is present.
• Cause workup. Imaging of the head, neck, abdomen and pelvis for fibromuscular dysplasia, CRP, ESR and ANCA, and genetic testing when a connective tissue disorder is suspected.

Differential diagnosis.

• Renal artery stenosis with post-stenotic dilatation
• Fibromuscular dysplasia with the string-of-beads appearance
• Renal arteriovenous malformation or fistula
• Renal cyst, renal cell carcinoma and adrenal mass
• Renal artery dissection
• Polyarteritis nodosa microaneurysms
• Calcified lymph node or hydronephrosis

Indications for treatment. Diameter of 20 mm or more (30 mm in older men and postmenopausal women with low risk), any size in women of childbearing age or who plan pregnancy, symptoms, hypertension attributable to the aneurysm, growth of 5 mm or more in a year, thrombus with embolisation, dissection, arteriovenous fistula, and rupture.

Surveillance. Asymptomatic aneurysm under 20 mm: imaging every 12 months for the first 2 years, then every 2 years.

Blood pressure.

• Target under 130/80 mm Hg.
• Amlodipine 5 mg orally once daily, increased to 10 mg (maximum 10 mg daily, start 2.5 mg in older adults and liver impairment).
• Ramipril 2.5 mg orally once daily, increased every 2 to 4 weeks to 10 mg once daily (maximum 10 mg daily, and 5 mg daily at creatinine clearance under 30 mL/min), with potassium and creatinine 1 to 2 weeks after each change. Contraindicated in pregnancy and bilateral renal artery stenosis.
• Bisoprolol 2.5 mg orally once daily, increased to 5 to 10 mg once daily, maximum 20 mg daily (do not exceed 10 mg daily at creatinine clearance under 20 mL/min or in severe liver impairment), as an additional drug, because it lowers wall stress.

Interventions.

• Endovascular: coil embolisation of saccular aneurysms with a narrow neck, covered stents, stent assisted coiling or flow diverters. Risks are renal infarction, rupture, coil migration and contrast nephropathy.
• Open surgery: aneurysmectomy with patch angioplasty, resection with end-to-end anastomosis, or bypass, and ex vivo repair with autotransplantation for complex branch aneurysms. Nephrectomy is a last resort.
• After a covered stent or reconstruction: aspirin 75 to 100 mg once daily, with clopidogrel 75 mg for 1 to 3 months after a stent.
• Rupture: emergency embolisation or surgery, resuscitation with blood, nephrectomy when haemostasis fails.

Special groups.

• Pregnancy: repair before conception for aneurysms of 15 mm or more or any size with risk factors. During pregnancy, control blood pressure with labetalol, modified release nifedipine or methyldopa, and treat by endovascular means or surgery for rupture risk, with obstetric support. Avoid ramipril.
• Fibromuscular dysplasia: screen the other vascular beds, and avoid heavy straining and cervical manipulation.
• Vasculitis: prednisolone 1 mg/kg orally once daily (maximum 60 mg) with a taper and a steroid sparing drug chosen with rheumatology.

Monitoring. Imaging at 1 month and 6 months after intervention, then yearly. Blood pressure at each visit, with creatinine and potassium after any change in renin angiotensin drugs.

Referral and escalation. Refer to vascular surgery or interventional radiology, and to nephrology for hypertension or impaired renal function. Emergency for rupture, or any aneurysm found in pregnancy.