What are the causes of renal artery aneurysm?

Causes of Renal Artery Aneurysm

Renal artery aneurysms are most commonly caused by atherosclerotic degeneration (approximately 75% of cases), followed by fibromuscular dysplasia (approximately 21%), with rare causes including connective tissue disorders, vasculitis, infection, and trauma. 1, 2

Primary Etiologies

Atherosclerotic Degeneration (Most Common)

• Atherosclerosis accounts for approximately 75% of all renal artery aneurysms, typically occurring in older patients with systemic atherosclerotic disease 2
• These aneurysms most commonly present as congenital saccular aneurysms that undergo secondary atherosclerotic degeneration over time 3
• The mean age at presentation is approximately 58 years, with a strong association with traditional cardiovascular risk factors 2
• Atherosclerotic aneurysms tend to involve the main renal artery (52% of cases) or primary branches (44%), with the remainder being intraparenchymal 2

Fibromuscular Dysplasia (Second Most Common)

• Fibromuscular dysplasia causes approximately 21% of renal artery aneurysms and represents a nonatherosclerotic, noninflammatory arteriopathy 1, 2
• FMD predominantly affects young to middle-aged women (ages 25-50 years), though it can occur in both genders at any age 1, 4, 5
• Medial fibroplasia accounts for 80-85% of FMD cases and characteristically involves the middle and distal two-thirds of the main renal artery, unlike atherosclerotic disease which affects proximal segments 1, 5
• Fusiform aneurysmal dilatation typically occurs distal to focal fibromuscular dysplastic stenosis 3
• The classic "string of beads" angiographic appearance may coexist with aneurysmal changes 4, 5
• FMD-associated aneurysms reflect a systemic arteriopathy, with increased prevalence of intracranial aneurysms in women with renal artery aneurysms 6

Connective Tissue Disorders

• Ehlers-Danlos syndrome accounts for approximately 4% of renal artery aneurysms due to underlying collagen abnormalities 1, 2
• Other hereditary disorders affecting arterial wall integrity include Marfan syndrome and neurofibromatosis 1

Infectious/Inflammatory Causes

• Mycotic aneurysms can develop from bacteremic seeding of the arterial wall, particularly in immunocompromised patients such as renal transplant recipients 1
• Among 640 renal transplant recipients, 1% developed mycotic aneurysms related to perinephric infections 1
• Takayasu's arteritis represents a rare inflammatory cause of renal artery aneurysms 1

Traumatic and Iatrogenic Causes

• Direct trauma, lithotripsy, surgical injury, and prior abdominal radiation therapy can all lead to aneurysm formation 1
• Spontaneous renal artery dissection may result in dissecting aneurysms, which are particularly damaging and prone to branch thrombosis and renal infarction 3

Rare Causes

• Williams syndrome and arteriovenous malformations or fistulas represent uncommon etiologies 1
• Atheroemboli and thromboemboli can contribute to aneurysm formation 1
• Retroperitoneal fibrosis producing external compression has rarely been associated with renal artery disease 1

Clinical Pitfalls and Important Considerations

Women comprise 72% of those affected by renal artery aneurysms, with particular concern for rupture risk in premenopausal women and during pregnancy 7, 2

Noncalcified aneurysms larger than 2 cm in diameter carry the highest rupture risk, especially in premenopausal women due to increased risk during pregnancy 1, 4

The natural history varies by etiology: atherosclerotic aneurysms typically remain stable if well-calcified and small, whereas FMD-associated aneurysms may be part of a progressive systemic arteriopathy requiring surveillance of multiple vascular beds 4, 2, 6

Approximately 39% of renal artery aneurysms are discovered incidentally, 39% during evaluation for hypertension, and only 7% present with symptoms directly attributable to the aneurysm 2

When evaluating young women with renal artery aneurysms, consider screening for intracranial aneurysms, as these may occur with greater frequency than in the general population, reflecting an underlying systemic arteriopathy 4, 6