Diagnostic Ultrasound - Abdomen and Pelvis

Renal Artery Stenosis
514
Diagnoses: Urinary Tract
PATHOLOGY
General Features
• Etiology
○ Atherosclerosis
– Ostium (aortic plaque) or proximal 2 cm of renal artery
– RAS bilateral in 30-40% of atherosclerosis cases
○ FMD
– Medial fibroplasia 70-80% FMD; intimal hyperplasia:
10-15%; subadventitial fibroplasia 10-15%
– Most common mid or distal main renal artery ± hilar
branches
– Right RA > left; bilateral 2/3 of cases
○ Aortic dissection
○ Aortic aneurysm (renal artery compression)
○ Thromboembolism (more likely leads to occlusion than
renal artery stenosis)
○ Other vasculitides (e.g., Takayasu, polyarteritis nodosa,
congenital intimal fibroplasia)
○ Retroperitoneal fibrosis
○ Trauma with renal artery dissection
Staging, Grading, & Classification
• Hemodynamically significant arterial stenosis:
Pressure/flow reducing lesion
• Hemodynamically significant RAS: ≥ 50-60% diameter
reduction
Gross Pathologic & Surgical Features
• Atherosclerosis
○ Eccentric or circumferential plaque in proximal RA
○ Possible turbulence-related poststenotic dilatation
• Medial fibroplasia FMD
○ String of beads appearance
• Renal parenchymal atrophy (renal length ≤ 8 cm)
moderate/severe RAS
Microscopic Features
• Atherosclerotic plaque: Subintimal fibrofatty plaque,
possibly calcified
• Medial fibroplasia FMD: Fibrous ridges with intervening
media thinning/aneurysmal dilatation
CLINICAL ISSUES
Presentation
• Most common signs/symptoms
○ No signs or symptoms specific for RA hypertension
○ Clinical scenarios suggesting RA hypertension and
justifying RA imaging
– Hypertension in child or young adult
– Hypertension uncontrolled with 3 or more drugs
– Previously controlled hypertension newly
uncontrollable
– Rapidly worsening (malignant) hypertension
– Hypertension with deteriorating renal function
• Other signs/symptoms
○ Unilateral small kidney
Demographics
• Age
○ Atherosclerosis: > age 50 years
○ FMD: Usually young adulthood
• Gender
○ Atherosclerosis: Male predominance
○ FMD: Female predominance
• Epidemiology
○ RAS most common cause of secondary hypertension (1-
4% of all HTN)
– Called "renovascular hypertension"
○ Atherosclerosis
– Most common cause of RAS (60-90% of cases)
○ FMD
– 2nd most common cause of RAS overall (10-30%
cases)
– Most common cause of renovascular hypertension in
children and young adults
Natural History & Prognosis
• Atherosclerosis: Poor prognosis after RAS
angioplasty/surgery
○ Mixed results for hypertension control, poor results for
arresting decline in renal function
– Debate continues about role of stents vs. angioplasty
○ Impossible to predict who is likely to respond, visually
successful treatment not always associated with clinical
improvement
• FMD: Good prognosis after RAS angioplasty
○ Hypertension improved or medically controllable
○ Recurrent stenosis possible
Treatment
• Angiotensin converting enzyme (ACE) inhibitors
• Transluminal angioplasty: 80% RAS correction rate for
nonostial lesions; 25-30% ostial
• Surgical revascularization: 80-90% success rate (bypass
stenosis)
DIAGNOSTIC CHECKLIST
Consider
• RAS/RA occlusion with unilateral small kidney
Image Interpretation Pearls
• Atherosclerotic RAS: Proximal 2 cm of RA
• FMD-RAS: Mid or distal RA ± intrarenal branches and string
of beads appearance
SELECTED REFERENCES
1. Albert TS et al: An international multicenter comparison of time-SLIP
unenhanced MR angiography and contrast-enhanced CT angiography for
assessing renal artery stenosis: the renal artery contrast-free trial. AJR Am J
Roentgenol. 204(1):182-8, 2015
2. Chrysant GS et al: Proper patient selection yields significant and sustained
reduction in systolic blood pressure following renal artery stenting in
patients with uncontrolled hypertension: long-term results from the
HERCULES trial. J Clin Hypertens (Greenwich). 16(7):497-503, 2014
3. Voiculescu A et al: Duplex ultrasound findings before and after surgery in
children and adolescents with renovascular hypertension. Ultrasound Med
Biol. 40(12):2786-93, 2014
4. Granata A et al: Doppler ultrasound and renal artery stenosis: An overview. J
Ultrasound. 12(4):133-43, 2009