Residency · Residency · Nephrology

Hypertensive Nephrosclerosis and Renovascular Disease

Introduction

Hypertensive nephrosclerosis is the second leading cause of end-stage renal disease in the United States, accounting for approximately 25 percent of incident ESRD. The disease disproportionately affects African Americans, in whom APOL1 risk variants contribute significantly to the excess burden of hypertension-attributed CKD and ESRD. Renovascular disease encompasses two distinct entities: atherosclerotic renal artery stenosis and fibromuscular dysplasia, each with different pathophysiology, demographics, and management approaches. Understanding the spectrum of hypertensive kidney injury is critical for appropriate diagnosis and management.

Hypertensive Nephrosclerosis

Benign Nephrosclerosis

Benign nephrosclerosis represents the chronic, slowly progressive kidney disease resulting from longstanding hypertension. The pathologic hallmarks include arteriolar hyalinosis of the afferent arteriole, intimal fibrosis of the interlobular arteries, global glomerulosclerosis of the ischemic type characterized by wrinkling and collapse of the capillary tuft, tubular atrophy, and interstitial fibrosis. The clinical presentation is characterized by slowly progressive CKD with mild proteinuria typically less than 1 gram per day, a bland urine sediment, and longstanding hypertension. Benign nephrosclerosis remains a diagnosis of exclusion, requiring the clinician to rule out other causes of CKD including diabetic nephropathy, chronic glomerulonephritis, and reflux nephropathy. Importantly, APOL1-mediated nephrosclerosis, driven by homozygous or compound heterozygous G1/G2 risk variants, is now recognized as a distinct entity from traditional benign nephrosclerosis and represents a significant contributor to the excess CKD burden in African Americans.

Malignant Nephrosclerosis

Malignant nephrosclerosis results from acute, severe hypertension, typically with blood pressures exceeding 180/120 mmHg accompanied by end-organ damage. The pathologic findings are distinct from benign nephrosclerosis and include fibrinoid necrosis of the arterioles and "onion skinning" of the interlobular arteries resulting from concentric mucoid intimal hyperplasia, along with features of thrombotic microangiopathy. The clinical presentation includes acute kidney injury, proteinuria that can reach nephrotic range, hematuria, schistocytes on peripheral blood smear, and elevated lactate dehydrogenase. Malignant hypertension is associated with uncontrolled essential hypertension, scleroderma renal crisis, cocaine use, pheochromocytoma, and preeclampsia. Treatment requires controlled blood pressure reduction, targeting a 25 percent reduction in mean arterial pressure over the first 24 hours while avoiding precipitous drops that risk watershed infarction, particularly cerebral and renal. Intravenous antihypertensives including nicardipine, clevidipine, nitroprusside for short-term use, fenoldopam, and labetalol are the agents of choice. Immediate normalization of blood pressure should be avoided.

APOL1-Associated Kidney Disease

APOL1 G1 and G2 risk variants on chromosome 22 are present in approximately 13 percent of African Americans in the homozygous or compound heterozygous state. These variants confer an evolutionary advantage by providing protection against Trypanosoma brucei rhodesiense, the parasite responsible for East African sleeping sickness. The presence of two risk alleles dramatically increases the risk of multiple forms of kidney disease: FSGS risk is increased 17-fold, hypertensive ESRD risk 7 to 10-fold, and HIV-associated nephropathy risk 29-fold. APOL1 risk alleles are now understood to explain most of the excess CKD and ESRD burden in African Americans that was previously attributed to hypertension alone. The mechanism of APOL1-mediated kidney injury involves podocyte injury through ion channel or pore formation in the cell membrane, mitochondrial dysfunction, and impaired autophagy. For living kidney donation, APOL1 genotyping is recommended for African American potential donors using an FDA-approved test, as donors with two risk alleles face an increased long-term risk of kidney disease.

<image>Histopathology comparison showing three panels of hypertensive renal injury. Panel 1: Benign nephrosclerosis showing arteriolar hyalinosis with homogeneous eosinophilic material in the wall of the afferent arteriole, intimal fibrosis of an interlobular artery with concentric fibrous thickening, and a globally sclerosed glomerulus with wrinkling and collapse (ischemic pattern). Panel 2: Malignant nephrosclerosis showing fibrinoid necrosis of the arteriolar wall, "onion-skin" concentric mucoid intimal hyperplasia of an interlobular artery, thrombotic microangiopathy with fibrin thrombi in capillary lumens, and a glomerulus with mesangiolysis. Panel 3: APOL1-associated nephropathy showing collapsing FSGS pattern with podocyte hypertrophy/hyperplasia overlying a collapsed capillary tuft, and associated tubulointerstitial injury. Label all key histologic features.</image>

Renovascular Hypertension

Atherosclerotic Renal Artery Stenosis

Atherosclerotic renal artery stenosis is the most common cause of renovascular hypertension, accounting for more than 90 percent of cases. Its prevalence increases with age, affecting 7 percent of adults over 65 years and 15 to 30 percent of patients undergoing cardiac catheterization. The stenosis typically involves the ostium and proximal third of the renal artery, reflecting spill-over atherosclerosis from the aorta. Risk factors include age over 55, smoking, diabetes, dyslipidemia, and the presence of diffuse atherosclerotic disease including coronary artery disease, peripheral arterial disease, and carotid disease. Clinical consequences include resistant hypertension, ischemic nephropathy from chronic renal hypoperfusion leading to progressive CKD, and flash pulmonary edema in the setting of bilateral renal artery stenosis or unilateral stenosis in a solitary kidney.

Fibromuscular Dysplasia (FMD)

Fibromuscular dysplasia is a non-inflammatory, non-atherosclerotic vascular disease that primarily affects the renal and carotid/vertebral arteries. The most common subtype is medial fibroplasia, which produces the characteristic "string of beads" appearance on angiography and involves the mid-to-distal renal artery. FMD predominantly affects young to middle-aged women, who constitute 80 to 90 percent of cases. Other subtypes include intimal fibroplasia, which occurs in children and young adults, and adventitial fibroplasia, which is rare. FMD is associated with spontaneous coronary artery dissection and intracranial aneurysms, and screening with brain MRA is recommended. Treatment consists of percutaneous transluminal angioplasty without stenting, which achieves cure or improvement in 60 to 90 percent of patients.

Pathophysiology of Renovascular Hypertension

The Goldblatt model provides the physiologic framework for understanding renovascular hypertension. In the two-kidney, one-clip model representing unilateral renal artery stenosis, the ischemic kidney activates the renin-angiotensin-aldosterone system, generating angiotensin II that causes systemic vasoconstriction and sodium retention. The contralateral kidney initially undergoes pressure natriuresis to maintain volume homeostasis, but eventually volume expansion and hypertension predominate. The hypertension is initially angiotensin-dependent but later becomes volume-dependent. In the one-kidney, one-clip model representing bilateral RAS or unilateral stenosis in a solitary kidney, there is no contralateral kidney for pressure natriuresis, and volume-dependent hypertension develops from the outset, predisposing to flash pulmonary edema. Ischemic nephropathy results from progressive loss of renal parenchyma due to chronic hypoperfusion, manifesting as kidney atrophy and reduced cortical thickness. A stenosis is considered critical when it exceeds 70 percent luminal narrowing, with hemodynamic significance defined at greater than 50 percent stenosis with a trans-stenotic pressure gradient exceeding 20 mmHg.

Diagnosis

Clinical clues to renovascular hypertension include the onset of hypertension before age 30 (suggesting FMD) or after age 55 (suggesting atherosclerotic disease), resistant hypertension requiring three or more drugs, acute worsening of blood pressure on a previously stable regimen, flash pulmonary edema, a unilateral small kidney, acute kidney injury following ACE inhibitor or ARB initiation with a creatinine rise exceeding 30 percent, and an epigastric or renal artery bruit. Duplex ultrasonography is the first-line screening modality, with a peak systolic velocity above 200 cm/s indicating greater than 60 percent stenosis and a renal-to-aortic ratio above 3.5 supporting the diagnosis. Sensitivity is 85 to 95 percent but is operator-dependent. CT angiography provides excellent sensitivity and specificity of approximately 95 percent but requires iodinated contrast. MRA with gadolinium achieves a sensitivity of 90 to 95 percent, though gadolinium should be avoided at an eGFR below 30 due to the risk of nephrogenic systemic fibrosis with older linear agents; newer macrocyclic agents have a substantially improved safety profile. Catheter angiography remains the gold standard and allows simultaneous intervention, but is reserved for cases with high clinical suspicion and a plan to intervene.

<image>Angiographic comparison of atherosclerotic renal artery stenosis and fibromuscular dysplasia. Left panel: Atherosclerotic RAS showing a focal, eccentric stenosis at the ostium and proximal renal artery with post-stenotic dilation, aortic plaque extending into the renal artery origin. Include measurement markers showing >70% stenosis. Right panel: FMD showing the characteristic "string of beads" pattern in the mid-to-distal renal artery with alternating areas of stenosis and aneurysmal dilation (beads larger than the normal arterial diameter indicating medial fibroplasia). Include a small inset cross-section showing the histologic difference: atherosclerotic plaque with lipid core and fibrous cap versus FMD with alternating thinned and thickened medial fibromuscular ridges.</image>

Management of Atherosclerotic RAS

Medical Therapy (First-Line for Most Patients)

The CORAL trial, published in 2014, demonstrated definitively that renal artery stenting combined with optimal medical therapy was not superior to optimal medical therapy alone for preventing cardiovascular events, renal events, or death in patients with atherosclerotic renal artery stenosis. The ASTRAL trial, published in 2009, similarly showed that revascularization did not improve renal function, blood pressure control, cardiovascular events, or mortality. Optimal medical therapy consists of ACE inhibitor or ARB therapy, which is tolerated in unilateral RAS and reduces renin-driven hypertension (with creatinine monitoring), statin therapy, aspirin, blood pressure control to below 130/80, smoking cessation, and glycemic control. ACE inhibitors and ARBs are safe in unilateral RAS but contraindicated in bilateral RAS or unilateral stenosis in a solitary kidney, as they remove the efferent arteriolar tone needed to maintain GFR in the hypoperfused kidney.

Revascularization (Selected Cases)

Despite the negative results of CORAL and ASTRAL, revascularization remains appropriate for selected clinical scenarios that were underrepresented in these trials. Indications for consideration include flash pulmonary edema in the setting of bilateral RAS or a solitary kidney with RAS, refractory hypertension despite three or more drugs at adequate doses, progressive renal failure attributable to ischemic nephropathy with viable renal parenchyma, and recurrent acute decompensated heart failure. Primary stenting is the approach of choice for atherosclerotic RAS, as percutaneous angioplasty alone has a high restenosis rate due to elastic recoil. For FMD, angioplasty without stenting produces excellent results. Pre-procedural assessment of kidney viability should include a resistive index below 0.80 on Doppler ultrasonography, as an index above 0.80 predicts poor response to revascularization, along with a kidney length greater than 8 cm and cortical thickness greater than 1 cm.

Renal Artery Stenosis and RAAS Blockade

In unilateral RAS, ACE inhibitors and ARBs are generally well tolerated and effectively reduce angiotensin II-mediated hypertension. Serum creatinine should be monitored 1 to 2 weeks after initiation, with a rise exceeding 30 percent suggesting bilateral RAS or more severe stenosis than initially appreciated. In bilateral RAS or a solitary kidney with RAS, ACE inhibitors and ARBs are contraindicated because removing efferent arteriolar tone in the setting of severely reduced afferent perfusion pressure eliminates the compensatory mechanism maintaining glomerular filtration.

Cholesterol Crystal Embolization (Atheroembolic Disease)

Pathophysiology and Clinical Features

Cholesterol crystal embolization occurs when cholesterol crystals from ulcerated aortic plaques embolize to the renal and other organ vasculature. Common triggers include vascular procedures such as catheterization and surgery, anticoagulation therapy, and thrombolytic agents. The onset is typically days to weeks after the triggering event, distinguishing it temporally from contrast-induced nephropathy which occurs within 48 to 72 hours. The classic clinical triad consists of livedo reticularis, blue or purple toes known as "trash foot," and renal failure. Laboratory findings include eosinophilia, elevated erythrocyte sedimentation rate, low complement levels (C3 and C4), and elevated LDH. Renal biopsy demonstrates pathognomonic biconvex cleft-shaped spaces in the arcuate and interlobular arteries, representing cholesterol crystals that dissolved during tissue processing.

Management

Treatment of cholesterol crystal embolization is primarily supportive, as no specific therapy has been proven effective. Paradoxically, anticoagulation should be discontinued because it worsens embolization by exposing ulcerated plaque surfaces. Statin therapy is initiated for plaque stabilization. The prognosis is variable, with approximately 30 percent of patients requiring permanent dialysis and 30 percent achieving partial renal recovery.

Key Clinical Pearls

• CORAL and ASTRAL trials established that renal artery stenting for atherosclerotic RAS does not improve outcomes over optimal medical therapy for most patients
• Flash pulmonary edema with bilateral RAS remains a strong indication for revascularization despite negative trials (these patients were underrepresented in CORAL/ASTRAL)
• APOL1 risk variants, not hypertension per se, are the primary driver of CKD/ESRD risk in many African Americans historically diagnosed with "hypertensive nephrosclerosis"
• In malignant hypertension, reduce MAP by no more than 25% in the first 24 hours to avoid watershed organ ischemia
• Cholesterol crystal embolization is a clinical mimic of vasculitis (low complement, eosinophilia, multi-organ involvement) but has a distinctly different pathology and management

References

1. Cooper CJ, Murphy TP, Cutlip DE, et al. Stenting and Medical Therapy for Atherosclerotic Renal-Artery Stenosis (CORAL). N Engl J Med. 2014;370(1):13-22.
2. Wheatley K, Ives N, Gray R, et al. Revascularization versus Medical Therapy for Renal-Artery Stenosis (ASTRAL). N Engl J Med. 2009;361(20):1953-1962.
3. Gornik HL, Persu A, Adlam D, et al. First International Consensus on the Diagnosis and Management of Fibromuscular Dysplasia. Vasc Med. 2019;24(2):164-189.
4. Freedman BI, Limou S, Kopp JB. APOL1-Associated Nephropathy: A Key Contributor to Racial Disparities in CKD. Am J Kidney Dis. 2018;72(5 Suppl 1):S8-S16.
5. Textor SC. Ischemic Nephropathy: Where Are We Now? J Am Soc Nephrol. 2004;15(8):1974-1982.

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