Renovascular Hypertension

• The Renin-Angiotensin-Aldosterone System (RAAS) Activation: Stenosis of the renal artery reduces hydrostatic pressure at the afferent arteriole, which is sensed by baroreceptors in the juxtaglomerular apparatus. This triggers renin release from granular cells of the afferent arteriole. Renin cleaves angiotensinogen (synthesized in the liver) to form angiotensin I (Ang I). The angiotensin-converting enzyme (ACE), primarily located on pulmonary endothelium, converts Ang I to the potent vasoconstrictor angiotensin II (Ang II). Ang II acts through the AT1 receptor to cause: (1) direct systemic vasoconstriction increasing peripheral vascular resistance; (2) stimulation of aldosterone synthesis and release from the zona glomerulosa, which promotes sodium reabsorption in the collecting duct and expands intravascular volume; and (3) increased sympathetic nervous system activity. These mechanisms together produce the characteristic two-kidney, one-artery model pattern where the stenotic kidney maintains hypertension through RAAS activation while the contralateral kidney is exposed to systemic hypertension. In unilateral RVH, the contralateral kidney experiences pressure natriuresis, partially offsetting sodium retention; however, in bilateral RVH or RVH with solitary kidney, both kidneys are involved in sodium retention, leading to volume-dependent hypertension refractory to ACE inhibitors or ARBs and predisposing to flash pulmonary edema.

• Atherosclerotic Renal Artery Stenosis (ARAS) Mechanism: ARAS develops through the same atherosclerotic plaque formation affecting coronary and cerebral vessels, typically at the ostium or proximal third of the renal artery. Atherosclerotic plaques are composed of lipid-laden macrophages, smooth muscle cells, and connective tissue. Rupture of unstable plaques with thrombotic occlusion can cause acute worsening of stenosis or complete occlusion. ARAS is strongly associated with smoking, dyslipidemia, diabetes mellitus, and male gender. The pathology is progressive, with hemodynamically significant stenosis (>60% diameter narrowing; >75% area stenosis) developing over months to years. ARAS frequently occurs in patients with established atherosclerotic disease (coronary artery disease, peripheral arterial disease, cerebrovascular disease), and approximately 20-30% of patients undergoing coronary angiography for CAD have incidental renal artery stenosis.

• Fibromuscular Dysplasia (FMD) Mechanism: FMD is a non-atherosclerotic, non-inflammatory vasculopathy characterized by dysplasia of the medial, intimal, or adventitial layers of medium-sized arteries. The medial form (medial fibroplasia), accounting for ~60% of FMD cases, produces the classic "string of beads" appearance on angiography due to alternating areas of stenosis and microaneurysm formation. The adventitial form produces concentric, proliferative lesions. The intimal form produces focal stenosis. The etiology of FMD remains incompletely understood but likely involves developmental anomalies with genetic predisposition (familial clustering reported in 8-10% of cases), abnormal alpha-smooth muscle actin expression, altered mechanotransduction, and possible estrogen-receptor signaling abnormalities (explaining female predominance). Unlike ARAS, FMD is not associated with systemic atherosclerosis and progresses more slowly; however, FMD patients have increased risk of arterial dissection, coronary artery FMD, and aneurysms.

• Progressive Renal Damage and Azotemia: In addition to hypertension, renal artery stenosis causes direct renal damage through hypoperfusion-induced tubular atrophy, glomerulosclerosis, and interstitial fibrosis. With unilateral stenosis, glomerular filtration rate (GFR) remains relatively preserved due to the contralateral kidney's compensatory hyperfiltration. However, with bilateral stenosis or stenosis of a solitary kidney, renal function deteriorates progressively. This ischemic nephropathy is accelerated by the use of ACE inhibitors or ARBs, which block Ang II-mediated preferential efferent arteriolar vasoconstriction—in the stenotic kidney, this preferential efferent vasodilation causes glomerular pressure to drop precipitously, reducing GFN further. The "ischemic penumbra" concept describes renal tissue that remains perfused but is at risk for progression to infarction and fibrosis. ACE inhibitor-induced acute kidney injury in the setting of renal artery stenosis (typically a rise in serum creatinine >30% within days of initiation) is a classic board scenario reflecting this mechanism.

• Atherosclerotic Renal Artery Stenosis (ARAS) — accounts for 80-90% of RVH cases. Major risk factors include age >50 years, male gender, smoking (current or former), hypertension, dyslipidemia, diabetes mellitus, obesity, and chronic kidney disease. ARAS frequently coexists with CAD, stroke, or peripheral arterial disease. The diagnosis of ARAS should be strongly considered in patients with: (1) new-onset hypertension after age 50, (2) resistant hypertension (blood pressure inadequately controlled on ≥3 antihypertensive agents), (3) accelerated or malignant hypertension, (4) acute rise in serum creatinine following ACE inhibitor/ARB initiation, (5) flash pulmonary edema with preserved ejection fraction, or (6) abdominal or flank bruits on examination. Progressive ARAS can lead to total occlusion of the renal artery, which paradoxically may result in normalization of blood pressure if the kidney becomes totally non-functional and no longer contributes to RAAS activation.

• Fibromuscular Dysplasia (FMD) — accounts for 10-20% of RVH, predominantly affecting young to middle-aged women (female-to-male ratio approximately 4-5:1). FMD frequently involves the renal arteries but also commonly affects the carotid and vertebral arteries (increasing stroke risk), coronary arteries, and iliac arteries. FMD should be suspected in young, otherwise healthy patients (<50 years) with new-onset hypertension without traditional atherosclerotic risk factors, particularly if female. The pathophysiology involves medial layer dysplasia creating the characteristic angiographic appearance. FMD can be associated with connective tissue disorders, though most FMD patients have no identified syndromic features. The inheritance pattern suggests possible autosomal dominant transmission with incomplete penetrance, though most cases are sporadic.

• Other Etiologies (rare, <10% of RVH cases):
• Takayasu's arteritis — large-vessel vasculitis affecting the aorta and its branches, causing ostial renal artery stenosis; predominantly affects young women in Asia and developing countries; often presents with systemic symptoms and elevated inflammatory markers
• Thromboembolism — acute renal artery thrombosis from cardiac embolism or in-situ thrombosis, causing acute flank pain and acute hypertension
• Renal artery dissection — spontaneous or secondary to trauma; particularly common in FMD patients
• Neurofibromatosis type 1 — dysplasia of renal artery medial layer; associated with pheochromocytoma as well
• Aortic dissection — compromising renal artery origin
• Extrinsic compression — tumors or retroperitoneal fibrosis compressing renal arteries

• Hypertension (Universal Finding) — all RVH patients present with elevated blood pressure. The hypertension may be newly diagnosed, resistant to medical therapy, or accelerated. In FMD, hypertension onset is typically abrupt in young patients. In ARAS, hypertension may develop insidiously over months to years. The mechanism reflects RAAS activation as described above. Malignant hypertension (systolic BP >180 mmHg with end-organ damage) can occur with either ARAS or FMD.

• Flank or Abdominal Bruit — presence of an abdominal bruit (systolic or systolic-diastolic) on careful auscultation between the umbilicus and anterior superior iliac spine is suggestive of renal artery stenosis, particularly when present in a young patient or with resistant hypertension. However, the absence of a bruit does not exclude RVH. The bruit results from turbulent flow through the stenotic renal artery. Sensitivity and specificity vary widely depending on clinician skill and operator-dependent factors but are generally modest (sensitivity ~40-50%, specificity ~70%).

• Acute Kidney Injury After ACE Inhibitor or ARB Initiation — development of acute rise in serum creatinine of >30% or absolute rise >0.3 mg/dL within days to 2 weeks of starting an ACE inhibitor or ARB is a hallmark of bilateral RVH or RVH of a solitary kidney. This occurs because ACE inhibitors and ARBs block Ang II-mediated preferential efferent arteriolar vasoconstriction; in stenotic kidneys where glomerular filtration is already critically dependent on efferent arteriolar tone, this leads to precipitous decline in GFR. This is one of the most highly tested phenomena for USMLE Step 2 CK and should prompt immediate discontinuation of the offending agent and investigation for RVH.

• Flash Pulmonary Edema (Acute Decompensation) — patients with bilateral RVH or RVH of a solitary kidney present with acute, severe hypertension and flash pulmonary edema (acute dyspnea, orthopnea, pulmonary rales) with preserved ejection fraction and normal cardiac output. This represents acute volume overload from severe sodium and water retention driven by RAAS activation in the setting of hypertension. These patients are often initially misdiagnosed with acute decompensated heart failure due to preserved ejection fraction. The distinction is critical because standard heart failure therapy (ACE inhibitors, ARBs, diuretics) may be insufficient or counterproductive; revascularization of the stenotic artery(ies) is often definitive.

• Progressive Renal Insufficiency — patients may present with gradual decline in renal function (rising serum creatinine, falling GFR) reflecting ischemic nephropathy. With unilateral RVH, renal function decline is often modest and attributed to age or other causes. With bilateral RVH or RVH of a solitary kidney, renal function may decline rapidly, and patients may progress to end-stage renal disease (ESRD) requiring dialysis.

• Symptoms of Hypertensive End-Organ Damage:
• Headache, visual changes, neurologic symptoms suggesting hypertensive encephalopathy or posterior reversible encephalopathy syndrome (PRES)
• Chest pain or dyspnea from myocardial ischemia or infarction, or flash pulmonary edema
• Hematuria or proteinuria detected on urinalysis, reflecting glomerular disease from hypertension or underlying renal artery stenosis

• Physical Examination Findings (beyond blood pressure elevation):
• Abdominal or flank bruit — best heard with patient supine, listening laterally; suggests turbulent flow through stenotic artery
• Signs of hypertensive crisis: fundoscopic changes (papilledema, retinal hemorrhages, cotton-wool spots, microinfarcts), indicating hypertensive retinopathy
• Signs of congestive heart failure: elevated jugular venous pressure, peripheral edema, pulmonary rales (particularly in flash pulmonary edema with preserved ejection fraction)
• Focal neurologic deficits if stroke has occurred

• Important Clinical Variants:
• "Flash pulmonary edema RVH" — acute, life-threatening presentation with severe hypertension and acute dyspnea, predominantly in bilateral RVH or RVH of solitary kidney; represents a medical emergency
• "Incidental RVH" — renal artery stenosis discovered on imaging (CT, MRI, or angiography) obtained for other indications in asymptomatic or minimally symptomatic patients; common in patients undergoing coronary angiography
• "Asymptomatic RVH" — stenosis without hypertension (rare; <5% of RVH cases); may represent hemodynamically insignificant stenosis or early disease

• Clinical Scoring and Risk Stratification — The "Captopril Renography Scan Positive Criteria" (now largely historical due to superior imaging modalities) included at least 2 of: (1) systolic BP >160 mmHg, (2) hypokalemia (K <3.5 mEq/L), (3) azotemia (serum creatinine >1.5 mg/dL), (4) >30% rise in serum creatinine after ACE inhibitor/ARB. Modern "High-Risk Features for RVH" include: (1) age <50 years (suggests FMD), (2) age >50 with smoking history (suggests ARAS), (3) resistant hypertension (BP inadequately controlled on ≥3 agents), (4) accelerated or malignant hypertension, (5) acute kidney injury with ACE-I/ARB, (6) flash pulmonary edema with preserved ejection fraction, (7) abdominal bruit, (8) prior atherosclerotic disease (CAD, stroke, PAD). Patients with multiple high-risk features warrant imaging workup.

• Renal Artery Duplex Ultrasonography — First-line imaging modality in many centers due to availability, lack of radiation, no contrast, and operator-dependence minimal with experienced sonographers. Uses B-mode imaging to visualize renal artery anatomy and color/spectral Doppler to measure flow velocities. Peak systolic velocity (PSV) thresholds for >60% stenosis: PSV >200 cm/sec (some centers use >180 cm/sec) and renal artery-to-aortic (RAR) ratio >3.5 (peak systolic velocity of renal artery divided by abdominal aortic PSV). Renal resistive index (RI) measured as (peak systolic velocity - end-diastolic velocity)/peak systolic velocity; RI >0.8 may predict poor response to revascularization. Sensitivity and specificity for >60% stenosis: 85-98% sensitivity, 85-95% specificity (highly dependent on operator and patient factors; limited in

Immediate stabilisation (flash pulmonary edema or hypertensive emergency)

• Airway/oxygenation: noninvasive positive-pressure ventilation reduces preload and work of breathing in flash pulmonary edema.
• IV vasodilators titratable minute-to-minute: for flash pulmonary edema, the ACC/AHA 2017 Hypertension Guideline favors clevidipine, nitroglycerin, or nitroprusside; nicardipine is an alternative. Beta blockers (labetalol, esmolol) are avoided in acute pulmonary edema because of negative inotropy — reserve IV labetalol for hypertensive emergencies without pulmonary edema. In either scenario lower mean arterial pressure by no more than ~25% in the first hour to avoid renal and cerebral hypoperfusion across a fixed stenosis.
• Loop diuretic (furosemide) for the volume-dependent sodium retention of bilateral disease. Persistent or recurrent flash pulmonary edema is an accepted indication for urgent revascularisation.

First-line chronic therapy — medical

• RAAS blockade: ACE inhibitor (lisinopril) or ARB (losartan) is the most mechanistically rational agent in unilateral stenosis because angiotensin II drives the hypertension; the ACC/AHA hypertension guideline supports RAAS blockade with creatinine and potassium rechecked within 1–2 weeks. A rise in creatinine >30% mandates withdrawal and evaluation for bilateral disease.
• Add-on agents: dihydropyridine CCB (amlodipine) and thiazide-type diuretic (chlorthalidone) are the usual second and third drugs; beta blockers blunt renin release from the juxtaglomerular apparatus.
• Atherosclerotic risk-factor control (ARAS): high-intensity statin per the ACC/AHA cholesterol guideline, antiplatelet therapy, smoking cessation, and glycemic control — this is disease-modifying, not adjunctive.

Revascularisation

• FMD: percutaneous transluminal angioplasty without stenting is the procedure of choice and is frequently curative in young patients with short disease duration (First International Consensus on FMD).
• ARAS: stenting is reserved for failure of maximal medical therapy — recurrent flash pulmonary edema, truly refractory hypertension, or progressive/rapid loss of GFR — because CORAL and ASTRAL showed no benefit of routine stenting added to medical therapy.
• Surgical bypass/endarterectomy: for complex ostial or aneurysmal anatomy, or failed endovascular therapy.

Contraindicated/avoid

• ACEI/ARB in bilateral stenosis or stenosis of a solitary kidney — a relative contraindication: avoid, or initiate only with close monitoring using the 1–2 week creatinine/potassium recheck above, and discontinue for a >30% creatinine rise. Efferent arteriolar dilation collapses filtration pressure.
• All ACE inhibitors and ARBs in pregnancy (fetotoxic); captopril's short half-life makes it useful for rapid titration, not for pregnant patients.
• Beta blockers as the parenteral agent in acute pulmonary edema; NSAIDs (afferent constriction) and avoidable iodinated contrast loads in advanced CKD.

Complications of the disease

• Ischemic nephropathy progressing to ESRD: chronic hypoperfusion causes tubular atrophy, interstitial fibrosis and glomerulosclerosis. Signalled by a slowly rising creatinine with bland urine sediment and, on imaging, asymmetric kidney size (the stenotic kidney atrophies, often >1.5 cm smaller).
• Flash pulmonary edema: RAAS-driven sodium and water retention plus impaired pressure natriuresis in bilateral disease. Abrupt dyspnea and rales with preserved ejection fraction. Emergency.
• Hypertensive emergency/malignant hypertension: sustained angiotensin II vasoconstriction produces fibrinoid necrosis of arterioles. Look for papilledema, retinal hemorrhages, encephalopathy, or schistocytes with thrombocytopenia (hypertensive thrombotic microangiopathy). Emergency.
• Secondary hyperaldosteronism: hypokalemia with metabolic alkalosis in the setting of high plasma renin activity — the biochemical mirror image of primary aldosteronism.
• Cardiovascular end-organ injury: LVH, diastolic heart failure, stroke, and accelerated atherosclerosis elsewhere.
• Acute renal infarction: plaque rupture with thrombosis, or dissection in FMD — sudden flank pain, hematuria, markedly elevated LDH, wedge-shaped perfusion defect on CT. Emergency.
• FMD-specific: arterial dissection (renal, carotid/vertebral, coronary — SCAD) and aneurysm formation with risk of rupture; a new headache, neck pain, or pulsatile tinnitus in a young woman with renal FMD demands cerebrovascular imaging.

Complications of treatment

• ACEI/ARB-induced AKI: efferent arteriolar dilation drops transcapillary filtration pressure. Creatinine rise >30% within days of starting the drug; usually reversible on withdrawal.
• Hyperkalemia from RAAS blockade, compounded by reduced GFR.
• Contrast-associated AKI after CTA or catheter angiography — the attributable risk with modern low-osmolar and iso-osmolar agents is substantially lower than historically taught, and post-catheterization renal decline should be distinguished from atheroembolic injury, which is subacute and stepwise rather than occurring within the first days.
• Atheroembolic (cholesterol crystal) disease after catheter manipulation: livedo reticularis, blue toe syndrome, eosinophilia/eosinophiluria, hypocomplementemia, subacute stepwise renal decline.
• Procedural: renal artery dissection, perforation, thrombosis, in-stent restenosis, and access-site hematoma or pseudoaneurysm.

• Two demographic archetypes: a young woman with abrupt severe hypertension and a string of beads in the mid-to-distal renal artery equals fibromuscular dysplasia; an older smoker with known atherosclerosis and an ostial/proximal lesion equals atherosclerotic renal artery stenosis. Lesion location is the discriminator examiners love.
• The single most tested trigger: a creatinine jump of more than ~30% within days of starting an ACE inhibitor or ARB. Best next step is to stop the drug and image the renal arteries — this pattern implies bilateral stenosis or stenosis in a solitary kidney.
• Flash pulmonary edema with preserved EF plus resistant hypertension (Pickering syndrome) is bilateral RAS until proven otherwise and is one of the few accepted indications for revascularisation in ARAS.
• Best initial test in most stems: renal artery duplex ultrasound (or CTA/MRA if body habitus limits it); catheter angiography remains the gold standard and is reserved for when intervention is planned.
• Distractor to avoid — primary aldosteronism: both give hypertension, hypokalemia and metabolic alkalosis, but RVH has high renin with high aldosterone, whereas primary aldosteronism has suppressed renin. Check the aldosterone-to-renin ratio before committing.
• CORAL and ASTRAL: routine stenting of atherosclerotic lesions does not beat optimal medical therapy. Medical therapy — RAAS blockade, statin, antiplatelet, smoking cessation — is the answer unless the stem gives refractory hypertension, flash pulmonary edema, or falling GFR.
• FMD is treated with balloon angioplasty alone, no stent, and can cure the hypertension; every FMD patient warrants one-time head-to-pelvis arterial imaging for extrarenal FMD, aneurysm, and dissection (First International Consensus on FMD).
• Never choose an ACE inhibitor or ARB in a pregnant patient — all are fetotoxic, captopril included.