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Short read · Renal & GU

Role of Nuclear Medicine in Renovascular Hypertension

Renal & GU · 3 min read

Renal artery stenosis is common and mostly incidental. Renovascular hypertension is the subset actually driving the blood pressure — the only subset revascularisation helps. CT and MR angiography show the narrowing, not whether it matters. ACE-inhibitor (captopril) renography is the functional test that answers that.

When to suspect it

Clinical clues

  • Hypertension beginning before 30 or after 55.
  • Controlled hypertension that abruptly worsens.
  • Resistant to three or more drugs, including a diuretic.
  • Renal function falls on an ACE inhibitor or angiotensin receptor blocker.
  • Flash pulmonary oedema, abdominal bruit, or asymmetric kidney size.

Two causes

  • Atherosclerotic — older, ostial, response to intervention unpredictable.
  • Fibromuscular dysplasia — younger, usually women; mid and distal, string-of-beads; responds well to angioplasty.

Indications and contraindications

Indicated

  • Is a known stenosis functionally significant?
  • Will revascularisation help the blood pressure?
  • Suspected fibromuscular dysplasia with intervention planned.

Not indicated

  • Screening unselected hypertensives — pre-test probability too low.

Do not perform

  • Renal function already deteriorating on an ACE inhibitor — strong evidence of critical bilateral disease or a solitary kidney. Challenging it risks further deterioration; image the anatomy instead.

Rarely worth doing

  • Solitary kidney. No contralateral control, so a post-challenge fall cannot be separated from the systemic drop in blood pressure. Usually uninterpretable.
  • Bilateral disease. Both kidneys deteriorate together and the asymmetry the test depends on disappears.
  • The test performs worst where the stakes are highest.

Caution

  • Volume depletion plus acute ACE inhibition causes symptomatic hypotension. Intravenous access, blood pressure monitoring, fluids to hand.

Why it works

How ACE-inhibitor renography works: stenosis lowers perfusion pressure, angiotensin II constricts the efferent arteriole to maintain filtration, and an ACE inhibitor removes that support so filtration falls.Renal artery stenosisPerfusion pressure at the kidney fallsRenin → angiotensin I → II (via ACE)Efferent arteriole constrictsFILTRATION MAINTAINEDACE inhibitorEfferent arteriole dilatesFILTRATION FALLSRenogram deteriorates
  • Angiotensin II constricts the efferent arteriole. Pinch the outflow and the pressure inside rises.
  • Filtration is held up despite reduced inflow — a compensation invisible on any anatomical image.
  • An ACE inhibitor removes it. Filtration falls only in the kidney that was depending on it; the normal kidney barely changes. The renogram detects the difference.
  • Same event as the creatinine rise when these patients start an ACE inhibitor.

Protocol

StepRequirement
Hydration~7 mL/kg orally 30–60 min before, or intravenous saline
ACE inhibitorsWithhold captopril 3 days; lisinopril or ramipril 5–7 days
Receptor blockersWithhold — continuing costs 15–17% of sensitivity
DiureticsWithhold 2–7 days
Captopril25–50 mg orally, tracer 60 minutes later
Enalaprilat40 µg/kg IV, max 2.5 mg, over 3–5 min; tracer 15 min later

Interpretation, and its limits

High probability (>90%) — any one, and all are a change after the challenge

  • Curve deteriorates by ≥1 grade.
  • Relative uptake falls >10%.
  • Ipsilateral GFR falls >10%.
  • Time to peak +≥2 min, or >11 min.
  • 20-minute to peak ratio rises.
  • New unilateral cortical retention.
  • Delayed excretion, prolonged transit.

Other categories

  • Low (<10%) — normal, or unchanged from baseline.
  • Intermediate — abnormal baseline, unchanged after the challenge. Cannot answer the question.

Read the right parameter

  • 99mTc-DTPA is filtered — relative uptake and GFR.
  • 99mTc-MAG3 is secreted — transit and retention; uptake stays preserved.

Limits

  • Both kidneys equally worse usually means hypotension, not bilateral disease.
  • Sensitivity 85–90%, specificity 90–95% in unilateral disease with normal renal function; both fall outside that group.
  • After ASTRAL and CORAL it is a selection tool, not a screening test.

Fuller version: Renovascular hypertension.

Take home
  • Most stenosis is incidental. Angiography finds it; renography says whether it matters.
  • High probability means change — a curve grade, 10% of uptake, 10% of GFR, a longer time to peak.
  • It measures asymmetry, so bilateral disease and a solitary kidney defeat it.
Sources
  1. Blaufox MD, De Palma D, Taylor A, et al. The SNMMI and EANM practice guideline for renal scintigraphy in adults. Eur J Nucl Med Mol Imaging. 2018;45(12):2218-28.
  2. Taylor A, Nally J, Aurell M, et al. Consensus report on ACE inhibitor renography for detecting renovascular hypertension. J Nucl Med. 1996;37(11):1876-82.
  3. Wheatley K, Ives N, Gray R, et al. Revascularization versus medical therapy for renal-artery stenosis (ASTRAL). N Engl J Med. 2009;361(20):1953-62.
  4. 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.
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