What is the management of a patient with a single small kidney and atherosclerotic disease of the renal artery on one side, with compensatory hypertrophy of the other kidney?

Management of Single Small Kidney with Atherosclerotic Renal Artery Disease and Contralateral Compensatory Hypertrophy

Primary nephrectomy of the atrophic kidney should be considered only when the kidney contributes <10% of total renal function (length <5 cm), revascularization attempts have definitively failed or are impossible, and the contralateral kidney appears normal with adequate compensatory function. 1

Initial Assessment of the Atrophic Kidney

Determine kidney viability before any intervention:

• A kidney length <5 cm indicates irreparable ischemic atrophy and is generally not salvageable 1
• Radionuclide scan showing <10% contribution to total renal function suggests the kidney is non-viable 1
• Evidence of extensive parenchymal damage on imaging indicates irreversibility 1
• A viable kidney is defined as >7 cm in length according to ACC/AHA criteria 1

Critical pitfall: Even a small, atrophic kidney may still contribute to blood pressure control through renin secretion, so nephrectomy should never be the first-line approach. 1

Medical Management as Primary Strategy

Optimize medical therapy first, regardless of kidney size:

• ACE inhibitors are Class I (Level A) for unilateral renal artery stenosis with normal contralateral kidney 1
• Calcium channel blockers, beta-blockers, and diuretics are all effective alternatives 1
• Exercise extreme caution with ACE inhibitors/ARBs when the contralateral kidney may have unrecognized stenosis - monitor creatinine closely 1, 2
• Aggressive cardiovascular risk factor modification including statins and antiplatelet therapy is mandatory 3, 4

The ACC/AHA guidelines emphasize that medical therapy can effectively control blood pressure and slow progression even in bilateral disease. 1

Revascularization Decision Algorithm

Consider revascularization of the atrophic kidney ONLY if:

1. The kidney is viable (>7 cm length, contributing >10% function) 1, 2
2. AND one of the following clinical scenarios exists:
   • Resistant hypertension despite optimal medical therapy (Class IIa, Level B) 1
   • Progressive renal insufficiency with bilateral disease or stenosis affecting the "good" contralateral kidney 1, 3
   • Recurrent flash pulmonary edema (Class IIb, Level C) 1
   • Acute deterioration in renal function after ACE inhibitor initiation 1, 2

Important nuance: The 2017 ESC guidelines state that routine revascularization is NOT recommended (Class III, Level A) for atherosclerotic renal artery stenosis based on recent randomized trials showing no benefit over medical therapy alone. 1, 3

Revascularization Technique Selection

If revascularization is indicated for the atrophic kidney:

• Percutaneous balloon angioplasty with stenting is first-line for atherosclerotic disease 1
• Endovascular therapy is preferred over surgery due to lower complication rates (6.3% vs 15.4%) 1
• Open surgical revascularization (aortorenal bypass with reversed saphenous vein) is reserved for:
  • Failed endovascular attempts 1, 2
  • Complex anatomy not amenable to stenting 1, 2
  • Concomitant aortic surgery already planned 1

Surgical outcomes: Primary patency rates exceed 90% for both endovascular and surgical approaches, but long-term blood pressure control and renal function preservation are similar between techniques. 1, 3

When to Perform Nephrectomy

Primary nephrectomy of the atrophic kidney is appropriate when:

• Kidney length is <5 cm with <10% functional contribution 1, 2
• The contralateral kidney demonstrates normal function and adequate compensatory hypertrophy 1
• The kidney appears hypoplastic or shows irreparable ischemic atrophy on imaging 1

Secondary nephrectomy should only be performed when:

• Revascularization attempts have failed 1
• Re-revascularization is deemed impossible 1
• Blood pressure remains uncontrolled despite maximal medical therapy 1

Critical warning: Nephrectomy leaves the patient at considerable risk if contralateral disease develops later, so renal preservation through revascularization is strongly preferred even when nephrectomy might provide adequate blood pressure control. 1

Monitoring the Contralateral Hypertrophied Kidney

Protect the functioning kidney aggressively:

• Serial monitoring of serum creatinine and eGFR every 3-6 months 2
• Annual renal artery duplex ultrasound to detect progressive stenosis in the contralateral kidney 2
• Maintain blood pressure <130/80 mmHg to prevent hyperfiltration injury 1
• Monitor for proteinuria with urine albumin-to-creatinine ratio 2

The compensatory hypertrophy indicates the contralateral kidney is bearing the entire renal workload, making its preservation absolutely critical. 1

Practical Management Pathway

For most patients with this presentation:

1. Start with aggressive medical management - multiple antihypertensive agents, statins, antiplatelet therapy 1, 3, 4
2. Assess viability of the atrophic kidney - nuclear scan and size measurement 1, 2
3. If kidney is non-viable (<5 cm, <10% function) and contralateral kidney is normal, consider primary nephrectomy 1, 2
4. If kidney is viable (>7 cm) with resistant hypertension or declining renal function, consider revascularization 1, 2
5. Reserve nephrectomy as last resort only after failed revascularization attempts 1

The evidence strongly favors renal preservation over nephrectomy whenever possible, as improved renal function after revascularization is well-documented in atherosclerotic disease with relatively sudden onset of impairment. 1, 5