What is the management approach for a patient with focal renal hypoplasia, particularly those with a history of renal issues, hypertension, or impaired renal function?

Management of Focal Renal Hypoplasia

For patients with focal renal hypoplasia causing hypertension or renal dysfunction, medical management with ACE inhibitors or ARBs should be the initial approach, with nephrectomy reserved for cases of medically refractory hypertension, persistent hypovolemia, thrombosis, failure to thrive, or when the affected kidney contributes less than 10% of total renal function. 1

Initial Assessment and Diagnosis

• Confirm the diagnosis through renal ultrasound demonstrating kidney size asymmetry, followed by radionuclide scanning to quantify differential renal function 1
• Measure renal vein renin ratios from both kidneys to determine if the hypoplastic kidney is the source of renin-mediated hypertension through activation of the renin-angiotensin-aldosterone system 2, 3
• Perform renal arteriography to distinguish between true hypoplasia and renovascular disease, as hypoplastic renal arteries appear uniformly small without segmental stenosis 4
• Assess for associated anomalies including fibromuscular dysplasia, contralateral renal abnormalities, and urinary tract malformations, as these frequently coexist with renal hypoplasia 5, 3

Medical Management Strategy

• Initiate ACE inhibitor therapy (such as enalapril) as first-line treatment, which can normalize blood pressure within 5 days in cases of renovascular hypertension from hypoplastic renal arteries 4
• Monitor blood pressure response over several weeks to months, as medical therapy can successfully control hypertension in the majority of patients 6
• Assess renal function regularly with serum creatinine and estimated GFR to detect any deterioration that might warrant surgical intervention 1
• Consider ARBs as an alternative if ACE inhibitors are not tolerated, though caution is needed with monitoring for hyperkalemia and worsening renal function in bilateral disease 1

Indications for Nephrectomy

Nephrectomy should be considered when:

• Medical therapy fails to adequately control hypertension despite optimal pharmacologic management 1
• The affected kidney contributes less than 10% of total renal function on radionuclide scanning 1
• Kidney length is less than 5 cm with evidence of extensive damage or irreparable ischemic atrophy 1
• Segmental hypoplasia is identified with elevated renal vein renin from the affected segment, in which case partial nephrectomy (resection of the hypoplastic segment) can preserve renal function while treating hypertension 2

Surgical Outcomes and Considerations

• Early nephrectomy of the hypoplastic kidney can successfully influence hypertension in 72% of cases, with moderate improvement in 16%, though 12% show no change 6
• Renal preservation should be prioritized over nephrectomy when possible, as nephrectomy leaves patients at considerable risk if contralateral disease develops later 1
• Partial nephrectomy is preferred for segmental hypoplasia to preserve overall renal function while removing the renin-producing tissue 2
• Long-term follow-up averaging 7.8 years demonstrates sustained blood pressure control in the majority of patients after removal of hypoplastic kidneys 6

Critical Pitfalls to Avoid

• Do not perform nephrectomy prematurely before attempting medical management, as ACE inhibitors can provide excellent blood pressure control without sacrificing renal mass 4
• Do not assume the hypoplastic kidney is non-functional without radionuclide scanning, as kidneys contributing more than 10% of function should generally be preserved 1
• Do not overlook fibromuscular dysplasia in young patients with hypertension and renal hypoplasia, as this may require angioplasty rather than nephrectomy 1
• Recognize that hypoplasia alone does not cause hypertension but forms the basis for its development, often requiring additional factors such as infection, ischemia, or developmental anomalies 6

Monitoring Protocol

• Refer to pediatric nephrology for children with renal hypoplasia and hypertension for specialized management 1
• Monitor blood pressure annually in all patients with congenital renal anomalies 7
• Obtain yearly serum creatinine to assess for progressive renal dysfunction 1, 7
• Consider nephrology referral for adults with GFR less than 30 mL/min/1.73 m², though stable isolated findings may only require specialist advice rather than formal ongoing care 1