What is the appropriate workup for an incidentally discovered severely atrophic right kidney?

Workup for Incidentally Found Severely Atrophic Right Kidney

An incidentally discovered severely atrophic kidney (<9 cm or >1.5 cm size discrepancy) requires immediate diagnostic evaluation for renal artery stenosis (RAS), as this represents a Class I indication and potentially reversible cause of both kidney atrophy and hypertension. 1, 2

Initial Clinical Assessment

Key Historical Features to Obtain

• Blood pressure history and current control status - specifically assess for resistant hypertension (failure to achieve goal BP on 3 drugs including a diuretic), accelerated hypertension, or malignant hypertension with end-organ damage 1, 2
• Prior episodes of unexplained pulmonary edema, particularly if azotemia is present 1, 2
• Response to ACE inhibitors or ARBs - new azotemia or worsening renal function after initiation is itself a Class I indication for RAS evaluation 1, 2
• History of pyelonephritis, reflux nephropathy, or trauma - these should be excluded as alternative causes of atrophy before attributing it to RAS 2, 3
• Age at hypertension onset - onset before age 30 or severe hypertension after age 55 raises suspicion for RAS 1

Essential Laboratory Evaluation

• Serum creatinine and estimated GFR to establish baseline renal function 2
• Urinalysis and urine albumin-to-creatinine ratio to assess for proteinuria and active sediment 2
• Consider split renal function testing with renal scintigraphy (MAG3 or DTPA) to determine if the atrophic kidney contributes >10% or <10% of total renal function, as this threshold guides management decisions 2, 4

Diagnostic Imaging Strategy

First-Line Anatomic Imaging for RAS

Renal artery imaging is the cornerstone of evaluation for atrophic kidney with suspected RAS 2:

• CT angiography (CTA) - non-invasive first-line option for anatomic assessment of renal arteries 2
• MR angiography (MRA) - alternative non-invasive option, particularly useful in patients with renal impairment where contrast exposure should be minimized 2
• Renal duplex ultrasonography - radiation-free option but operator-dependent 2
• Conventional angiography - gold standard when intervention is planned 2

Functional Assessment

• Renal scintigraphy with MAG3 or DTPA provides split renal function assessment and helps determine the functional contribution of the atrophic kidney 2, 4
• Segmental/selective venous renin sampling should be considered if nephrectomy is being contemplated - a renin ratio >1.5 (atrophic kidney to contralateral kidney) identifies patients most likely to respond to nephrectomy 2, 4

Management Algorithm Based on Findings

If RAS is Identified with >10% Split Function

• Optimize medical management first with multiple antihypertensive agents including diuretics 2
• Consider endovascular revascularization for patients with atrophic kidney function >10% of total renal function and significant stenosis (>70%) 4
• Studies demonstrate revascularization can reduce systolic BP by 26 mmHg and diastolic BP by 14 mmHg without significant impairment of renal function 4

If Atrophic Kidney Has <10% Function

• Medical management is preferred when split function is <10% and renin ratio <1.5, as nephrectomy is unlikely to improve BP control 2
• Nephrectomy may be considered for patients with <10% split function AND renin ratio >1.5, particularly with refractory hypertension 2, 4
• Be aware that nephrectomy can reduce systolic BP by 40 mmHg and diastolic BP by 19 mmHg, but may cause greater reduction in GFR than predicted by preoperative scintigraphy 4

If No RAS is Found

• Investigate alternative causes including chronic obstruction, prior infection, congenital anomalies, or vascular abnormalities 3
• Continue medical management of hypertension if present 2

Critical Pitfalls to Avoid

• Do not use ACE inhibitors or ARBs without extreme caution if bilateral RAS or stenosis to a solitary functioning kidney is suspected, as new azotemia after initiation is a Class I indication for RAS evaluation 1, 2
• Do not perform nephrectomy solely for hypertension control without documenting both <10% split function AND renin ratio >1.5, as the functional threshold may need to be lowered to 5% to limit postoperative GFR reduction 4, 3
• Do not assume the atrophy is benign - the severity of renal function impairment is associated with reduced survival (3-year survival of only 51% for creatinine ≥2.0 mg/dL) 1