Causes of Unilateral Shrunken Kidney
The most important cause to identify in a unilateral shrunken kidney is renal artery stenosis (RAS), as it is potentially reversible and has significant implications for hypertension management and preservation of renal function. 1
Primary Etiologic Categories
Vascular Causes
- Renal artery stenosis is a critical diagnosis that must be excluded, as it causes progressive renal atrophy through chronic ischemia and can lead to renovascular hypertension 1
- The ACC/AHA guidelines specifically identify an atrophic kidney (7-8 cm) or size discrepancy >1.5 cm between kidneys as a Class I indication for diagnostic evaluation for RAS 1
- Fibromuscular dysplasia can cause contralateral renal artery stenosis even when the shrunken kidney appears to have parenchymal disease, making bilateral evaluation essential 2
Obstructive Uropathy
- Chronic urinary tract obstruction from urolithiasis, strictures, or congenital ureteropelvic junction obstruction leads to progressive hydronephrosis with parenchymal thinning and eventual atrophy 1, 3, 4
- Longstanding obstruction causes permanent nephron loss if not corrected, resulting in an end-stage shrunken kidney 1, 3
- Urolithiasis was documented in 69.7% of cases with unilateral hypoplastic/atrophic kidneys in one series 5
Infectious/Inflammatory Causes
- Chronic pyelonephritis with recurrent infections causes progressive scarring and renal atrophy 1
- Reflux nephropathy from vesicoureteral reflux leads to chronic damage and kidney shrinkage 1
- Pyuria was present in 66.7% of cases with unilateral small kidneys, indicating infection as both cause and complication 5
Congenital/Developmental Causes
- Renal hypoplasia or dysplasia represents developmental failure of normal kidney growth 2, 5
- These conditions may be discovered incidentally in adulthood (15.2% of cases) or present with complications 5
Traumatic Causes
- Prior renal trauma with vascular injury or parenchymal damage can result in progressive atrophy 1
Diagnostic Algorithm
When evaluating a unilateral shrunken kidney, the following systematic approach should be used:
Obtain detailed history specifically for:
Assess for clinical clues to RAS (Class I indication for further testing) 1:
- Onset of hypertension before age 30 or after age 55
- Accelerated, resistant, or malignant hypertension
- New azotemia after ACE inhibitor or ARB administration
- Kidney size discrepancy >1.5 cm
- Unexplained atrophic kidney (7-8 cm)
Perform imaging evaluation:
- CT urography provides comprehensive morphological and functional assessment to identify obstruction, stones, masses, or vascular abnormalities 1
- Renal artery imaging (CT angiography, MR angiography, or conventional angiography) when RAS is suspected based on clinical clues 1
- MAG3 renal scan to assess split renal function and determine if the atrophic kidney retains salvageable function 1
Critical Clinical Pitfalls
Do not assume the shrunken kidney is the cause of hypertension without excluding contralateral renal artery stenosis, as correction of stenosis on the normal-sized kidney may cure hypertension while nephrectomy of the small kidney would be ineffective 2
Avoid nephrectomy solely for hypertension control unless RAS has been definitively excluded and the atrophic kidney is proven to be the source through selective renal vein renin sampling or other functional studies 4
The etiology remains undetermined in approximately one-third of cases despite comprehensive evaluation, representing end-stage damage where the original insult cannot be identified 4
When pyelonephritis, reflux nephropathy, or trauma history is clearly documented, additional diagnostic testing for RAS is not indicated unless clinical features suggest a superimposed vascular process 1