Definition of Renal Atrophy
Renal atrophy is defined as a reduction in kidney size with loss of renal parenchyma, characterized by tubular atrophy, interstitial fibrosis, and decreased cortical thickness, typically manifesting when kidney length falls below 9 cm or shows loss of corticomedullary differentiation. 1
Structural Characteristics
Size criteria:
- Kidney length <7 cm indicates nonviable renal parenchyma 1
- Kidney length between 7-9 cm suggests progressive atrophy 2
- Average kidney length <14.5 cm with impaired function (serum creatinine ≥1.5 mg/dl) defines bilateral kidney atrophy in ADPKD 1
Cortical changes:
- Loss of corticomedullary differentiation with absent or minimal cortex (<0.5 cm) indicates advanced atrophy 1
- Cortical depressions overlying shrunken medullary pyramids with dilated calyces characterize segmental atrophy 3
- Tubular atrophy with colloid-filled tubular microcysts and paucity or absence of glomeruli on histology 3
Pathophysiologic Features
Microscopic findings:
- Tubular epithelial cell injury including apoptosis, proliferation, loss of differentiation, and atrophy 4
- Interstitial fibrosis with increased and activated interstitial fibroblasts 4
- Deposition of extracellular matrix proteins and loss of peritubular capillaries 4
- Interstitial inflammatory cell infiltrates composed predominantly of macrophages and T cells 4
Functional correlates:
- Renal function <10% of total renal function by scintigraphy indicates severe atrophy 2
- Proteinuria (albumin-creatinine ratio >300 mg/g or protein-creatinine ratio >500 mg/g) may arise from atrophic kidney 1
- Renal resistive index >0.8 suggests nonviable parenchyma 1
Common Etiologies
Vascular causes:
- Longstanding renal artery stenosis with chronic ischemia is a major cause 1
- Perinephric infiltration in conditions like Erdheim-Chester disease leads to progressive atrophy 1
- Atherosclerotic renovascular disease with progressive stenosis 1
Obstructive causes:
- Chronic urinary obstruction causing progressive tubular injury and interstitial fibrosis 4
- Vesicoureteric reflux, particularly when associated with infection 3
- Hydronephrosis from ureteral involvement 1
Other causes:
- Chronic kidney disease with glomerulosclerosis, tubular atrophy, and interstitial fibrosis 1
- Segmental atrophy (Ask-Upmark kidney) associated with reflux and hypertension 3
- Acquired cystic disease in chronic kidney disease 1
Clinical Significance
Prognostic implications:
- Tubular atrophy is superior to glomerular pathology as a predictor of GFR decline in CKD 5
- Renal atrophy is associated with lesion severity and progression in renal artery stenosis 1
- Left renal atrophy occurs more frequently (1.3%) than right (0.2%), possibly due to aortic pressure-induced flow disorders 6
Treatment considerations:
- Kidneys <7 cm with <10% function and renin hypersecretion (ratio >1.5) may warrant nephrectomy for refractory hypertension 1, 2
- Revascularization should be considered for high-grade stenosis with viable parenchyma (>8 cm length, cortex >0.5 cm) to prevent further atrophy 1
- Relief of obstruction does not reverse established tubulointerstitial nephritis; lesions persist and progress even after obstruction is relieved 4