Etiology and Dynamics
Nephrosclerosis is the classic terminal outcome of various glomerulopathies. The typical disease progression follows a sequence from acute glomerulonephritis to a chronic form, eventually culminating in nephrosclerosis.
The rate of progression depends directly on the primary etiology:
- Rapid progression: characteristic of focal segmental glomerulosclerosis (FSGS) and rapidly progressive glomerulonephritis (RPGN) (if the patient survives the acute episode).
- Slow progression: observed in membranous nephropathy, IgA nephropathy, and membranoproliferative glomerulonephritis.
- Asymptomatic course: sometimes preceding glomerulonephritis is subclinical and its exact type remains unidentified, with the disease presenting only at the uremic stage.
Benign Nephrosclerosis
Arteriolosclerotic (benign) nephrosclerosis develops in the setting of benign essential hypertension. Its pathogenesis is rooted in arteriolar hyalinosis, which causes focal parenchymal ischemia followed by interstitial fibrosis.
Gross appearance: Kidneys maintain normal dimensions or are moderately reduced in size (weight decreases to 110–130 g). The subcapsular surface shows a fine granularity. On cross-section, the cortex is narrowed to 0.5–0.6 cm (normal is 0.7–0.8 cm).
Microscopic findings:
- Vasculature: narrowing of the lumen of small arteries and arterioles due to wall thickening and hyalinosis. Larger vessels (interlobular and arcuate arteries) exhibit fibroplastic hyperplasia—doubling of the internal elastic lamina and smooth muscle proliferation in the tunica media.
- Parenchyma: foci of ischemic tubular atrophy alternate with zones of interstitial fibrosis.
- Glomeruli: collapse of the glomerular basement membrane, collagen deposition within Bowman's capsule, and periglomerular or total global glomerulosclerosis.
Malignant Nephrosclerosis
This form is associated with the malignant (accelerated) phase of hypertension. It is rare (affecting 1–5% of hypertensive individuals) and more frequently seen in young men. The underlying mechanism involves profoundly elevated levels of renin, angiotensin, and aldosterone. Hyperreninemia triggers generalized vasospasm, a sharp rise in blood pressure, and tissue necrosis.
Gross appearance: Kidney size is variable. A classic diagnostic hallmark is multiple petechial hemorrhages on the cortical surface, referred to as "flea-bitten kidneys". These result from the rupture of damaged arterioles or glomerular capillaries.
Microscopic findings demonstrate severe vascular damage:
- Fibrinoid necrosis of arterioles: vessel walls are infiltrated by plasma proteins and fibrin (eosinophilic granular change), often accompanied by an inflammatory infiltrate, indicative of necrotizing arteriolitis.
- Concentric arteriolosclerosis: onion-skin thickening of the intima of interlobular arteries due to concentric proliferation of smooth muscle cells and collagen.
- Necrotizing glomerulitis: glomeruli show necrosis, capillary thrombosis, and neutrophil infiltration.
Extrarenal Manifestations and Dialysis Changes
Patients with nephrosclerosis develop systemic complications secondary to uremia. Affected organ systems include the cardiovascular system (uremic pericarditis, left ventricular hypertrophy), gastrointestinal tract (uremic gastroenteritis), respiratory system (uremic pneumonitis), and bone-endocrine axis (secondary hyperparathyroidism, nephrocalcinosis, renal osteodystrophy).
In patients undergoing chronic hemodialysis, specific renal changes develop that are unrelated to the primary underlying disease:
- Intimal thickening of arteries due to accumulation of smooth muscle cells and proteoglycans.
- Calcification of glomeruli and tubular basement membranes.
- Marked crystalluria (calcium oxalate precipitation).
- Development of acquired cystic kidney disease.
- Increased risk of renal cell adenomas and adenocarcinomas.