## Morphological Features of Acute Tubular Necrosis **Key Point:** ATN is characterized by loss of tubular epithelial cell integrity while the basement membrane remains intact — this is the hallmark that distinguishes ATN from more severe glomerular injury. ### Correct Morphological Features of ATN | Feature | Details | |---------|----------| | **Basement Membrane** | Preserved (intact) — critical for recovery | | **Epithelial Cells** | Flattened, loss of brush border, cellular edema | | **Mitochondria** | Swollen, dysfunctional — impaired ATP production | | **Cell Necrosis** | Focal, predominantly proximal tubule & thick ascending limb | | **Tubular Lumen** | May contain cell debris, casts, pigment | | **Interstitium** | Minimal inflammation (unlike acute interstitial nephritis) | **High-Yield:** The **preserved basement membrane** is why ATN is potentially reversible — epithelial cells can regenerate and re-epithelialize the denuded basement membrane. ### Why Glomerular Sclerosis & Crescent Formation Are NOT Features of ATN **Clinical Pearl:** Glomerular crescents and sclerosis are hallmarks of: - **Rapidly progressive glomerulonephritis (RPGN)** — crescentic GN - **Chronic glomerular disease** — focal segmental glomerulosclerosis (FSGS), membranoproliferative GN - **Lupus nephritis** — wire-loop lesions, hyaline thrombi ATN is a **tubular disease**, not a glomerular disease. The glomeruli are typically **spared** in pure ATN. **Warning:** Do not confuse ATN with: - ~~Acute glomerulonephritis~~ (glomerular injury, RBC casts, hematuria) - ~~Acute interstitial nephritis~~ (interstitial inflammation, eosinophils) - ~~FSGS~~ (podocyte collapse, proteinuria > 3.5 g/day)
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