## Histopathology of Cholesteatoma **Key Point:** Cholesteatoma is characterized by the presence of stratified squamous epithelium (keratinizing or non-keratinizing) with an underlying fibrous layer containing chronic inflammatory infiltrate and osteoclastic bone erosion. ### Microscopic Features | Feature | Finding | |---------|----------| | **Epithelium** | Stratified squamous (keratinizing or non-keratinizing) | | **Lamina propria** | Fibrous tissue with chronic inflammation | | **Bone erosion** | Osteoclastic resorption (hallmark) | | **Keratin debris** | Accumulation in the matrix | | **Associated structures** | Granulation tissue, cholesterol clefts | **High-Yield:** The combination of stratified squamous epithelium + chronic inflammation + bone erosion is pathognomonic and distinguishes cholesteatoma from other middle ear pathologies. **Clinical Pearl:** Bone erosion occurs due to osteoclastic activity stimulated by inflammatory mediators and pressure from the expanding keratinous mass, leading to complications like ossicular erosion and labyrinthine fistula. 
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