Which of the following is the primary pathophysiologic mechanism in the formation of acquired cholesteatoma?

Explanation

## Pathophysiology of Acquired Cholesteatoma **Key Point:** Acquired cholesteatoma (the most common form, ~95% of cases) results from **retraction pocket formation** due to **negative middle ear pressure** and Eustachian tube dysfunction. ### Mechanism of Formation 1. **Eustachian tube dysfunction** → inadequate pressure equalization 2. **Negative middle ear pressure** develops 3. **Pars flaccida retracts inward** (most common site; pars tensa retracts in some cases) 4. **Epithelial invagination** deepens over time 5. **Keratin accumulation** → cholesteatoma mass forms 6. **Bone erosion** occurs secondarily due to pressure and enzymatic activity ### Why Pars Flaccida? The pars flaccida (Shrapnell's membrane) is the weakest part of the tympanum — it lacks the fibrous layer of the tympanic membrane and is most susceptible to retraction under negative pressure. **High-Yield:** The negative pressure is the **primary driver**; bone erosion and enzymatic activity are **secondary consequences**, not initiating factors. ### Distinction: Acquired vs. Congenital | Feature | Acquired | Congenital | |---------|----------|----------| | **Mechanism** | Retraction pocket | Embryologic rest | | **Location** | Pars flaccida (usually) | Anterior to stapes footplate | | **Frequency** | ~95% of cases | ~5% of cases | | **Associated findings** | Perforation, drainage history | Intact TM, no drainage history | **Clinical Pearl:** A history of chronic ear discharge with conductive hearing loss strongly suggests acquired cholesteatoma from retraction pocket formation.