A 48-year-old man is diagnosed with Meniere disease after presenting with recurrent vertigo, unilateral tinnitus, and progressive hearing loss. Which of the following is the most common site of endolymphatic hydrops in Meniere disease?

Explanation

## Anatomical Distribution of Endolymphatic Hydrops in Meniere Disease **Key Point:** The cochlear duct (scala media) is the most common and most severely affected site of endolymphatic hydrops in Meniere disease, followed by the saccule and utricle. ### Hierarchy of Involvement ```mermaid graph TD A[Endolymphatic Hydrops in Meniere]:::outcome --> B[Cochlear Duct]:::action A --> C[Saccule]:::action A --> D[Utricle]:::action A --> E[Semicircular Canals]:::action B --> B1[Most severe<br/>Low-freq SNHL]:::outcome C --> C1[Moderate involvement<br/>Vertigo, imbalance]:::outcome D --> D1[Mild involvement<br/>Subtle vestibular signs]:::outcome E --> E1[Least common<br/>Rare isolated involvement]:::outcome ``` ### Why Cochlear Duct is Most Affected 1. **Anatomical vulnerability** — The cochlear duct is a blind-ended sac with limited drainage pathways 2. **Endolymphatic sac dysfunction** — Impaired resorption of endolymph preferentially affects the cochlea 3. **Pressure transmission** — Hydrops in the cochlear duct directly compresses the organ of Corti 4. **Clinical correlation** — Hearing loss (especially low-frequency) is often the **first symptom** in Meniere disease **High-Yield:** Temporal bone histology in Meniere disease shows **maximal hydrops in the cochlear duct and saccule**, with relative sparing of the lateral semicircular canal. ### Vestibular vs. Cochlear Symptoms | Site of Hydrops | Primary Symptom | Mechanism | |---|---|---| | **Cochlear duct** | Hearing loss, tinnitus | Compression of organ of Corti; hair cell depolarization | | **Saccule** | Vertigo, imbalance | Displacement of macula; utricle involvement follows | | **Utricle** | Vertigo, postural instability | Macula utriculi compression | | **Semicircular canals** | Positional vertigo (rare) | Cupular displacement (uncommon in pure Meniere) | **Clinical Pearl:** The **cochlear symptoms often precede vestibular symptoms** in Meniere disease, and the hearing loss is **reversible early** but becomes **permanent** as hair cells degenerate with repeated hydrops episodes. **Mnemonic:** **CSU** = **C**ochlear duct (most), **S**accule (moderate), **U**tricle (mild) — order of severity in Meniere hydrops.