## Pathophysiology of Meniere Disease **Key Point:** Endolymphatic hydrops is the hallmark pathophysiological finding in Meniere disease, characterized by abnormal accumulation of endolymph within the membranous labyrinth. ### Mechanism of Endolymphatic Hydrops 1. **Fluid imbalance** — Disruption of endolymph production-resorption equilibrium 2. **Increased endolymphatic pressure** — Rupture of Reissner membrane (vestibular membrane) occurs during acute attacks 3. **Potassium leak** — K^+^ from endolymph floods perilymph, depolarizing vestibular and cochlear hair cells 4. **Symptom triad** — Vertigo (vestibular), hearing loss (cochlear), tinnitus (cochlear) ### Why Low-Frequency SNHL? The cochlear duct (scala media) is most affected by hydrops, and the apex (low-frequency region) is maximally distended, explaining the characteristic **low-frequency sensorineural hearing loss** that may reverse between attacks. **High-Yield:** Early Meniere disease shows **fluctuating low-frequency SNHL**; later stages show permanent high-frequency loss as hair cells degenerate. **Clinical Pearl:** Endolymphatic hydrops can be visualized on **MRI with gadolinium** (endolymphatic space enhancement) or **electrocochleography** (elevated summating potential). ### Comparison with Other Inner Ear Pathologies | Condition | Primary Defect | Hearing Loss Pattern | Vertigo Character | |-----------|---|---|---| | **Meniere disease** | Endolymphatic hydrops | Fluctuating, low-freq SNHL | Episodic, severe | | Perilymphatic fistula | Oval/round window rupture | Sudden SNHL | Positional, mild-moderate | | SSCD | Bone erosion | Conductive or mixed | Positional, sound-induced | | Acoustic neuroma | CN VIII tumor | High-freq SNHL | Progressive, asymmetric | **Mnemonic:** **HELP** = **H**ydrops, **E**ndolymphatic, **L**abyrinthine, **P**ressure.
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