A 38-year-old woman presents with sudden-onset hearing loss in the right ear for 3 days, associated with vertigo and tinnitus. She denies ear discharge or trauma. On examination, the right tympanic membrane is intact and normal. Weber test lateralizes to the left ear. Rinne test shows air conduction better than bone conduction on the right side. Audiometry reveals a moderate-to-severe sensorineural hearing loss at all frequencies on the right, with normal hearing on the left. What is the primary pathophysiological mechanism underlying this hearing loss?

Explanation

## Sudden Sensorineural Hearing Loss (SSHL) Pathophysiology ### Clinical Diagnosis **Key Point:** SSHL is defined as ≥30 dB hearing loss at three consecutive frequencies occurring over ≤3 days. This patient meets all criteria: acute onset (3 days), unilateral, sensorineural pattern. ### Pathophysiological Mechanisms in SSHL 1. **Viral Labyrinthitis** (most common theory) - Direct viral invasion of cochlear epithelium - Inflammation and edema of cochlear structures - Damage to hair cells and supporting cells 2. **Vascular Insufficiency** - Thrombosis or vasospasm of labyrinthine artery - Ischemia of cochlear tissue - Hair cell necrosis due to hypoxia 3. **Autoimmune Mechanism** - Immune-mediated attack on cochlear antigens - Complement activation and inflammation ### Audiometric and Clinical Findings | Finding | Interpretation | | --- | --- | | Air > Bone conduction | Confirms sensorineural pathology (normal cochlear function would show bone ≈ air) | | Unilateral loss | Excludes presbycusis, noise-induced loss (bilateral) | | All-frequency involvement | Suggests cochlear-wide pathology (viral, vascular, or autoimmune) | | Vertigo + tinnitus | Indicates inner ear involvement beyond cochlea (vestibular system) | | Normal tympanum | Rules out conductive causes | **Mnemonic: SSHL Causes — VIVA** - **V**iral (labyrinthitis) - **I**schemic (vascular) - **V**accine-related (autoimmune) - **A**utoimmune ### Why This Is Sensorineural, Not Conductive ```mermaid flowchart TD A[Acute Hearing Loss]:::outcome --> B{Tympanum Normal?}:::decision B -->|Yes| C{Air > Bone?}:::decision B -->|No| D[Conductive Cause]:::outcome C -->|Yes| E[Sensorineural Loss]:::outcome C -->|No| F[Mixed Loss]:::outcome E --> G{Unilateral?}:::decision G -->|Yes| H[SSHL - Viral/Vascular]:::action G -->|No| I[Bilateral - Systemic]:::action ``` **High-Yield:** In SSHL, the site of lesion is the cochlea or retrocochlear nerve, NOT the middle ear. Hair cell death is the final common pathway regardless of etiology. **Clinical Pearl:** Vertigo accompanying sudden hearing loss suggests labyrinthitis (viral) rather than pure cochlear ischemia, as the vestibular system is also affected.