A 52-year-old man with a 3-week history of sudden unilateral hearing loss and tinnitus is evaluated. Otoscopy is unremarkable. Weber test shows lateralization to the affected ear. Rinne test shows air conduction better than bone conduction on the affected side. Which investigation is most appropriate to rule out retrocochlear pathology in this patient?

## Investigation of Choice: ABR with MRI Brain ### Clinical Context The patient presents with classic features of **sudden sensorineural hearing loss (SSNHL)**: - Acute onset (3 weeks) unilateral hearing loss - Tinnitus (cochlear symptom) - Normal otoscopy (rules out conductive cause) - Weber lateralizing to affected ear (confirms sensorineural loss) - Rinne showing air > bone conduction (confirms sensorineural pattern) ### Red Flag: Asymmetric Sudden SNHL **Key Point:** Sudden unilateral SNHL is a **medical emergency** and may indicate retrocochlear pathology (e.g., acoustic neuroma, vestibular schwannoma, central lesion). Unlike gradual bilateral SNHL, acute asymmetric loss *requires* imaging to exclude structural lesions. **High-Yield:** Approximately 5–10% of sudden SNHL cases have an identifiable retrocochlear or central cause. ABR is the most sensitive non-imaging test for 8th nerve dysfunction; MRI is the gold standard for structural diagnosis. ### Why ABR + MRI? 1. **ABR (Auditory Brainstem Response):** - Assesses integrity of the auditory pathway from cochlea → 8th nerve → brainstem - Detects retrocochlear pathology (8th nerve lesions, brainstem dysfunction) - Abnormal findings (prolonged latencies, absent waves) suggest 8th nerve compression or demyelination - Highly sensitive for acoustic neuroma (>95% sensitivity for tumors >1 cm) 2. **MRI Brain (with contrast, internal auditory canal protocol):** - Gold standard for visualizing 8th nerve and cerebellopontine angle - Detects acoustic neuroma, meningioma, or other mass lesions - Rules out central causes (brainstem stroke, demyelination) **Clinical Pearl:** The combination of ABR + MRI has >99% sensitivity for detecting acoustic neuroma. If ABR is normal and MRI is negative, retrocochlear pathology is excluded, and the diagnosis is idiopathic SSNHL (managed medically with corticosteroids). ### Comparison of Investigations in Sudden SNHL | Investigation | Role in Sudden SNHL | Sensitivity for Retrocochlear Pathology | |---|---|---| | **ABR + MRI** | **GOLD STANDARD** — detects 8th nerve & structural lesions | >99% for acoustic neuroma | | **Pure Tone Audiometry alone** | Confirms SNHL & severity; does NOT rule out retrocochlear cause | 0% — audiometric findings cannot exclude neuroma | | **Tympanometry** | Rules out middle ear pathology | 0% — irrelevant for SNHL | | **OAE** | May be abnormal in cochlear loss but normal in 8th nerve lesions | Low — cannot differentiate cochlear from retrocochlear | **Warning:** A common mistake is ordering pure tone audiometry alone and assuming normal results exclude retrocochlear pathology. Acoustic neuromas can present with *cochlear* hearing loss patterns (normal air-bone gap) because the tumor compresses the cochlear nerve, not the middle ear. ### Algorithm: Sudden SNHL Workup ```mermaid flowchart TD A[Sudden unilateral hearing loss]:::urgent --> B[Otoscopy + Weber + Rinne]:::action B --> C{Sensorineural pattern?}:::decision C -->|No| D[Conductive loss — tympanometry]:::action C -->|Yes| E[SSNHL confirmed]:::outcome E --> F[ABR + MRI brain]:::action F --> G{Retrocochlear pathology?}:::decision G -->|Yes| H[Neurosurgery referral]:::urgent G -->|No| I[Idiopathic SSNHL]:::outcome I --> J[Corticosteroids ± other therapy]:::action ``` **Mnemonic:** **SUDDEN SNHL = ABR + MRI** — **S**udden **U**nilateral **D**eafness **D**emands **E**xclusion of **N**euroma — **A**BR + **M**RI **R**equired **I**mmediately.