A 45-year-old man presents 36 hours after waking with complete deafness in his left ear, roaring tinnitus, and ear fullness. Otoscopy is normal bilaterally. Weber test lateralizes to the right (normal) ear; Rinne shows air-bone conduction is normal bilaterally. Pure-tone audiometry reveals the pattern marked **B** in the diagram — severe sensorineural hearing loss of 75 dB averaged across 0.5, 1, 2, and 4 kHz on the left, with normal hearing on the right. Speech discrimination on the left is 20%. No preceding URI, ototoxic exposure, head trauma, or vertigo. Which of the following is the MOST CRITICAL next diagnostic step to exclude a life-threatening structural lesion?

Question

Accepted Answer

B. MRI with gadolinium of the internal auditory canal to rule out vestibular schwannoma. ## Why MRI with gadolinium of the internal auditory canal is right

The audiogram pattern marked **B** — severe unilateral SNHL of sudden onset with normal otoscopy and normal bone conduction — is consistent with idiopathic sudden sensorineural hearing loss (ISSNHL). However, vestibular schwannoma (acoustic neuroma) accounts for 1–3% of unilateral SNHL cases and presents identically: sudden unilateral hearing loss, tinnitus, and normal otoscopy. MRI with gadolinium is the gold standard to exclude this structural lesion, which requires surgical or radiosurgical intervention. Per AAO-HNS guidelines, MRI of the internal auditory canal is mandatory in all cases of unilateral SNHL to exclude retrocochlear pathology before initiating corticosteroid therapy. This is the most critical diagnostic step because missing a schwannoma delays definitive treatment and worsens prognosis.

## Why each distractor is wrong

- **High-resolution CT temporal bone**: CT is useful for conductive loss (ossicular chain, stapes fixation) and temporal bone fracture, not for retrocochlear lesions. The Rinne test is normal bilaterally, ruling out conductive pathology. CT does not detect intracranial masses.
- **Electrocochleography**: While ECoG can suggest endolymphatic hydrops (Ménière disease), it does not exclude structural lesions and is not part of the standard ISSNHL workup. Ménière typically presents with episodic vertigo, which this patient lacks.
- **Caloric testing and video head impulse test**: These assess vestibular function and are appropriate if vertigo is present. This patient has no vertigo, and vestibular testing does not exclude a schwannoma; imaging does.

**High-Yield:** Unilateral SNHL is a vestibular schwannoma until proven otherwise — MRI with gadolinium is mandatory before starting steroids.

[cite: AAO-HNS Sudden SNHL guideline]

Answer

A. Electrocochleography to confirm endolymphatic hydrops

Answer

C. High-resolution CT temporal bone to assess ossicular chain integrity

Answer

D. Caloric testing and video head impulse test to assess vestibular function

Explanation

Why MRI with gadolinium of the internal auditory canal is right

Why each distractor is wrong

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