A 52-year-old woman presents with progressive unilateral hearing loss over 18 months. Pure-tone audiometry shows the pattern marked **A** in the diagram. She reports tinnitus but denies vertigo. Speech discrimination is only 45% at 40 dB HL, despite a pure-tone threshold of 35 dB at 4 kHz. Tympanometry is normal and acoustic reflexes are present bilaterally. Which of the following is the most likely diagnosis?

Explanation

## Why Vestibular schwannoma (acoustic neuroma) is right The clinical presentation is pathognomonic for vestibular schwannoma. The pattern marked **A** — unilateral asymmetric high-frequency SNHL — is the MOST COMMON presenting feature (~95% of cases) and occurs because the slow-growing Schwann cell tumor compresses the cochlear fibers of CN VIII as it expands from the Obersteiner-Redlich zone in the internal auditory canal. Critically, the DISPROPORTIONATELY POOR speech discrimination (45% at 40 dB) relative to the pure-tone threshold (35 dB) is a hallmark of retrocochlear pathology and reflects neural compression rather than cochlear dysfunction. Normal tympanometry and present reflexes exclude conductive and middle-ear pathology. Tinnitus without vertigo is typical because slow tumor growth allows central vestibular compensation. Per Cummings Otolaryngology 7e Ch 178, unilateral asymmetric SNHL + disproportionate speech discrimination loss = MRI internal auditory canal with gadolinium to rule out vestibular schwannoma. ## Why each distractor is wrong - **Sudden sensorineural hearing loss from viral labyrinthitis**: Viral labyrinthitis presents acutely (days to weeks) with vertigo as a prominent feature and typically shows symmetric or diffuse SNHL, not the progressive unilateral high-frequency pattern marked **A**. The normal acoustic reflexes and absence of vertigo argue against acute labyrinthitis. - **Cochlear otosclerosis with stapes fixation**: Otosclerosis produces a conductive or mixed hearing loss with an air-bone gap and abnormal acoustic reflexes (absent or elevated thresholds). The normal tympanometry and present reflexes exclude this diagnosis. Additionally, otosclerosis does not produce the disproportionate speech discrimination loss seen with neural compression. - **Age-related presbycusis with symmetric high-frequency loss bilaterally**: Presbycusis is bilateral and symmetric, not unilateral. The pattern marked **A** explicitly shows unilateral asymmetric loss. Furthermore, presbycusis produces proportionate speech discrimination loss relative to pure-tone thresholds, not the marked disproportionality (45% discrimination at only 35 dB loss) that signals retrocochlear pathology. **High-Yield:** Unilateral asymmetric SNHL + disproportionately poor speech discrimination (>15% gap between expected and actual word recognition) = retrocochlear lesion until proven otherwise; order gadolinium-enhanced MRI of internal auditory canals to exclude vestibular schwannoma. [cite: Cummings Otolaryngology 7e Ch 178; Greenberg Handbook of Neurosurgery 9e]