Which finding on pure tone audiometry is pathognomonic for sensorineural hearing loss?

Explanation

## Sensorineural Hearing Loss: Audiometric Hallmark ### Pure Tone Audiometry in SNHL **Key Point:** In sensorineural hearing loss (SNHL), **both air conduction (AC) and bone conduction (BC) thresholds are elevated equally**, with no air–bone gap. This is the pathognomonic finding on audiometry. **High-Yield:** The absence of an AC–BC gap (AC = BC, both elevated) is the defining audiometric feature of SNHL. This occurs because the defect lies in the cochlea or retrocochlear pathway, which is bypassed by neither air nor bone conduction—both pathways converge at the inner ear. ### Pathophysiology **Mnemonic:** **SNHL = Inner ear or nerve problem** — Sensorineural Hearing Loss affects the Cochlea or auditory Nerve, so both air and bone conduction are equally affected. 1. **Air conduction pathway:** Sound → external ear → middle ear → oval window → **cochlea** ✗ (defect here) 2. **Bone conduction pathway:** Skull vibration → **cochlea** ✗ (defect here) Both pathways terminate at the cochlea; if the cochlea is damaged, both are impaired equally. ### Audiometric Patterns Compared | Type | AC Threshold | BC Threshold | AC–BC Gap | Pattern | | --- | --- | --- | --- | --- | | **Normal hearing** | ≤ 20 dB HL | ≤ 20 dB HL | None | Flat, normal | | **Conductive HL** | Elevated | Normal | > 15 dB | AC worse than BC | | **Sensorineural HL** | Elevated | Elevated | None | AC = BC, both elevated | | **Mixed HL** | Elevated | Elevated | > 15 dB | Both elevated, AC worse | ### Clinical Pearl **Absent stapedial reflex** (option D) is a sign of conductive loss (middle ear pathology), not SNHL. In SNHL, stapedial reflexes are typically **present** unless there is severe cochlear damage or retrocochlear pathology. ### Why Each Option Relates to Hearing Loss Type - **Option A (BC better than AC):** This is **conductive hearing loss**—the middle ear is broken, so AC is worse; BC bypasses it and is better. - **Option B (AC better than BC):** This is ~~not a real pattern~~ and does not occur in standard audiometry. - **Option C (AC = BC, both elevated):** This is **sensorineural hearing loss**—the inner ear is damaged, so both pathways are equally impaired. - **Option D (absent reflex, normal pressure):** This suggests **ossicular fixation** (conductive loss), not SNHL.