Skip to content

Hearing

Sensorineural hearing loss

Damage to the hair cells of the cochlea or the auditory nerve. Sounds become both quieter and less clear — and this is the loss that surgery cannot repair, only compensate.

  1. Sound
  2. Eardrum
  3. Ossicles
  4. Cochlea
  5. Auditory nerve
  6. Auditory pathways
  7. Brain
  8. Communication

What it is

Sensorineural hearing loss (SNHL) arises in the inner ear or the auditory nerve. On the audiogram, air and bone conduction are reduced together: there is no gap, because the problem lies beyond the point where bone conduction enters the system.

The usual culprits are the hair cells — the outer hair cells that amplify soft sounds and sharpen frequency tuning, and the inner hair cells that send the signal to the nerve. Hair cells do not regenerate. Their loss has two effects: sounds need to be louder to be heard, and, more troublesome, the signal that reaches the brain is smeared, so that even sounds that are loud enough are harder to understand.

Causes

Age (presbycusis) and noise are by far the commonest, followed by genetic causes, some medications (aminoglycosides, cisplatin, high-dose loop diuretics), viral and immune inner-ear disease, Ménière’s disease, head injury, and, rarely, a tumour on the nerve (vestibular schwannoma). Otosclerosis can also involve the cochlea, converting a conductive loss into a mixed one.

Sudden sensorineural hearing loss — hearing that drops over hours or up to three days, usually in one ear — is a medical urgency. Treatment with steroids is more effective early. Anyone who wakes with one ear muffled and no obvious blockage should be seen within days, not weeks.

Why clarity suffers

With outer hair cell loss, the cochlea’s fine frequency tuning broadens. Neighbouring sounds blur into each other. Consonants — the short, high-frequency, low-intensity parts of speech that distinguish fit from sit from hit — are the first casualties. Add background noise and the blurred signal becomes ambiguous; the brain fills in gaps, at a cost in effort. This is why “I can hear but I can’t understand” is the signature complaint of sensorineural loss, and why amplification alone does not fully solve it.

Beyond hair cells

Loss of synapses between inner hair cells and auditory nerve fibres (cochlear synaptopathy), particularly of low-spontaneous-rate fibres, has been proposed as a mechanism for speech-in-noise difficulty with a normal audiogram; its clinical significance in humans remains debated. Retrocochlear causes should be considered in asymmetric SNHL, disproportionately poor word recognition, or abnormal reflex decay, with MRI of the internal auditory canals the investigation of choice. Auditory neuropathy spectrum disorder presents with absent or abnormal ABR and present otoacoustic emissions, and responds unpredictably to amplification.

What can be done

No operation repairs a damaged cochlea. Treatment is compensation, and the options are good:

  • Hearing aids, fitted and verified properly, with directional microphones and noise management.
  • Cochlear implants when aids no longer give useful speech understanding, now including single-sided and asymmetric losses.
  • Communication strategies, assistive listening in difficult places, and realistic expectations.
  • Protection of what remains: noise, ototoxic drugs where alternatives exist, and prompt treatment of sudden loss. Earplugs work: in a randomised trial at a live music festival, temporary threshold shift occurred in 8% of protected ears against 42% of unprotected ears (research).

Relevance to ear surgery

Sensorineural loss sets the ceiling for any middle-ear operation. Closing an air-bone gap in a mixed loss brings hearing up to the bone-conduction line and no further. And the inner ear’s fragility is exactly why hearing preservation is a fixed part of every surgical decision on this site.

This page provides general educational information. It cannot replace an individual assessment, which depends on a full history, examination, audiometry and, where relevant, imaging. If you have sudden hearing loss, severe pain, facial weakness, severe dizziness or discharge with fever, seek medical care promptly.