Brain Injury and Hearing Loss

Brain Injury

Brain Injury can be broadly classified as

  • Traumatic brain injury: Traumatic brain injury is injury to the brain, not of degenerative or congenital nature, resulted due to an external physical impact/force which may produce a declined or different level/state of consciousness, which results in an reduction of cognitive/mental abilities or physical functioning. It can also result in the disturbance of emotional or behavioural functioning. This kind of brain injury is related to accidents.

  • Acquired brain injury: Acquired brain injury is Injury to the brain (which is not hereditary, congenital or degenerative) that has occurred after birth but not due to any injury. Common examples include loss of oxygen to the brain, infection in the brain and stroke.

Brain injuries which were either present at the time of birth or are progressive (acquired over time) in nature (Parkinson's or Alzheimers disease are not classified under acquired or traumatic brain injury.

The Ear, Hearing and Brain Injury

Temporal Bone (Lobe), mastoid Process
Fig 1: Temporal Bone (Mastoid Process)
Hearing problems after a brain injury can happen either due to mechanical problems (passing to sound to brain) or neurological problems (brain's ability to process the sound). Neurological problems are more likely to happen when the temporal lobes (within temporal bone) and/or inner ear have been damaged. After behavioural testing, all patients should get there hearing screened and ears examined (Otoscopic examination). Head injury can result in any of the following damage to the ear's part which may result in hearing loss or auditory dysfunction:

  • Middle ear damage
  • Injury to Cochlea in ear
  • External bleeding in the ear canal
  • Temporal lobe lesions (abnormality in the tissue of an organism)
  • Eardrum or ossicular chain damage
  • Disruptions of intralabyrinthine fluid
  • Cochlea damage
  • 8th cranial nerve damage.

After a head injury, a person can have loss/reduction in hearing even if there is no direct/visible damage to the ear. This can be caused due to reduction in brains ability to process the sound. A neck injury can also result in tinnitus (ringing of ear).

Brain injury hearing loss can be further classified according to the location of injury

ossicular chain and Eardrum
Fig 2: Ossicular chain and Eardrum

Conductive hearing loss

Damage to ear drum or ossicular chain: Conductive hearing loss happens when there is difficulty passing sound waves through ear. This type of hearing loss can be caused due to disruption to the ossicular chain (three small bones in the middle ear space) or ear drum. When the ear drum is ruptured/perforated but ossicles remain attached the hearing is reduced. When the ossicular chain is disrupted, it can cause complete hearing loss. Blood or fluid within the middle ear can also reduce hearing.

Ruptured Eardrum
Fig 3: Ruptured Eardrum

Most patients with tympanic membrane perforations have pure conductive hearing loss. This is also true for hemotympanum (presence of blood in the tympanic cavity of the middle ear). Patients with closed post-traumatic conductive hearing loss, have roughly equal fractions of mixed and conductive hearing loss.

Perilymph fistula is an tear or defect in a thin membrane, which separates middle ear (which is filled with air) and inner ear (which is filled with fluid). Under Perilymph fistula, the sufferer feels dizziness and imbalance which is triggered by blowing or straining the nose. Loud noise can also cause dizziness for people suffering with fistula (also known as Tullio's phenomenon).

Post-traumatic Meniere's syndrome (also know as endolymphatic hydrops or just hydrops) cause incidents of dizziness followed by noises in the ear, feeling of fullness, or changes in hearing. This it probably caused by the bleeding inside inner ear, due to disturbance in fluid transport.

Ear Labyrinth
Fig 4: Ear Labyrinth

Cochlear hearing loss

Airbag injuries: Sudden deployment of air-bags after car accident cause a significant incidence of vertigo (sensation of everything around you is spinning or moving) and disturbance in hearing.

blast injuries:The hearing loss due to blast are associated with excessive noise (please see article on Noise Exposure and Hearing Loss).

Labyrinthine "concussion": Defined as a intermittent disturbance in hearing or labyrinthine which happens after a head injury and not associated with any other cause..



Auditory Vestibular Nerve, Vestibulocochlear Nerve, 8th Cranial Nerve
Fig 5: 8th Cranial (Vestibulocochlear) nerve

Neural hearing loss

The 8th Cranial nerve (Vestibulocochlear nerve) is hard to access as it is encased in hard bone. Neural hearing loss is due to damage to the 8th nerve, such as due to temporal bone fracture, or traction on the nerve between the lip of the IAC and brain.



Prevention

Treatment is individualised to the diagnosis. Treatment usually includes a combination of hearing assistive devices, medication, and counselling about prognosis. Occasionally, surgery may be recommended.