Hearing Impairments

By Manjula Wanniarachchi, Clinical Audiologist, BSc (Hons) SHS, Specialized in Audiology

Hearing impairments caused by either or both structural and functional abnormalities of the auditory system. Manifestation of a lesion in the auditory system as pain in the ear or around the ear, ringing in the ear/s, blocking sensation, discharge from the ear/s, reduction in sound loudness when compare with normal, dizziness and poor speech intelligibility.

1.      Basically, hearing impairments can classified in to main two categories according to the time course

                                 Congenital and Hereditary disorders

                                 Acquired disorders

                                Congenital disorders are the disorders you are born with. Congenital disorders can affect the outer middle and/or inner ear. It can occur alone or as a part of syndromes. Abnormalities in the development of an auditory system (dysplasia) and complete lack of development an auditory structures (aplasia) are manifested as congenital disorders.

  •    Microtia (abnormally small pinna)
  •    Aural atresia (absence of an external ear canal)
  •    Aural stenosis (abnormally narrow external ear canal)   
  •    Michel’s aplasia (total absence of any inner ear structures)

 

  •  Microtia ears

                             

  • Michel’s aplasia

 

A syndrome is a pattern of abnormalities that results from the same cause. Different syndromes are associated with different kinds of hearing losses, some are appeared to be present at birth (congenital) whereas others are delayed in onset.

·         Usher syndrome-congenital

·         Hunter syndrome-progressive

Acquired disorders are the disorders you acquired after the any age of birth.

  • Head Trauma-Injuries to the head can cause any type of hearing loss.
  • Impacted Cerumen-Accumulation of wax in the ear canal
  • Foreign Bodies in the ear canal
  • Infections
  • Noise induced hearing loss-Due to exposure to high sound levels
  • Ototoxicity-Damage to the ear due to toxic effect of chemicals

 

  • Otoscopic view of an ear with impacted cerumen

  • Otoscopic view of an ear with a foreign body

  According to the location of the lesion in the auditory system, hearing impairment can categorized in to three categories.

  •  Conductive hearing loss

Due to impairments in the sound transmission pathway from the environment to the cochlea. So, it causes to reduction in signal which reach the sensorineural system than it should be. It does not affect the sensory processes within the cochlea. Disorders in the outer and middle ear. Most of conductive disorders can be treated medically and surgically.

  •  Sensorineural hearing loss

Due to lesions in the cochlea and/or auditory nerve. Disorders of the auditory nerve/eighth nerve are generally termed as retrocochlear disorders which means beyond the cochlea. Patients with sensorineural hearing loss complaint that they can hear speech but it is hard to understand. Sensorineural lesions cannot be treated medically or surgically. To overcome communication difficulties induced by sensorineural hearing loss should wear an amplification and should follow communication strategies.

  •  Mixed hearing loss

Combination of a sensorineural loss and a conductive loss in the same ear. Conductive part of the hearing loss can be treated surgically and medically whereas the sensorineural part cannot.

 

 Hearing impairments can be categorized in to six groups according to the severity of the hearing impairment.

  •  Minimal hearing loss-If any hearing threshold between 15-25 dBHL
  •  Mild hearing loss-If any hearing threshold between 26-40 dBHL
  •  Moderate hearing loss-If any hearing threshold between 41-55 dBHL
  •  Moderately severe hearing loss-If any hearing threshold between 56-70 dBHL
  •  Severe hearing loss-If any threshold between 71-90 dBHL
  •  Profound hearing loss-If any threshold between >91 dBHL

Now we have a clear idea about hearing impairment. Except congenital and hereditary hearing losses most of other hearing losses are completely preventable. Better management of hearing hygiene is most important topic in the field audiology.