Deafness definition, types and causes of hearing loss

Definition: It means diminution of hearing up to complete loss, in other words: it is total or partial inability to hear sounds.
Types: There are Organic and Hysterical causes of deafness, Organic typre is classified into 3 sub-categories as discussed below.
I. Organic: A: Conductive. B: perceptive (SNHL). C: mixed.
II. Hysterical.
hearing-loss-deafness

A. Conductive hearing loss


It means interference of sound transmission along the conductive apparatus (External & middle ear).
Causes:

I. Causes in the External Auditory Canal (EAC):

II. Causes in the Tympanic membrane:

III. Causes in the Middle Ear:

IV. Causes in Eustachian tube:

  • Congenital: cleft palate.
  • Traumatic: post adenoidectomy scarring, barotrauma.
  • Inflammatory: tubal catarrh.
  • Neoplastic: nasopharyngeal tumors.
  • Miscellaneous: hypertrophy of the adenoid.

B - Sensorineural hearing loss

It means defect in conversion of sound energy to electrical impulses (cochlea) or transfer of impulses along cochlear nerve & central connections to auditory cortex.

I. Cochlear Causes (Sensory):

a. Congenital: Hearing loss dating since birth or shortly after.

1. Hereditary due to genetic aberrations:
  • If Deafness alone:

Michael’s: total lack of inner ear development.
Mondini’s: partial aplasia of labyrinth cochlea makes 1 ½ turns.
  • If Deafness with other abnormalities:
Usher’s Syndrome: SNHL + retinitis pigmentosa.
Pendred’s Syndrom: SNHL + goitre.
Alport’s Syndrome: SNHL + nephritis.

2. Prenatal:
  • Maternal infections as rubella in the 1st trimester.
  • Drug intake in the 1st trimester e.g. quinine, aminoglycosides and salicylates.
3. Natal: (during labour): 
  • Hypoxia or anoxia of the fetus.
  • Birth trauma as in forceps delivery.
4. Postnatal:
  • Neonatal infections.
  • Erythroblastosis foetalis (Rh incompatibility).

b. Traumatic

  • Transverse fracture of temporal bone involving the labyrinth.
  • Labyrinthine membrane rupture(perilymph fistula).
  • Acoustic (noise) trauma.

c. Inflammatory (Labyrinthitis)

1- Infective:
  • Viral: measles, mumps, influenza, the deafness occurs after the febrile stage. It may be unilateral or bilateral, asymmetric and affects more the high tones.
  • Syphilitic labyrinthitis: deafness is progressive, asymmetric and may be associated with vestibular symptoms (i.e. Vertigo).
  • Bacterial: - Labyrinthitis secondary to suppurative otitis media, Meningitis: deafness is bilateral and profound.
2- Toxic:
  • Ototoxic drugs: quinine, aminoglycosides, salicylates, and Lasix.
  • Metabolic: uremia, diabetes, thyrotoxicosis.

d. Vascular

Internal auditory artery occlusion due to spasm, thrombosis or embolism.
It causes sudden hearing loss (treated by large dose of steroids).

e. Miscellaneous

  • Presbycusis (senile deafness).
  • Meniere’s disease.
  • Pure cochlear otosclerosis.
  • Perilymph fistula.

II. Retrocochlear causes

Due to lesion either in the vestibulocochlear nerve, or in the auditory pathway.

1- Vestibulocochlear nerve affection:
A- Cerebellopontine angle lesions as in acoustic neuroma, and congenital cholesteatoma.
B -Meningitis.
C-Vascular loop.

2 - Central: due to lesion anywhere in the auditory pathway. It is rare.
A-Multiple sclerosis.
B-Meningitis, encephalitis.
C- Brain tumours.
D-Cerebrovascular accidents e.g. thrombosis, haemorrhage or embolism.

C - Mixed Hearing Loss

1- Congenital meatal atresia with inner ear anomaly.
2- Fracture base of skull.
3- Complicated CSOM with labryinthitis.
4- Combined otosclerosis i.e. (footplate fixation, cochlear otosclerosis).

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