Introduction to Hearing and Hearing Loss

Study Notes

Hearing involves sound reception by the ear, its analysis, and transmission to the brain.
Hearing impairment refers to any loss or abnormality in the structures or functions of the ear and auditory pathways.

30 dB: Equivalent to a whisper, posing no risk of hearing damage.
40 dB: Noise level typical of a refrigerator.
60 dB: Normal conversation, comfortable and safe for continuous exposure.
75 dB: Equivalent to a dishwasher, slightly louder but still within safe limits.

85-95 dB: Sounds like heavy city traffic or a school cafeteria. Prolonged exposure can cause hearing damage.
100-120 dB: Sounds from motorcycles, snowmobiles, or rock concerts. Brief exposure can be harmful.
140-165 dB: Fireworks or firearms produce these extreme sound levels. Immediate exposure can lead to permanent hearing damage.

Prelingual: loss of hearing before speech and language development.
Postlingual: loss of hearing after spontaneous speech and language development.

Conductive Hearing Loss: Originates from problems in the outer or middle ear, blocking or reducing sound transmission.
Sensorineural Hearing Loss (SNHL): Caused by damage to the inner ear or auditory nerve.
Mixed Hearing Loss: A combination of conductive and sensorineural hearing issues.

Aging: Declining hearing ability is a natural part of aging.
Loud Noise Exposure: Prolonged exposure to loud sounds can damage hair cells in the inner ear.
Infections and Illnesses: Some infections, like meningitis, can affect hearing.
Genetics: Inherited conditions can cause hearing loss.
Injury: Head trauma or injury to the ear can lead to hearing impairment.

Microtia: Deformities in the external ear ranging in severity.
External Ear Canal Atresia/Stenosis: Complete absence or narrowing of the external ear canal.
Tympanic Membrane Issues: Congenital cholesteatoma can obstruct the middle ear.
Ossicular Malformations: Malformations in the ossicular chain (malleus, incus, stapes) impede sound transmission.

Otitis Externa: Inflammation/infection of the external auditory canal or pinna.
Otitis Media with Effusion: Thick fluid buildup in the middle ear affecting eardrum mobility and sound conduction.
Cholesteatoma: A benign growth that can compress middle ear structures.
Otosclerosis: Abnormal bone growth near the stapes, restricting movement and sound transmission.
Foreign Body or Earwax Blockage: Obstructions that impede sound transmission.
Trauma: Changes in pressure, loud noises, or temporal bone fractures can lead to conductive hearing loss.

Prenatal Infections:
- Cytomegalovirus (CMV): Leading cause of sensorineural hearing loss with delayed or progressive onset.
- Toxoplasmosis: Mimics herpes, CMV, and rubella.
- Syphilis: Bacterial infection passed by pregnant mothers through the placenta.
Genetic Factors:
- Autosomal Recessive: Inherited traits leading to hearing loss with or without associated syndromes.
- Autosomal Dominant: One parent affected, the other is not.
Anatomic Abnormalities:
- Michel Aplasia (Complete Labyrinth Aplasia): Complete absence of the inner ear.
- Mondini Dysplasia: Partial malformation of the cochlea and other inner ear structures.
- Scheibe (Saccule) and Alexander (Membranous Labyrinth) Anomalies: Degeneration and malformations in inner ear components.
Environmental Prenatal Factors: Exposure to ototoxic drugs, prematurity, hypoxia, or excessive incubator noise can lead to congenital sensorineural impairment.

Infections: Bacterial meningitis.
Trauma to Temporal Bone: Injury to the temporal bone can damage structures in the inner ear.
Noise Exposure, Tumors, Radiation, Neurodegenerative Disorders: These factors can damage hair cells in the cochlea or the auditory nerve.
Renal Tubular Acidosis with Deafness: Kidney problems associated with hearing loss.
Hyperbilirubinemia: High bilirubin levels can be toxic to central auditory pathways and cochlear nuclei.