Types of Hearing Loss
Hearing loss is classified as conductive, sensorineural, or mixed.
Hearing loss can be categorized by where or what part of the auditory system is damaged. There are three basic types of hearing loss: conductive hearing loss, sensorineural hearing loss and mixed hearing loss.
Conductive:
- malformations of the pinna and/or ear canal that are present from birth
- blockage in the ear canal such as a foreign body or cerumen (ear wax)
- perforations in the eardrum caused by trauma or disease
- middle ear infections
- broken ossicular chain (tiny bones in middle ear)
Conductive hearing loss occurs when sound is not conducted efficiently through the outer ear canal to the eardrum and the tiny bones, or ossicles, of the middle ear. Conductive hearing loss usually involves a reduction in sound level, or the ability to hear faint sounds. This type of hearing loss can often be medically or surgically corrected.
Examples of conditions that may cause a conductive hearing loss include:
- Conditions associated with middle ear pathology such as fluid in the middle ear from colds, allergies (serous otitis media), poor eustachian tube function, ear infection (otitis media), perforated eardrum, benign tumors
- Impacted earwax (cerumen)
- Infection in the ear canal (external otitis)
- Presence of a foreign body
- Absence or malformation of the outer ear, ear canal, or middle ear
Sensorineural:
Sensory
- neonatal factors
- genetic disorders
- presbycusis (hearing loss from aging)
- ototoxic drugs such as some antibiotics
- cancer treatments (chemotherapy and radiation)
- head trauma
- excessive noise exposure
- diseases of the vascular system
- kidney disease
- infections present at birth such as toxoplasmosis, rubella, CMV, herpes
- acquired infections such as the flu, meningitis, labyrinthitis, mumps
Sensorineural hearing loss not only involves a reduction in sound level, or ability to hear faint sounds, but also affects speech understanding, or ability to hear clearly.
Sensorineural hearing loss can be caused by diseases, birth injury, drugs that are toxic to the auditory system, and genetic syndromes. Sensorineural hearing loss may also occur as a result of noise exposure, viruses, head trauma, aging, and tumors.
Neural
- acoustic neuroma or other tumor of or near the nerve of hearing and balance
Mixed
- any combination a conductive, sensory, or neural hearing loss
Sometimes a conductive hearing loss occurs in combination with a sensorineural hearing loss. In other words, there may be damage in the outer or middle ear and in the inner ear (cochlea) or auditory nerve. When this occurs, the hearing loss is referred to as a mixed hearing loss.
Unilateral Hearing Loss
Unilateral hearing loss (UHL) means that hearing is normal in one ear but there is hearing loss in the other ear. The hearing loss can range from mild to very severe. Approximately one out of 1000 children is born with UHL. Unilateral hearing loss can occur in both adults and children. Nearly 3% of school-aged children have UHL.Children with UHL are at higher risk for having academic, speech/language and social/emotional difficulties than their normal hearing peers. Some children with UHL experience these difficulties but others do not.
Many times we do not know the cause of hearing loss. Below are some possible causes of UHL:
- Hearing loss that runs in the family (genetic or hereditary)
- An outer, middle or inner ear abnormality
- Specific syndromes
- Specific illnesses or infections
- Skull (temporal bone) fractures
- Excessive or extreme noise exposure
- Traumatic brain injury
The Hearing System |  |
1. The Outer Ear is made up of the pinna and the ear canal. The pinna collects sound and funnels it down the ear canal. The ear canal is curved and about 1 inch long in adults. It has hairs and glands that produce wax.
2. The Middle Ear begins with the eardrum, a membrane at the end of the ear canal. On the inner side of the eardrum is an air filled space called the middle ear cavity. The vibrations of the eardrum are transmitted through three tiny bones in the middle ear (the malleus, incus, and stapes). The stapes transmits the vibrations into the inner ear.
3. The Inner Ear has two parts: one for hearing and one for balance. The hearing part consists of the cochlea and the nerve of hearing. The cochlea is a snail shaped bony structure that contains the organ for hearing called the organ of Corti. Vibrations from the stapes activate the thousands of tiny sensory hair cell in the Organ of Corti. These hair cells then excite the nerve of hearing which carries sound to the brain.
4. The Central Auditory System is a complex network of neural pathways in the brain that is responsible for sound localization, speech understanding in noisy situations and other complex sounds such as music perception.
