Causes of sensorinaural hearing loss

Sensoineural hearing loss occurs when there is damage to the inner ear (the cochlea and/or the auditory nerve). In nearly all cases there is no cure, so a sensorineural hearing loss is permanent. The damage to the ear can occur before birth, at birth or after birth depending on the cause.

Hereditary Hearing Loss

This type of hearing loss is passed onto the child through the genes from the parents. If the gene is dominant, if one or both of the parents have a hearing loss themselves they may carry a dominant gene. If the parents are normally hearing, they may carry a recessive gene. The most common type of hereditary hearing loss is from a recessive gene, which is why most deaf or hearing impaired children are born to hearing parents.
A hereditary hearing loss is usually present at birth but it may not occur until adulthood. Alternatively, a child may be born with normal hearing or just a mild hearing loss that becomes increasingly severe as the child gets older. These hearing losses may affect any of the frequencies and be mild to profound.

Hearing Loss before Birth

This may be caused by the mother taking strong medication whilst she is pregnant. There are a few drugs that when taken in large amounts, can prevent the inner ear from developing normally. There are also some infections, such as German measles or cytomegalovirus that can damage the ear if the mother gets them in the early stages of pregnancy.

Hearing Loss at Birth

There are many causes of sensorineural hearing loss at birth. If a child is born very early, at about seven months gestation, or has a very low birthweight, there may be a hearing loss. If the birth is difficult and the baby has suffered from lack of oxygen or there has been some injury to the head, there may be a hearing loss. If parents have blood of different Rhesus factor (RH- and RH+), the baby may become very jaundiced at birth. This can also cause a hearing loss.

Hearing Loss after Birth

Infection – there are many infections that can sometimes damage the cochlea, e.g. mumps, measles, and bacterial meningitis.

Injury

Severe head injuries where the skull has been fractured, may also cause damage to the inner ear.

Drugs

There are some drugs that are used to treat life threatening diseases that, if taken in large amounts, can cause a sensorineural hearing loss, e.g. streptomycin used in the treatment of tuberculosis.

Noise

Exposure to a single very loud noise (such as a nearby explosion) will immediately damage the cochlea. Also continuous exposure to loud noise over a long period of time will also damage the cochlea (such as loud music, working in a noisy factory). This cause effects the high frequencies first and will then spread to the mid and low frequencies.

Age

Almost everyone experiences some difficulty with hearing as they get older. It is gradual hearing loss that cannot be prevented and usually the high frequencies that are affected at first. There is no way to predict at what age it will occur and whether the hearing loss will be mild, moderate or severe.
It should be remembered that not all the above conditions result in a sensorineural hearing loss. For example, there are many people who get measles who have normal hearing afterwards. It is often very difficult to find out the exact cause of a sensorineural hearing loss because many people do not know exactly when the hearing problem started. This is especially true with very young children, as they do not realise that they cannot hear correctly and a hearing loss is often only identified when spoken language does not develop normally.