CHILDHOOD HEARING LOSS
Hearing is a vital sense. Detecting sound is essential for children to acquire language, socialize, develop their intellectual capabilities, for safety, and to enjoy the world around us. Hearing loss is the most common form of sensory impairment. In the United States each year, 4000 children are born deaf and 37,000 more are born with milder degrees of hearing loss. Other children will develop hearing loss in a delayed time frame from acquired diseases, trauma, or from genetic reasons.
A conductive impairment may result from a blockage of the external canal such as earwax or more severe from a congenital defect where the ear canal is extremely narrow (stenosis) or does not form at all (atresia). Often the external ear or auricle will be misshapen (microtia) or rarely even absent (anotia).
More common causes of childhood conductive hearing loss are from chronic ear infections and middle ear fluid and congestion. Eardrum perforation (hole) or damage to the ear bones (ossicles) can result. Children with chronic ear infections usually have poorly functioning eustachian tubes leading to poor aeration of the middle ear. Chronic ear infections require medical (antibiotics) or surgical treatment such as ear tubes, removal of infection from the middle ear or mastoid and eardrum or ear bone repair (tympanoplasty, mastiodectomy, ossicular reconstruction).
Lastly, trauma may cause eardrum or ear bone damage. Encourage children never to put foreign objects into the ear canal.
The causes of childhood sensorineural hearing loss are many and complex. Pediatric hearing
loss can be organized into four main categories:
A. Inherited Sensorineural Hearing Loss
B. Non Hereditary Sensorineural Hearing Loss
C. Inherited Sensorineural Hearing Loss With
D. Non Hereditary Sensorineural Hearing Loss
With Associated Syndromes
A syndrome is a set of independent features that occur together that have a common cause. There
are more than 200 syndromes that include deafness or hearing loss.
An individual’s physical traits are a combination of the genetic material received from their parents. Diseases can also be passed on to offspring on a genetic basis. Hereditary sensorineural hearing loss is estimated to occur in more than 27 per 1000 persons. Inherited profound hearing loss occurs in 1 per 1000 births. The mode of inheritance is usually recessive (77%), but can
be dominant (22%), or more rarely sex linked, mitochondrial inheritance, or even from spontaneous mutations. Studying the family history and a genetic consult can help determine the chances of future offspring being affected with hearing loss. There is great variability of the types of inherited hearing loss. The child can have mild to profound loss, congenital or delayed, stable or progressive, low frequency loss, mid frequency loss or high frequency loss.
Many causes of childhood hearing loss are not inherited but instead are acquired. The most severe losses usually occur from some insult or disease affecting the developing fetus. This is referred to as acquired prenatal hearing loss. Examples of this type of hearing loss would be congenital infections like rubella (measles), syphilis, or cytomegalovirus (CMV). Other causes could be lack of oxygen to the baby at birth or high levels of a pigment (bilirubin) after birth. Severe infections after birth such as meningitis or repeated middle ear and mastoid infections can damage a child’s hearing.
In many cases inherited hearing loss will occur with other defects or abnormalities. These are called syndromes and often named by the individual who first describe them. The hearing loss can be associated with skin, facial, skeletal, eye, neural, or metabolic abnormalities. Some of the more common syndromes with hearing loss are Waardenburg’s syndrome (wide set eyes, broad nasal root, white forelock, different colored iris, and congenital deafness) Usher’s syndrome (progressive vision loss due to retina deterioration and deafness), Treacher-Collins syndrome (jaw and mid-face deformity and hearing loss, and Alport’s syndrome (progressive kidney deterioration and hearing loss). Some syndromes are dominant inheritance, other recessive, and other spontaneous.
Many syndromes associated with hearing loss are not inherited. For example, Fetal Alcohol syndrome is caused by excessive alcohol by the mother during pregnancy and is characterized by an unusual facial appearance and sometimes hearing loss. A more common disorder associated with ear and hearing loss is Down’s syndrome. Though it is a genetic abnormality of chromosome 21, it is not inherited. It is important to identify syndromes to better know the characteristics and prognosis of the condition. Many syndromes are discovered by the appearance of the child, laboratory tests, xrays of the ear, or by consultation with other specialists like an opthamologist or genetic expert.
Some children’s hearing loss result from a “central” or brain processing problem. In these individuals the ear structures (eardrum, ear bones, and some parts of the inner ear) are functioning normally. The problem resides in other parts of the inner ear, the hearing nerve or the brain itself. This type of loss can be very difficult to diagnose and require special testing. The child will have troubles understand speech in noise and localizing sound. Treatment consists of reducing background noise and designing an individualized educational program. Also hearing aids or a cochlear implant may be of help.
It is not always possible to determine the cause of childhood hearing loss. Your doctor will seek many clues to make the best diagnosis possible. Information regarding the mother’s pregnancy, the child’s birth and further development, and family history will be obtained. A complete physical exam, laboratory tests, x rays, and hearing tests are also vital.
The earlier a hearing loss can be discovered the more effective is the treatment. A delay in diagnosis slows a child’s development of speech and language. This is so critical that many states have passed laws requiring all newborns to have their hearing screened. Special testing (auditory brainstem test and otoacoustic emissions) can discover hearing loss in even a newborn child.
The treatment of childhood hearing loss varies with the cause and severity of loss. Infections affecting the ear and hearing can be treated medically with antibiotics or antiviral medicines. Conductive hearing loss can frequently be repaired with surgery. Surgery ranges from the simple (ear tubes) to the complex (ear canal reconstruction / atresia repair – see next section).
Sensorineural hearing loss is primarily treated with hearing aids. Profound and severe sensorineural hearing loss are helped by the cochlear implant. All types of hearing loss benefit from intensive educational efforts and preferential classroom seating.
Microtia refers to a malformed outer ear. Atresia refers to an absent ear canal. Ear deformities can occur as an inherited disorder or from some damaging event or substance (teratogen) during the development of the fetus. One or both ears may be involved. The majority of times no cause can ever be found.
Surgery can be performed to correct congenital malformed ears. It often requires the skills of a plastic/reconstructive surgeon and an ear surgeon and several surgical steps. The external reconstruction is done to improve the appearance of the outer ear. The ear canal reconstruction goal is to improve hearing to a serviceable hearing. In the case of an unilateral hearing loss, repairing the atresia allows the child to hear with both ears. Surgery is delayed until the child is approximately age 5 or later.
If the parents chose to do external ear reconstruction, then the microtia surgery is done first. The plastic surgeon will perform three to four separate procedures at least 3 months apart. Typically, rib cartilage is used as a framework for the new ear.
The ear canal/atresia repair usually requires only one surgery. However to determine if a successful surgery is possible, preoperative hearing tests will be done to determine the ear’s potential. A detailed xray (CT scan) is also done before surgery. In certain cases, the temporal bone will be so malformed that surgery is not safe or there is a poor chance of restoring hearing. If this occurs, then the child can rely on a bone conducting hearing aid such as the BAHA device.
Atresia surgery is done under general anesthesia and last 3 to 4 hours. A new ear canal is drilled open into the middle ear. The ear bones are often deformed and immobile. They may require mobilization or replacement. The new ear canal is lined with a skin graft taken from the arm or leg. After the repair, the ear will be protected with packing for 1 to 2 weeks.
Risks involved in atresia surgery are further hearing loss, reclosure of the new ear canal, or rare injury to the facial nerve. Fortunately in experience hands complications are unusual and the surgery is successful.