How does the ear work?
It is easier to understand sensorineural hearing loss if you know more about how the ear works. The ear is made up of 3 main parts: 1) the outer ear, 2) the middle ear, and 3) the inner ear. The outer ear extends from the part of the ear you can touch to the ear drum. The outer ear acts like a funnel to direct sound to the ear drum.
The ear drum separates the outer ear and the middle ear. Behind the ear drum is the middle ear, which is normally filled with air. Three tiny bones inside the middle ear are named for their shapes: the malleus (hammer), the incus (anvil), and the stapes (stirrup). The 3 bones connect to form a chain. The first bone, the malleus, is connected to the ear drum. The last bone, the stapes, is connected to another tiny membrane called the oval window.
The oval window is the beginning of the inner ear, or cochlea. When sound hits the ear drum, the tiny bones are set in motion, and the last one pushes on the oval window, activating the cochlea. Inside the cochlea there are thousands of tiny nerve endings. These nerve endings are called hair cells and are surrounded by fluid.
The hair cells change the sound waves into electrical impulses that travel along the auditory (hearing) nerve to the brain. The brain processes these impulses and changes the sounds into something meaningful to you.
What is sensorineural hearing loss?
Sensorineural hearing loss occurs when something damages the inner ear, the auditory (hearing) nerve, or the parts of the brain that process sound. Sensorineural hearing loss includes 2 types of hearing loss: sensory hearing loss and neural hearing loss. Sensory hearing loss occurs when the cochlea or the tiny hair cells are damaged. Neural hearing loss occurs when damage occurs to the hearing nerve or the part of the brain responsible for hearing. Sometimes it is hard to tell whether the problem is sensory, neural, or both. That is why we often use the general term sensorineural hearing loss. Sensorineural hearing loss usually starts in the high frequencies (high pitches). As more damage occurs, the hearing in the lower frequencies may become worse.
What can cause sensorineural hearing loss?
Sensorineural hearing loss can have many different causes. Listed below are some of the most common causes of sensorineural hearing loss for children at St. Jude Children’s Research Hospital.
The most common types of chemotherapy that cause hearing loss are the platinum drugs or compounds. You may recognize the names of these drugs—cisplatin or carboplatin. When chemotherapy causes a hearing loss, it is usually because the drug has been absorbed into the fluid that surrounds the hair cells. This causes damage to the hair cells and keeps them from working properly. When this type of damage occurs, the hair cells cannot send signals to the brain, making it harder to hear certain sounds.
Radiation can cause sensorineural hearing loss in 2 different ways. Radiation may damage the hair cells, like chemotherapy does. Radiation may also damage the area of the brain that changes sound into meaning or the nerves that transmit electronic signals between the hair cells and the brain.
Surgery or tumors
The areas of the brain that process sound can be damaged during brain surgery. The auditory (hearing) nerve can be bruised or even cut. Swelling (edema) or a tumor pressing on the nerve can keep the nerve from working properly.
Is sensorineural hearing loss permanent?
This kind of hearing loss can be either permanent or temporary, depending on what has caused the hearing loss. The body cannot grow new hair cells. If the hair cells in the cochlea have been damaged, the hearing will not return to normal, although sometimes the hearing will get a little better after the fluid around the hair cells returns to normal. If the hearing loss has been caused by radiation, it will probably be permanent. Hearing can improve if a tumor or swelling has been putting pressure on the auditory nerve and the pressure is relieved.
However, sometimes hearing can continue to get worse long after treatment has ended. This is called a progressive hearing loss.
What happens if my child has sensorineural hearing loss?
The first step is to have a hearing test to determine the type of hearing loss and how severe it is. The audiologist and your child’s doctor will discuss possible interventions. Together, you will then be able to develop the best plan for your child.
If you have questions about sensorineural hearing loss, call Rehabilitation Services at 595-3621. If you are inside the hospital, dial 3621. If you are outside the Memphis area, call toll-free 1-866-2ST-JUDE (1-866-278-5833), extension 3621.
This document is not intended to take the place of the care and attention of your personal physician or other professional medical services. Our aim is to promote active participation in your care and treatment by providing information and education. Questions about individual health concerns or specific treatment options should be discussed with your physician.
St. Jude complies with health care-related federal civil rights laws and does not discriminate on the basis of race, color, national origin, age, disability, or sex.
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