Hearing Loss

The Problem

If you are experiencing hearing loss, the problem is usually obvious to you. People must speak louder, you may need to turn the volume up on your headphones, or you may not be able to hear speech or music at all. But to your physician, your problem is far from straightforward. There are many types and even more causes of hearing loss, and it is your doctor's job to first identify the particular form of hearing loss, its cause, and finally the available treatment option. For example, your doctor may determine that you have conductive hearing loss, and then order a temporal bone CT scan to determine why. The scan may demonstrate that you have longstanding ear inflammation and your physician may then recommend a surgical procedure. This is just one of many possible scenarios; the list is nearly endless.

What causes hearing loss?

Hearing involves a complicated pathway that carries sound waves through the parts of your ear that you can see, into air-filled cavities within your skull, through dense bone, tiny nerves and finally, your brain. Problems with any of these areas can result in difficulty hearing. For example, the cause may be as simple as too much wax built up in your ear, or it may be related to an injury in your ear drum. These areas can generally be easily seen and no further work-up may be necessary. Your history may provide clues, as well. For example, if you've had trouble hearing since birth, your doctor may suspect a congenital cause for your hearing loss - in other words, something you were born with. If your hearing loss started abruptly and is accompanied by an earache, your doctor may suspect acute otitis media, or, more simply, an ear infection. Be prepared for lots of questions! Your doctor will want to know how long you've had trouble hearing, whether it was sudden or gradual, and if there are other symptoms, like pain, fluid leaking from your ear (otorrhea), dizziness or unusual sounds. This information will help your doctor narrow down the very long list, and will help determine what kind of further testing is necessary.

What are the basic types of hearing loss?

  1. Conductive hearing loss: The sound waves are unable to reach the nerves within your inner ear. This may occur because of a mechanical blockage to sound transmission, such as wax or fluid in your ear, or a problem with the small bones in your middle ear.
  2. Sensorineural hearing loss: The neural pathways involved in hearing cannot function properly. There is a problem with the nerves or portions of the brain involved in hearing.
  3. Mixed hearing loss: There is a combination of conductive and sensorineural hearing loss.

A short list of possible diagnoses...

The following represent some of the more common diagnoses in hearing loss. This list of names you might hear is only a small fraction of possible diagnoses:

  1. Congenital (diseases you are born with): external auditory canal atresia, vestibulocochlear dysplasia, large vestibular aqueduct syndrome
  2. Acute (diseases with rapid onset): serous otitis media, acute otitis media, acute otitis externa, tympanic membrane perforation
  3. Chronic (diseases with gradual onset that are present for months or more): cholesteatoma, otosclerosis, labyrinthitis ossificans, acoustic neuroma, presbycusis

What kinds of tests will my doctor order?

  • Once again, there are lots of possibilities, but after examining you and learning your history, your doctor will be able to decide on a customized way to proceed. Some of the tests may occur in your doctor's office, and will most likely include an examination with a tuning fork as well as a more formal audiogram, where you will listen to tones and speech through a headset. In some cases, your doctor may order a radiological test to evaluate areas that can't be seen on physical examination. The most common radiological examinations ordered for hearing loss are CT (computed tomography or CAT scan) and MRI (magnetic resonance imaging). CT scans are just specialized forms of X-rays that can give very detailed information about the appearance of the bones involved in hearing. If your doctor has determined that your hearing loss is conductive (involves a problem with the sound waves moving through the air cavities or bones), a CT scan is usually the place to start. If, however, your doctor has found that your hearing loss is sensorineural (there is a problem with the nerves and portions of the brain involved in hearing), an MRI may be the starting point.

What are CT and MRI scans like?

    The scanners look similar, and require you to lie on a stretcher that will move into what looks like a large donut. The MRI scanner has a thicker "donut" and uses magnetic fields to look at the deeper structures involved in hearing. In many cases, your doctor will order the MRI with contrast. This means that you will get an injection of a fluid called gadolinium into a vein, generally in your arm. This contrast agent has been used for years, is very safe and has few side effects. The technologist or nurse will generally ask you to fill out a questionnaire to determine whether the scan and contrast injection can be performed safely, as well as a consent for the contrast injection. CT scans are less commonly ordered with contrast, but if your doctor requests it, the procedure will be similar. The contrast agent for CT is different: it is a substance that contains iodine, which shows up on the X-Ray images that the CT scanner generates. Both CT and MRI examinations are painless, though some people with claustrophobia find MRI examinations difficult. The technologist will ask you about claustrophobia, as well.

What about the results?

When the scan is completed, it will be processed and sent to a radiologist for interpretation. The radiologist will review the information that your doctor has provided about you, analyze the images, and generate a written report which will be sent to your doctor, often with a copy of the images on a CD. Sometimes the radiologist will speak with your doctor, to get more information about you or to convey the results directly. You will get the results of the scan through your doctor's office. At this point, a number of things may occur. If the results of all the information that the doctor has accumulated, including the CT or MRI scans, point to a diagnosis, it will be time to discuss treatment options. If the cause of your hearing loss is still unclear, it is possible that the doctor may order further testing; for example, if the CT scan was normal, or negative, an MRI may be ordered, depending, again, on all the information your doctor has accumulated to this point. Some of the most common causes of hearing loss have no findings on physical or radiology examinations: these include presbycusis (hearing loss with age) and prolonged exposure to loud noise (all those concerts when you were young!) In either case, your doctor will have ruled out many of the other important causes of hearing loss, and a hearing aid will likely do the trick.