October 29, 2012

Ask the Audiologist- Why is my doctor ordering a hearing test when I have dizziness?

Flint,-Rachel-colorBy Rachel Flint, Au.D.
Audiology Consultants, P.C.

This seems a little counterintuitive, but it is correct. There are some conditions that can affect both our balance and our hearing. The hearing test provides valuable information for identifying the cause of your dizziness. This makes more sense when we examine how the ear is structured and how it functions.

There are three main parts of the ear: the outer ear, the middle ear, and the inner ear. The outer ear is the part you see on the side of your head as well as the tunnel leading to the ear drum. The middle ear is where the eardrum is along with the three bones behind it. The inner ear is a fluid filled space embedded in the skull behind the outer ear. The part we are most interested in for the question at hand is the inner ear. The inner ear has two primary functions. One function is to transform the sound signals being received from the outer and middle ear into brain signals so that we can make sense of what we are hearing. This is done in the area known as the cochlea. Another function is to keep track of where the head is and whether or not the head is moving and is done in the area called the vestibule.

The vestibule has several different organs that are arranged perfectly between the two ears to detect movement in every possible direction. At the top of the vestibule, there are tube-like structures, known as the semicircular canals that are arranged in a circular format and at 90 degree angles from one another. These canals contain fluid. There are tiny hair cells that act as sensors at the base of each canal. As we move our head in different directions, the fluid in the tubes lags behind for a brief period of time, then it moves to catch up. You can see how this works by watching the soda in a bottle as you move the bottle back and forth. The sensors at the bottom of the canals move with the head, because they are attached to the skull. Therefore, when the fluid lags behind, it activates the sensors which then send a signal to the brain to tell it we are moving our head and in which direction. An example of the type of movement the canals detect would be turning your head to see what’s behind you.

Down below these semicircular canals, there are other organs known as the otoliths. The otoliths also have hair-cell structures that act as sensors and are arranged in different directions to account for horizontal or vertical movements of the head. There are crystals that are suspended in a gel-like fluid on top of the hair-cells. When we move in a horizontal or vertical direction, the crystals lag behind the movement, brushing the sensors, similar to how the semicircular canals work. The difference is the crystals are more sensitive to gravity since they are heavier. An example of when these organs are activated is when you put the brakes on in the car to slow down or stop.

All of these organs have identical partners in the other ear, which is how they account for all the different possible movements of the head. They work in a partnership. So, if one ear has damage, the signals being sent to the brain are not clear and do not match up with the information being received from other areas, such as the vision or the sensors in the muscles and joints of the body. This causes us to feel dizzy. The fluid mentioned above is found throughout the vestibule as well as the cochlea. There is a direct connection between the vestibule and the cochlea and it is a very small space. The entire inner ear could fit on the fingernail of your pinky finger! Therefore, it is entirely possible that something causing damage to the vestibule could also cause damage to the cochlea, or the other way around.

Diagnosing the cause of dizziness is a very complicated process. It is very important that we get as many pieces of the puzzle together as we possibly can to be sure that we get the right diagnosis. The information we gather in the hearing test is very valuable when trying to sort out what is causing your dizziness. Even if we don’t detect anything in the hearing test, the information is still valuable because we could then consider conditions that don’t involve the cochlea. So, yes, your doctor may order a hearing test if you report feeling certain types of dizziness.