Hearing Overview

 

 

Hearing is one of those special senses that many of us take for granted. Oftentimes, it is only when we lose this special gift, that we realize its importance. In the early days, there was not very much to be done about hearing loss. People cupped their ears and made other people shout louder to hear. Before the industrial revolution, crude devices shaped like trumpets were developed to collect and funnel sound into the ear. That represented the birth of the hearing aid. As technology progressed, it was discovered that there were different types of hearing loss that could be treated in a variety of ways. Some forms of hearing loss were easy to treat, while others were not so easy. Simple wax removal could miraculously restore hearing in certain individuals while others remained deaf despite all treatments. 

 

 

How Hearing Works

In order to understand the various treatment options, it is important to understand some of the anatomy and physiology of the ear.

The ear is divided into three main parts, the outer ear, the middle ear, and the inner ear. The outer ear consists of the auricle and ear canal and eardrum. Essentially, it is the job of the outer ear to channel sound to the eardrum. The ear acts as a funnel. The auricle, like the cone shaped portion of the funnel, collects sound and passes it through the ear canal and directs sound to the eardrum. 

The middle ear is an air containing space that houses the three hearing bones, the hammer/malleus, anvil/incus and the stirrups/stapes. Vibration of the ear drum sets off vibration of the hearing bones. These three hearing bones are connected in such a way that using mechanical leverage, they are able to amplify sounds and transmit the vibrations to the inner ear. The inner ear is completely encased in bone and consists of a cochlea and a labyrinth. The cochlea is a snail shaped structure that is attached to the labyrinth. It is responsible for hearing. Inside the cochlea, the vibrations transmitted by the hearing bones move little hair cells. High-pitched sounds stimulate high-pitched hair cells that are located at the base of the spiral. These specialized hair cells, in turn, fire off nerve impulses that the brain interprets as high-pitched sounds. Low tone sounds stimulate low tone hair cells that are located at the apex of the spiral. 

 

 

What Can Go Wrong?

 

Hearing loss is generally divided into two distinct types -- conductive loss and nerve loss (also called sensorineural hearing loss or SNHL). 

Conductive hearing loss occurs when sound cannot be "conducted" to the inner ear. In other words, something is causing the sound vibrations to be dampened. Simple obstruction of the ear canal with wax can cause conductive hearing loss. An ear canal that is too narrow can be another cause of conductive hearing loss. Problems that cause conductive hearing loss usually reside at the external ear or middle ear. The following is a list of some causes of conductive hearing loss: 

 

	Otitis Media: Fluid in the middle ear can dampen sound vibrations.
	Tympanic membrane perforation: A large hole in the ear drum, like a hole in a pocket, allows some sound energy to escape and be wasted.
	Hearing bone problems:

	Otosclerosis: Stiffening of the stirrups bone, like arthritis restricts transmission of sound. Trauma -- dislocation of the hearing bones can disrupt transmission of sound. Scar formation -- can happen after many recurrent infections.
	Middle ear tumors: Cholesteatoma, granuloma, glomus tumors etc. can dampen vibrations. Nerve loss occurs when there is a problem with the inner ear or hearing nerve. The problem usually happens at the level of the hair cells. For instance, if hair cells at the base of the spiral cochlea grow weak and die, a high frequency nerve hearing loss will occur. Hair cell damage can occur in many ways. The following are some causes for sensorineural hearing loss. Presbycusis -- a fancy name for age-related hearing loss. Noise induced hearing loss: loud noises enter the cochlea near the base of the spiral and damage these cells first. The point of contact usually occurs at 4000 Hertz.
	Meniere's disease: Excessive inner ear hydraulic pressures can cause hearing to fluctuate.

	Congenital: Genetics can cause some parts of the inner ear to not form correctly.
	Acoustic neuroma: This and other brain tumors can cause pressure on the hearing nerve and thus disrupt transmission of sound.
	Sudden onset sensorineural hearing loss: This is a type of nerve hearing loss that occurs rapidly over the course of hours to days because of damage to the inner ear hair cells. If the cells are injured but not dead, there is a chance of recovery. Sudden onset sensorineural hearing loss is a medical emergency that should be treated (typically with steroids) as soon as possible.

Treatments

	Wax removal
	Hearing aids
	Tympanostomy and tubes

	Tympanoplasty (Repair of Eardrum)
	Stapedectomy
	Cochlear Implantation

	BAHA implant
	Envoy Esteem implant

 

The wonderful thing about conductive hearing loss is that it is usually reversible. Removal of obstructions can allow sound to enter the ear better. Drainage of fluid in otitis media can allow the hearing bones to vibrate more freely. 

 

On the other hand, sensorineural hearing loss is usually irreversible -- with only a few exceptions. (The main exception for the irreversibility of nerve loss is that of "sudden onset sensorineural hearing loss" (SSNHL) when it is properly treated with steroids.) Typically, nerve loss is slowly progressive. It usually occurs with advancing age and chronic long-term noise exposure.  

 

The treatment for nerve hearing loss patients is amplification. In these modern times, this is done electronically with the use of hearing aids. Hearing aids consist of tiny microphones and speakers that boosts the volume of incoming sounds. There are many types and configurations of hearing aids, each of which has its own advantages and disadvantages. "Behind the ear" hearing aids are the most powerful, however they are also cosmetically more noticeable. Digital hearing aids can give clearer sounds, however they are usually more expensive. Wearing hearing aids is much like wearing glasses. Patients usually don't know what they're missing until they've tried them. Choosing the proper hearing aid is much like choosing a stereo system. Although there may be a world of difference electronically between a simple a.m. transistor radio (for five dollars) and a high fidelity Dolby system (that costs thousands of dollars); the user must choose what is comfortable for his or her personal taste. The complexity of features and circuitry within the hearing instruments determines the cost of the device.