Ear, Nose and Throat - U.S.A.  (ENT USA) Types of Hearing Loss
Types of Hearing Loss
Types of Hearing Loss - Conductive, Sensory, Neural, Sensorineural (SNHL)
  
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Signs of hearing loss can be varied.  In the child it may be the inability to normally respond to sounds and develop language.  In the adult symptoms may be tinnitus or ear ringing, fullness in the ear or difficulty understanding speech in a noisy environment. 

Search PubMed for Tinnitus Take a Self
Test On Ear Disease and Hearing Loss !!!!
   

** View Diagram of Ear **




The ear processes sounds in two important steps:     


       

     

      

  

    

  • The first is the collection and amplification of the sound, using the external ear, ear canal, eardrum and the ear bones in the middle ear.  Disease in this area of the ear will cause a "Conductive Loss" or loss of sound loudness.  Surgery will often restore the hearing to near normal levels and if the patient is unable to undergo surgery a hearing aid will greatly benefit the patient.  Even an simple auditory amplifier which costs under $50 can return the hearing to normal.  This type of hearing loss is most commonly found in children and presents as an ear infection or ear fluid.  Examples of Conductive Hearing Losses:

     

  • The second is the processing of the sound by the cochlea and converting the sound into nerve impulses and transmitting them to the brain via the auditory nerve.  The processing of the sound is very complex, parts of the sound are actually recreated by the inner ear and can be heard by use of a microphone.  This process is the basis for otoacoustic emission testing in children.  Hearing losses involving this process are called sensorineural.  Sensory for losses involving the cochlea and neural for losses involving the auditory nerve.  Sensorineural hearing losses are most common in the adult.  Unfortunately, there is no cure for these losses but the most common type, noise-induced hearing loss, are preventable.  If the loss is determined to be neuronal in type, a central lesion, such as a brain tumor, needs to be sought for.   Hearing aids will help patients with this type of hearing loss, but usually do not restore the hearing to normal.  Examples of sensorineural hearing loss:

    • Noise-induced hearing loss   Search PubMed for Noise Induced Hearing Loss

    • Presbycusis - Hearing loss associated with aging.   Search PubMed for Presbycusis

    • Meniere's Disease - Hearing loss associated with increased pressure in the endolymph (fluid contained in the cochlea).    Search PubMed for Meniere's Disease

    • Sometimes a hearing loss comes on quickly, without warning and for no know reason.  These hearing losses are called a " Sudden Sensorineural Hearing Loss ".  All other causes, such as an acoustic neuroma, should be excluded before this diagnosis is made.  There is some evidence that steroids, when given early, may help some patients.  View Article  View Article.  The use of antiviral agents are controversial with some authors having shown them to be ineffective.  View Article   Physicians have also advocated the use of agents to increase blood flow, such as plasma expanders and vasodilators but these medications have not been proven to be effective.  View Article   Conlin and Parnes (Arch Oto 2007) reviewed the randomized controlled studies for sudden hearing loss.  They concluded that there are no valid controlled study for sudden hearing loss treatment and systemic steroids should not be considered the gold standard. View Article  Treatment however should include strict limits on heavy lifting and straining.

    • Tumors of the auditory nerve - Most commonly a slowly growing benign tumor called an acoustic neuroma. 
      Search PubMed for Acoustic Neuroma
        

  •  In children a permanent hearing loss has a hereditary etiology (cause) in 39%, acquired in 30%, other causes in 7% and an unknown cause in 24%.   View Article  

 
An acoustic neuroma is a slowly growing benign tumor located on the auditory nerve.  Although benign, it can be fatal if left untreated.  Up to 10% of autopsies on normal patients have been reported to contain acoustic neuromas.  Thus, some small neuromas in older patients are followed to see if they will grow.  

Patients with a hearing loss that is worse in one ear than the other should be considered at risk for this disease.  Most should undergo a brain stem auditory evoked response or MRI scan.  

The patient shown in the right MRI scans, had only a 20 dB loss at 2000 Hz and 4000 Hz.  He had 100% discrimination (understanding of words) which is not characteristic of a neuronal hearing loss.  The neuroma showed significant growth over a 3 year period.  It was removed using a sub-occipital approach.

acoustic_neuroma_1.JPG (26973 bytes)

MRI Scan
8/30/1997
acoustic_neuroma_2.JPG (45541 bytes)

MRI Scan
8/28/2000


This patient is a 35 yr old female with a condition called neurofibromatosis.  Shown in her initial MRI scan are bilateral acoustic (ear) and orbit (eye) lesions.  She presented with a unilateral hearing loss with poor discrimination.  To learn more about neurofibromatosis, go to the National Neurofibromatosis Foundation Website:  http://neurofibromatosis.org/ 
neurofibromatosis.jpg (35567 bytes)

MRI Scan
Acoustic &
Orbital 
Lesions

    

  
 
   

   

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