‫بسم هللا الرحمن الرحيم‬
‫‪HEARING LOSS.‬‬
Definition of hearing loss.
• Detectable impairment of hearing.
• The term deafness is limited to cases with
profound or total hearing loss.
Classification of hearing loss.
• Types:
• Severity:
1- Conductive H.L.
2- Sensory H.L.
3-Neural H.L.
4- Sensori-neural H.L.
5- Central H.L.
6- Mixed H.L.
7- Psychogenic H.L.
1- Mild:
20-40dB
2- Moderate: 40-60 dB
3- Severe:
60-90 dB
4- Profound: 90-110 dB
5- Total:
>110 dB
A- Conductive hearing loss.
• External auditory canal:
1- Atresia.
- Congenital.
- Acquired.
2 – Complete obstruction:
- Impacted wax.
- Foreign body.
- Debris or discharge.
- Tumour.
A- Conductive hearing loss.
*Tympanic membrane:
1- Perforation.
2- Retraction/adhesions.
3- Tympanosclerosis.
*Ossicular chain:
1- Discontinuity:
- Head trauma.
- Inflammatory.
2- Fixation:
- Otosclerosis.
- Tympanosclerosis.
- Congenital.
A- Conductive hearing loss.
• Middle ear fluid:
- Serous: S.O.M.
- Pus: Acute Supp. O.M.
- Blood: Haemotympanum.
• Windows obstruction:
- Otosclerosis.
* Eustachian tube dysfun.
How drum or ossicular
abnormalities affect hearing?
• 99.9% of sound energy is lost when the
sound pass from air to a fluid medium.
• Pressure transformer system of the middle
ear:
1- Hydraulic ratio action (areal ratio) = 17
2- Ossicular lever action = 1.3
Pressure transformer system.
• Hydraulic ratio action (areal ratio):
- Ratio between the surface area of the ear drum
(90mm) & that of the foot plate of stapes (3mm).
- Vibrating area of the T.M= 55mm.
- Areal ratio= 55/3 = 17 i.e. increase in the sound
energy falling on the foot plate by 17 times.
Pressure transformer system.
• Ossicular lever action:
• Ratio between the length of the handle of
malleus to the long process of incus = 1.3
• Sound P transformer mechanism of the middle
ear = areal ratio x ossicul. Lever action= 22
(this increases the sound energy by 26dB).
B- Sensori-neural H.L.
• Hearing loss due to a lesion affecting
the cochlea(sensory) or the auditory
nerve (neural).
• Causes:
- Congenital: consanguinity or perinatal.
- Traumatic: barotrauma, noise trauma,
temporal bone
fracture.
- Inflam.: bacterial, viral or specific ($).
- Neoplastic: CPA tumour, glomus.
B- Sensori-neural H.L.
-
Aging : presbyacusis.
Ototoxic drugs : aminoglycosides.
Autoimmune diseases.
Meniere’s disease.
Metabolic or endocrinal dis.: DM.
CNS lesions: DS.
Idiopathic sudden H.L.
Diagnosis of H.L.
• Depends on 3:
1-History.
2- Examination.
3- Hearing tests.
• To answer 3:
1- Where is the lesion?
2- What is the lesion?
3- Severity?
Hearing tests.
1- Tuning fork tests.
2- Pure tone audiometry.
3- Speech audiometry.
4- Tympanometry&acoustic reflexes.
5- Auditory evoked potentials.
A-Tuning fork tests.
1- Weber test.
Tuning fork tests.
2-Rinne test.
B- Pure tone audiometry.
• This is a qualitative and quantitative method.
• Idea: delivering sounds of variable frequencies and
intensities to the ear via an earphones and a bone
vibrator and recording the patient’s response on a chart.
• Determine the threshold of hearing at the start of the
procedure (the minimum intensity of sound necessary to be
audible in at least 50% of presentations).
B- Pure tone audiometry.
Normal < 20dB.
Severe 60-90dB.
Mild 20-40dB.
Profound 90-110dB.
Moderate 40-60dB.
C- Speech audiometry.
• Records the patient’s response to words, it
includes:
1- Speech discrimination score (SDS).
2- Speech reception score (SRS).
Scores are excellent in cochlear lesions and
poor in retrocochlear lesions.
D- Tympanometry&acoustic
reflexes.
• Tympanometer is important to:
1- Test the mobility of the ear drum and the ossicular chain
(compliance):
- reduced mobility: e.g. tympano-ossicular fixation.
- Absent mobility: e.g. middle ear effusion.
2- measurement of acoustic reflex (stapedius cont.):
- absent reflex: e.g CHL.
- Impaired reflex: e.g. SNHL.
Normal.
e.g. SOM.
e.g. Eustacian tube
dysfunction.
E- Auditory evoked potentials.
• Idea: recording the electrical current along the
auditory pathway.
1- Cochlea: electrocochleography.
2- Nerve&brain stem: auditory brain stem response.
3- Subcortical centers: middle latency response.
4- Auditory cortex: cortical auditory potentials.
Treatment.
• CHL: Medical or surgical treatment according
to the cause.
• SNHL:
1- Medical: Intratympanic or general.
2- Hearing aids.
3- Surgical: e.g. Cochlear implant.
END.