The hearing impairment is one of the most frequent sensory deficient in human population. Consequences of hearing impairment include inability to interpret speech sounds, often producing a reduced ability to communicate, delay in language acquisition, economic and educational disadvantage, social isolation and stigmatization. The function of the ear and the hearing process play an important role in the verbal communication between individuals and make a noticeable impact on individual’s life. So, we decide here to talk about hearing function of the ear from many different points of view. These points of view will include mainly the anatomical, physiological and pathological basis of ear and hearing process. After that, we will talk about the common types and causes of hearing loss and the possible applicable methods to treat these conditions.

1. Republic of Iraq
Ministry of higher education &
scientific research
University of Baghdad
College of medicine
Student selected component (SSC)
Conductive & sensorineural
hearing loss
Human Structure and Function (HSF)
module
Abbas A. A. Shawka
‫شوكة‬ ‫عباس‬ ‫احمد‬ ‫عباس‬
2nd
stage
2018 A.D. 1439 A.H.

2. 2 |
Contents
1. Introduction ..……………………………………………………................................. 3
2. Anatomy of the ear …………………………………………………………………... 3
2.1 External ear ……………..……………………………………................... 4
2.2 Middle ear ………………………………………………………………... 4
2.3 Inner ear………………………………………………………. …………. 6
2.4 Auditory pathway ………………………………………………………... 9
3. Physiology of hearing …………………………………………………...................... 10
3.1 Conduction of sound waves …………………………………………….. 10
3.2 Transduction of sound waves ……………………………........................ 12
3.3 Neural transmission of signals ………………………………………….. 14
3.4 Neural process of auditory information ………………………………… 14
4. Hearing loss …………………………………………………………………………. 15
4.1 Types of hearing loss ……………………………………………………. 15
4.1.1 Conductive hearing loss ………………………................ 15
4.1.2 Sensorineural hearing loss SNHL ………………………. 16
4.1.2.1 Presbyacusis …………………………….. 17
4.1.2.2 Meniere’s disease ……………………….. 17
4.1.2.3 Noise-induced hearing loss ……………... 17
4.1.3 Mixed hearing loss ……………………………................ 17
4.2 Genetic causes of hearing loss ………………………………………….. 18
4.3 Clinical approaching to a patient with hearing loss …..…………............ 18
4.4 Treatment of hearing loss ……………………………………………….. 20
4.5 Prevention ……………………………………………………………… 22
5. Epidemiology …………………………………………………………...................... 23
6. Summary ……………………………………………………………………………. 24
7. References …………………………………………………………………………... 25

3. 3 |
1. Introduction
The hearing impairment is one of the most frequent sensory deficient in human
population.(1)
It affects more than 360 million people.(2)
Consequences of hearing impairment
include inability to interpret speech sounds, often producing a reduced ability to communicate,
delay in language acquisition, economic and educational disadvantage, social isolation and
stigmatization.
The function of the ear and the hearing process play an important role in the verbal
communication between individuals and make a noticeable impact on individual’s life. So, we
decide here to talk about hearing function of the ear from many different points of view. These
points of view will include mainly the anatomical, physiological and pathological basis of ear
and hearing process.
After that, we will talk about the common types and causes of hearing loss and the possible
applicable methods to treat these conditions.
2. Anatomy of the ear
You can imagine the ear as a tube make a connection between the surrounding environment
and the hearing centers in our brain.
The ear is composed of three parts, external, middle and inner ear. These three parts of the
ear are located within the temporal bone. See figure (1)
Figure (1): Pathway of sound reception.(3) With some editing made by the author.

4. 4 |
2.1. The external ear
It is composed of two parts, one attached to head laterally (auricle) and a canal ( external
acoustic meatus ) that pass inward and somewhat forward to terminating at a thin membrane
called the (tympanic membrane). The auricle is part of the ear that project laterally from the
head and assist in capturing the sound.
External acoustic meatus is 2.5cm in length and extends from the concha (central part
of the auricle ) to the tympanic membrane. The external acoustic meatus is not straight.(4)
It
takes an s-shaped course, from the external opening, this meatus pass anteriorly and upward
then still pass upward but posteriorly then it will pass anteriorly but in descend. This is why
physician pulls the auricle upward and posteriorly in the otoscopic examination. If you want to
straight the meatus in infant, you have to pull the auricle inferioposteriorly (down and back ).(5)
Its outer third is cartilage, its inner two-thirds bone; in both zones the skin is firmly adherent.(6)
The outer third which supported by cartilages contains, in the submucosa layer hair
follicles, sebaceous gland and modified apocrine sweat gland called “ ceruminous glands. The
sebaceous and ceruminous glands secrete a waxy material called the (cerumen) that has a
protective anti-microbial properties.(7)
The tympanic membrane separates the tympanic cavity from the external acoustic
meatus, it lies obliquely making 55° with the floor of external acoustic meatus in adults. Its
longest, anteroinferior diameter is 9–10 mm, and its shortest is 8–9 mm.(8)
The tympanic
membrane is thickened by a fibrocartiliginous ring called “ annulus “, this annulus conatins
radially oriented smooth muscle that have an important role in controlling blood flow and
tension of the membrane.(9)
The lateral surface is concave, The inner surface of the membrane
is thus convex and the point of greatest convexity is termed the umbo.(8)
The attachment of the
handle of malleus is superior to the umboo in an anterior direction, at the most superior line of
this attachment there is a small bulge marks the position of the lateral process of malleus.
Extending away from this elevation, on the internal surface of the membrane, are the
anterior and posterior malleolar folds. Superior to these folds the tympanic membrane is thin
and slack (the pars flaccida), wherease the rest of the membrane is thick and taut (the pars
tensa).(4)
2.2. Middle ear
Middle ear is an air-filled space in the temporal bone with mucous-membrane lining. It
located between inner ear medially and the tympanic cavity laterally. This space has a
communication with the mastoid area posteriorly and the nasopharynx anteriorly. This room-
like structure has six walls, each wall with a specific features and structures related to it, and
all these features and structures can be observed in figure (2).

5. 5 |
Figure (2) Boundaries of the right middle ear.(4)
Important notes that are necessary to be considered in middle ear anatomy is a
fallowing. Middle ear has a close relation to vital structures like internal carotid artery, internal
jugular vein and fascial nerve, so, a lesion in one of these structures can affect the middle ear
and vice versa. The auditory ossicles (malleus, incus, stapedius) are found inside the middle
ear, along with an associated muscles, tensor tympani that attached to the malleus, and
stapedius that attached to stapes, there is different source of innervation for these two muscles.
Malleus is attached to tympanic membrane and articulated with incus, incus articulates with
both malleus and stapes, stapes had a footplate that when moved it can attached the oval
window of the inner ear. There is a synovial joints between the auditory ossicles.(6)
Generally, these ossicles are responsible for converting the sound waves from the air
filled cavities to the fluid-filled cavity. A special consideration on how these ossicles and
associated muscle work will be discussed in the physiology of hearing.
The mastoid air cells mucous membrane is in continuous with that of middle ear, and
that is the cause why mastoiditis is usually secondary to middle ear infection.(4)
Pharyngotympanic tube (Eustachian tube) connects the anterior wall of middle ear with
the nasopharynx. This tube is not straight in adults, it is directed forward, downward and
medially. In children, Eustachian tube is shorter, smaller and straighten so that they are more
prone to infection.(10)

6. 6 |
Figure (3): Comparison
between Eustachian tube in
children and adults.(3)
2.3. Inner ear
Inner ear is located between the middle ear laterally and the internal acoustic meatus
medially.
Figure (4): location of inner ear components.(11)
Simply, inner ear composed a bony cavities with a membranous cavities and sacs
within it. These called the (bony labyrinth) and (membranous labyrinth). Labyrinth means
tortuous anatomical structure
Bony labyrinth, which is filled with a fluid called “perilymph”, is composed of :
1- Vestibule
2- Three semicircular canals
3- Cochlea
Figure (5): Right bony labyrinth (otic capsule),
anterolateral view: surrounding cancellous bone
removed.(3)

7. 7 |
Membranous labyrinth, as shown in figure (6), is composed of
1- semicircular ducts.
2- cochlear ducts.
3- two sacs, utricle and saccule.
Figure (6): (Right membranous labyrinth with nerves) medial view. (3)
The function of the inner ear is related to both hearing and equilibrium. cochlea is the
organ of hearing while semicircular ducts within the semicircular canals, utricle and saccule
within the vestibule composed the organ of balance as shown in figure (6).
It is important to notice that, cochlear duct is indirectly continuous the the saccule,
while the semicircular ducts are directly continuous with the utricle.
Important notes to be considered in inner ear anatomy that related to hearing process
are mainly about the cochlea and as follow. You can imagine the cochlea as a core of bone,
when another bone twist around it, it will form this structure called cochlea
That is the cochlea is composed of a core of bony structure called the modulus with a
spiral bone around it. The base of cochlea faces the internal acoustic meatus when it is
perforated by the cochlear nerve.(8)
Figure (6) shows a section through a turn of cochlea. We notice this, a thin lamina
called (osseous spiral lamina) will project from the modulus side of the canal, and partially
divided this canal. Basilar membrane then will completely divide this canal. Another two
membranes, Reissner”s membrane orginate from this lamina and end in the opposing wall of
the canal, tectorial membrane, also arises from the lamina but it is attached to hair cells in
(organ of corti) that rest on the basilar membrane. Organ of corti is responsible for hearing.

8. 8 |
Figure (7): A section through a turn of cochlea.(3)
Then this bony canal will divided into three compartments, scala vestibule, scala
media (it is the same as the choclear ducts) and scala tympani.
Scala vestibule and scala tympani are filled with perilymph, which is resemble the
composition of extracellular fluids, while scala media ( cochlear duct ) is filled with endolymph
which is resemble the composition of intracellular fluids.
Scala vestibule and scala tympani are connected to each other at th helicotrema ( the
end of last turn of choclea ). Scal vestibule is in continuous with the vestibule, while scala
tympani is separated from the cavity of the middle ear by secondary tympanic membrane that
covers the round window.
Perilymph fills all regions of the bony labyrinth and has an ionic composition similar
to that of cerebrospinal fluid and the extracellular fluid of other tissues, but it contains little
protein. Perilymph emerges from the microvasculature of the periosteum and drains via a
perilymphatic duct into the adjoining subarachnoid space. Perilymph suspends and supports
the closed membranous labyrinth, protecting it from the hard wall of the bony labyrinth. See
figure (8).
Figure (8): a cross section through the petrous bone showing the drainage of both
endolymph and perilymph.(12)

9. 9 |
Endolymph fills the membranous labyrinth and is characterized by a high-K+ and
low-Na+ (16 mM content, similar to that of intracellular fluid. Endolymph is produced in a
specialized area in the wall of the cochlear duct called ( stria vascularis ) that is rich in blood
vessels, and drains via a small endolymphatic duct into venous sinuses of the dura mater. See
figure (9).
Figure (9): histologic section of choclear duct, with arrow point to stria
vascularis, a specialized epithelial cells in the lateral wall of cochlear duct that
are in contact with blood vessels in periosteum.(7)
No physiological contact exist between endolymph and perilymph, and when one of
them have a leakage, this will be consider as a pathological condition.
2.4. Auditory pathway
1- Spiral ganglion ( located in the modulus
bone )
2- Superior olivary nucleus complex,
trapezoid nucleus and nucleus of lateral
lemniscus.
3- Inferior colliculus,
4- Medial geniculate body and
5- Auditory cortex. See figure (10)
Figure (10): auditory pathway.(13)

10. 10 |
Vestibulocochlear nerve (VIII) is a cranial nerve that responsible for transmitting signals
of hearing and balance to higher brain centers, it nuclei are located in pons. Specific nuclei for
the cochlear component of this nerve are dorsal and ventral cochlear nuclei. Some fibers from
these nuclei ascend to become the lateral meniscus on the same side, other fibers ( the majority)
will decussate and form the trapezoid body then ascend to become the lateral meniscus on the
contralateral side. So, a cut in the auditory pathway, above the trapezoid body on one side, will
affect both ears but it is more prominent on the other side.
3. Physiology of hearing
Sound wave is a type of mechanical waves that need a media (e.g. air or fluid) to convey
through. It is conducted in medium as a compressions and rarefactions. Special characteristic
of sound wave is shown in figure (11).
Figure (11): characteristics of sound wave. (Note: this picture could be find in
any Website or Textbook concerned with physics of sound)
Physiology of hearing can be discussed under these heading:
1. Conduction of sound waves
2. Transduction of sound waves
3. Neural transmission of signals
4. Neural process of auditory information
3.1. Conduction of sound waves
a. Role of external ear:

11. 11 |
Pinna is important for collecting and reflecting sound to external auditory meatus, it also
help to determine whether the sound came from the front or back
external auditory meatus, as previous mentioned, is s-shaped, and this help in amplifying
the sound wave, protecting tympanic membrane from injury and to heat and humidate air, as it
pass through it.
b. Role of middle ear
Tympanic membrane vibration will cause the ossicles to vibrate, so, the tympanic
membrane act as pressure receiver, resonator and to dampen the sound wave (e.g. vibration of
tympanic membrane is immediately after the end of sound). (14)
Mechanism of conduction from middle to inner ear involves the following:-
1- Impedance matching mechanism:
The air- filled middle ear is serving to conduct the sound to the fluid-filled inner ear, and
since water is has a much more impedance to sound waves than air, so, mechanism to amplify
the sound must be exist.
Mechanisms to amplify sound include the following:-
a. Lever action of ossicles: whereas the handle of malleus is 1.3 longer than the long
process of incus, this provides a leverage advantage to which the ossicles increase
the force of movement by 1.3 times.
b. Hydraulic action of the tympanic membrane: the effective vibratory area of the
tympanic membrane (about 45 square millimeter) is much greater than the stapes
oval window surface area (about 3.2 square millimeter). This size difference means
the force produced by sound waves is concentrated over a very small area, the oval
window, and this will amplify the pressure exerted on oval window by 14 folds.
c. Curves membrane effect: the tympanic membrane is more moveable at the
periphery than the center, whereas the handle of malleus is attached, this will
provide some leverage.
So, these three mechanism increase the sound pressure 18 folds
(i.e. 14 x 1.3).
When the tympanic membrane and the ossicles are removed, and the sound waves strike
the oval window directly, even very loud sounds are heard as whispers.(15)
2- Phase difference between oval and round window
If sound waves is applied to oval and round window at the same time, they will cancel each
other’s effect, with no perilymph movement and no hearing. This phase difference is provided
by intact middle ear and fluid-filled area around the round window.

12. 12 |
3- Natural resonance of external and middle ear
Specific ranges of frequencies are more easily to pass through external and middle ear to
inner ear, this is due to the inherent anatomical and physiological characteristics of both the
external and middle ear.
The greatest sensitivity of the sound transmission is between 500 and 3000 Hz, and these
are the frequencies most important to human in day-to-day conversation.(15)
4- Attenuation reflex
When there is a loud sound, a specific reflex will be initiated that will cause to
contraction of both muscles in middle ear. Tensor tympani muscle contraction will cause the
tympanic membrane to be more tense, then harder to be vibrate by the louder sound, and this
is a protective mechanism against loud sound. Stapedius muscle contraction cause the footplate
of stapes to get away from the oval window, so, protecting the cochlea from damage by loud
sound. Also, this reflex will minimize the sensitivity to Parsons’s own voice.
3.2. Transduction of sound waves
Transduction of sound wave involve the converting of the mechanical sound wave into
electrical signals, and this happens in organ of corti. This will involve the vibration of basilar
membrane, stimulation of the hair cells and membrane potential changes in hair cells.
a. Vibration of basilar membrane
When the footplate of stapes strike the oval window, this will make the sound wave to
pass to the inner ear. This sound wave will spread along scala vestibule.
Most of the sound energy is transferred directly from the scala vestibuli to the scala
tympani. Very little of the sound wave ever reaches the helicotrema at the apex of cochlea.(15)
So, basilar membrane will vibrate in response to sound energy that pass from scala
vestibule to scala tympani
It is important to note that the part of the cochlea where height of pressure wave reaches
its maximum varies with the frequency of sound. See figure (12).

13. 13 |
Figure (12): Traveling waves” along the basilar membrane for high-, medium-,
and low-frequency sounds. “ Stretched basilar membrane “.(16)
b. Stimulation of hear cells
Because of the tectorial and basilar membrane attached at different points to the limbus
(the other side of the cochlear canal), they will slide on each other as they vibrate up and down.
We have two types of hair cells in organ of corti, outer hair cells which are few, and
inner hair cells which are the predominant. It is belived that inner hair cells are responsible for
the membrane potential changes that occurs after stimulation, while the outer hair cells will be
responsible for influencing the action of inner hair cells, since this cells has a descend (efferent)
innervation from the central nervous system (CNS).(17)
When the organ of Corti moves up, the tectorial membrane slides forward relative to
the basilar membrane bending the stereocilia away from the limbus.
When the organ of Corti moves down, the tectorial membrane slides backwards relative
to basilar membrane and bends the stereocilia towards the limbus
This bending in sterocilia will excite the hair cells, and when this bending is away from
the limbus, hair cells will be depolarized, and if the bending was toward the limbus, a state of
hyperpolarization will be observed in the hair cells. See figure (13)

14. 14 |
Figure (13): movement of organ of corti and sterocilia of hair cells.(15) With
some editing made by the author.
c. Membrane potential change in hair cells
This is, as previously mentioned, due to the bending and displacement of hair cells. It
is important to know that, even in resting conditions, there is electrical activity in the inner ear.
3.3. Neural transmission of signals
This was previously discussed in the auditory pathway, but here we will talk about
specific characteristics that are unique for this pathway:-
1. Bilateral representation.
2. There is descending auditory pathway. That mainly innervate the outer hair cells that is
believed to influence and regulate the function of inner hair cells.(18)
3. There is high degree of combination between the auditory and visual pathway.
4. Auditory pathway have a connection with the reticular formation.
5. Tonotopic organization.(19)
6. Auditory pathway plasticity.(20)
3.4. Neural process of auditory information
The human auditory mechanism has a remarkable power to discriminate between the
sounds in the 60–20,000 Hz range. The basilar membrane is narrowest and stiffest at the base
of the cochlea (near the oval and round windows) and widest and most compliant at the apex
of the cochlea (near the helicotrema).

15. 15 |
Basilar membrane is a mechanical analyzer of source frequency. The basic pattern of
movement of the basilar membrane is that of a travelling wave. see figure (13).
The high frequency sound waves produce waves of maximum height near the oval
window, whereas low frequency sounds produce waves of maximum height near the
helicotrema.
Different hair cells respond to different frequencies of sound depending upon their
location on the basilar membrane.(21)
In auditory nerve, there is 30,000 nerve fiber, each group of these fibers innervate a
specific hair cells, and hence specific hair cells are stimulated by specific sound frequency,
then a specific group of auditory nerve fibers will be activated.
Encoding of the loudness occurring in at the level of cochlear nerve fiber by the
following mechanism:-
1- Increase in frequency of firing of an auditory nerve fiber.
2- Increase in number of nerve fiber stimulation
3- Stimulation of inner hair cells that are only sensitive to high loud sound.
It is also important to know that, the higher brain centers use the time lag between the
entries of sound to both ears as an indicator for the direction of sound.
4. Hearing loss
Hearing loss is partial or complete loss of sense of hearing that can be congenital or
acquired .
4.1. Types of hearing loss
Hearing loss is of three types :
1- Conductive hearing loss.
2- Sensorineural hearing loss (SNHL).
3- Mixed hearing loss.
4.1.1. Conductive hearing loss
Conductive hearing loss can happened due to any lesion that obstruct the conduction of
sound wave or serve to lower the acoustical energy.
Generally, any lesion that affect the external or middle ear components can result in
conductive hearing loss.

16. 16 |
Rarely, inner ear malformation and pathologies can result in conductive hearing loss (
e.g. large vestibular aqueduct )
Causes of conductive hearing loss include the following:-
1- Obstruction of external auditory canal by cerumen, debris or foreign bodies, swelling
of the lining of the canal, atresia or neoplasia in the canal.
2- Perforation of the tympanic membrane, this is either due to high loud sound, or by the
patient itself but the most common causes for tympanic membrane perforation is
Eustachin tube dysfunction that predisposed to acute otitis media ( AOM ) or serous
otitis media ( SOM ).(22)
Trauma, AOM, and chronic otitis media are usually the
predisposed factors for tympanic membrane perforation.
3- Cholesteatoma, a benign tumor composed of stratified squamous epithelial cells in
middle ear of mastoid, that could destroy the ossicles and normal ear tissues. It can be
due to metaplasia or irritation of the epithelia after chronic infection.
4- Ossicular pathology like otoseclrosis. Otoseclrosis is a slow progressive condition that
firstly affect the low-frequency sounds.
5- Presence of third window in the “inner ear“. This is a genetic condition that affect both
males and females and inherited as autosomal dominant trait with incomplete
penetrance.(23)
4.1.2. Sensorineural hearing loss (SNHL)
Sensorineural hearing loss (SNHL) can be caused by defects in transduction, neural
transmission and neural process of sound waves and signals. So, any damage to hair cells,
organ of corti or cochlea will lead to SNHL.
Causes of sensorineural hearing loss (SNHL) include:-
1. Intense noise
2. Viral infection
3. Ototoxic drugs
4. Fractures of temporal bone
5. Cochlear osteonecrosis
6. Meningitis
7. Meniere’s disease
8. Congenital malformation of inner ear
9. Presbyacusis : the most common cause of sensorineural hearing loss in adults.
10. Neoplastic diseases
11. Vascular diseases
12. Demyelinating or degenerative diseases
13. infectious disease
14. trauma affecting the central auditory pathways
15. Aging

17. 17 |
4.1.2.1. Presbyacusis ( presbycusis )
It is an age related condition, it is the most common cause of hearing loss in elderly
adults.(24)
It is characterized by symmetric high-frequency hearing loss and with progression,
it will involve all frequencies. The hearing impairment is associate with significant loss in
clarity. Presbycusis may be due to degeneration of organ of corti or cells in spiral ganglion.
Also it could happen due to atrophy of stria vascularis, a structure located in lateral wall of
endolymphatic duct that contain sodium-potassium ATP-dependent pumps, that are
responsible for production of endolymph, since stria vascularis is rich with capillaries.
4.1.2.2. Meniere’s disease (MD)
Meniere disease is a medical condition characterized by episodic vertigo, SNHL and
tinnitus. The pathophysiology of this disease is not well understood, but recent studies showed
that this disease is compatible with “ endolymphatic hydrops (EH) ” a condition involve the
distension of the endolymphatic sac and leakage of the membrane between the endolymph (
the potassium-rich fluid ) and the perilymph ( potassium-poor fluid ) secondary to trauma of
infection, resulting in disruption of the membrane potential of the hair cells in both the cochlear
and vestibular apparatuses.(25)
4.1.2.3. Noise-induced hearing loss (NIHL)
Noise-induced hearing loss is the most common cause of hearing loss in adults.(26)
there
is two types of this hearing impairment, acute acoustic trauma and gradually developing NIHL.
Acute acoustic trauma is a permanent cochlear damage result from exposure to excessive sound
pressure at one time, like explosions. Gradually developing NIHL is also a permanent cochlear
damage but it results from repeated exposure to high intensity sound.
Mechanical damage, ischemia and excitotoxicity are mainly responsible for noise-
induced cell death and biophysical changes in the cochlea. Auditory synaptopathy is an
additional consequence. Besides these cochlear pathologies, noise exposure leads to extensive
changes within the central auditory pathway. Overstimulation causes early cell loss in the
ventral cochlear nucleus just after noise exposure.(27)
4.1.3. Mixed hearing loss
A finding of conductive and sensory hearing loss in combination is termed mixed
hearing loss. Mixed hearing losses are due to pathology of both the middle and inner ear, as
can occur in otosclerosis involving the ossicles and the cochlea, head trauma, chronic otitis
media, cholesteatoma, middle ear tumors, and some inner ear malformations.

18. 18 |
4.2. Genetic causes of hearing loss
More than 40% of hearing impairments in childhood are hereditary.(28)
Hereditary
hearing impairment (HHI) could be syndromic or non-syndromic. Nearly two-thirds of HHIs
are nonsyndromic, and the remaining one third are syndromic. Between 70 and 80% of
nonsyndromic HHI is inherited in an autosomal recessive manner. Another 15–20% is
autosomal dominant. Less than 5% is X-linked or maternally inherited via the mitochondria.
The hearing genes are either structural proteins, transcription factors or gap junction proteins.
Generally, the hearing loss associated with dominant genes has its onset in adults, while
hearing loss associated with recessive genes are profoundly congenital. According to WHO,
60% of childhood hearing loss is due to preventable causes.(29)
Preventable causes of childhood
hearing loss include:
1- Infections such as mumps, measles, rubella, meningitis, cytomegalovirus infections,
and chronic otitis media (31%)
2- Complications at the time of birth, such as birth asphyxia, low birth weight, prematurity,
and jaundice (17%).
3- Use of ototoxic medicines in expecting mothers and babies (4%)
4- Others (8%)
4.3. Clinical approaching to a patient with hearing loss
The figure below summarizes how to approach to a patient with hearing loss.
Figure (14): An algorithm for the approach to hearing loss.(30)

19. 19 |
Clinical assessment of patient with hearing loss is via:-
1- Otoscopic examination
2- Tuning-fork testes
1- Otoscopic examination
It is a medical examination, using a device called “auriscope“, to look at the external
auditory canal and tympanic membrane. most of external ears and tympanic membrane defects
could be seen using this examine and label this as conductive hearing loss with no necessary
to do the Tuning-fork test. Figure (15) shows the structures that could be seen through normal
tympanic membrane.
Figure (15): normal tympanic membrane of
left ear.(31)
1- Umboo
2- Cone of light
3- Lateral process of malleus
4- Short process of incus
5- Pars flaccida
6- Pars tensa
2- Tuning-fork test
We use a 512 Hz or 256 Hz tuning fork to help differentiate between conductive and
sensorineural hearing loss.
In Webber’s test, we place the base of the vibrating tuning fork in the middle of the patient’s
forehead. The noise should be heard equally in both ears. The noise will be louder in the ear
with conductive hearing loss, while in SNHL, the noise will be heard well in the better-hearing
ear.
In Rinne’s test, we place the vibrating prongs at the patient”s external auditory meatusm,
then we ask if he can hear it.
After that, we place the still-vibrating base at the mastoid process, then ask the patient
where it was louder, in front or behind the ear. normally, air conduction is better than bone
conduction. In conductive hearing loss, bone conduction will be better than air conduction. In
SNHL, no noise will be heard at this ear at all.
1
2
3
4
5
6

20. 20 |
Laboratory assessment of patient compline of haring loss include audiologic
assessment, evoked response methods or radiological examination.
Audiologic assessment Evoked response Imaging
Pure tone audiometry Electrocochleography CT scan
Speech audiometry test Brainstem auditory evokes
response BEAR
MRI
Tympanometry vestibular-evoked myogenic
potential (VEMP)
---------------------------------
Figure (16): Laboratory assessment of hearing.
Pure tone audiometry is used to assess hearing acuity for specific tones. Usyally it used
to apply of a sound frequencies range from 250 Hz to 8000 Hz with a different intensities.
Responses will be presented in audiogram, which is a plot of intensity in decibels (dB) for the
hearing threshold versus frequency. Pure tone audiometry establishes the presence and severity
of hearing impairment, unilateral versus bilateral involvement, and the type of hearing loss.
Large mass components of conductive hearing loss produce elevation threshold that is
predominant in higher frequencies, while large stiffness components as in early otoseclrosis of
the stapes, will raise the threshold of low-frequency sounds.(30)
Conductive hearing loss
involving all frequencies suggests involvement of both masses and stiffness. SNHL, such as
presbyacusis involve mainly the high frequencies.
Tympanometry is used to measure the impedance or compliance of middle ear in
response to change in intensities. It is useful to detect middle ear effusion. Other techniques
are more complex and available only in special and very limited centers.
4.4. Treatment of hearing loss
Treatment and management of hearing loss is strongly dependent on the type, location
and severity of the condition.
Conductive hearing loss can be treated with surgical correction, for example if tympanic
membrane was perforated, then we can repair it surgically and thus, we get a better hearing.
Hearing aids, which are electrical devices used an electrical technique to amplify sound
may be useful in conditions with conductive hearing loss.
Patients with SNHL are regularly rehabilitated with hearing aids.(32)
Since the current
generations of hearing aids are very small and can be hidden inside the external auditory canal,
then they could not cause stigma associated with their use.

21. 21 |
Two important notes should be considered in hearing aids devices:-
1- As they amplify sound, these devices amplify sound of any source, so, noise as well as
normal speech will be amplified, and the absolute solution for this condition is to place
the microphone near the speaker, and this is not acceptable practically.
2- Although hearing aids can amplify sound, they could not restore the clarity of sound
that have been lost.
Some hearing aids composed of a microphone placed in the hearing-impaired ear with a
receiver placed in the contralateral normal hear. These devices called CORS (contralateral
routing of signals) hearing aids. There is also BAHA (bone anchored hearing aids) devices in
which they include the same technique that used in CROS devices except that the signals wilbl
transmitted from the impaired ear to the normal ear through vibrating of the skull.
Unfortunately, the CROS and BAHA do not restore hearing in deaf ear.(33)
There is many other modifications to hearing aids devices, but the main principle of action
is as mentioned above.
The only way to restore hearing in SNHL is through “cochlear implant”. There is specific
criteria for cochlear implant, this include severe to profound hearing loss with a sentence
cognition ≤ 40% under best aided condition.(34)
In most SNHL, there is degeneration of hair cells, but the ganglionic cells of the eighth
cranial nerve will be preserved. So stimulation of these cells can treat the hearing loss. Cochlear
implants, as shown in figure (17), is a technique used to stimulation of these cells.
Figure (17): a cochlear implant.(32)

22. 22 |
Cochlear implant technique is composed of microphone and a speech processor worn
on the ear and a receiver device that will implant under the temporalis muscle. The internal
receiver will be connected to electrode that will be implant on cochlea.
There is also a hybrid cochlear implant, in which this technique will treat only the high
frequency hearing loss. So, patients will normal low-frequency hearing and have a defect in
high-frequency hearing will get benefit from this technique. This means individuals with hybrid
cochlea use their own natural low frequency acoustic hearing and rely on the implant for
providing electrical high frequency hearing.(35)
For individuals who have had both eighth nerves destroyed by trauma or bilateral
vestibular schwannomas (e.g., neurofibromatosis type 2), brainstem auditory implants placed
near the cochlear nucleus may provide auditory rehabilitation.
4.5. Prevention
There is specific strategies that can be applied individually and even a prevention
programs that can be useful of the diseases at the level of society, these strategies and programs
may include the following:-
1- immunizing children against childhood diseases, including measles, meningitis, rubella
and mumps;
2- immunizing adolescent girls and women of reproductive age against rubella before
pregnancy;
3- preventing cytomegalovirus infections in expectant mothers through good hygiene;
screening for and treating syphilis and other infections in pregnant women;
4- strengthening maternal and child health programmes, including promotion of safe
childbirth;
5- following healthy ear care practices;
6- screening of children for otitis media, followed by appropriate medical or surgical
interventions;
7- avoiding the use of particular drugs which may be harmful to hearing, unless prescribed
and monitored by a qualified physician;
8- referring infants at high risk, such as those with a family history of deafness or those
born with low birth weight, birth asphyxia, jaundice or meningitis, for early assessment
of hearing, to ensure prompt diagnosis and appropriate management, as required;
9- reducing exposure (both occupational and recreational) to loud sounds by raising
awareness about the risks; developing and enforcing relevant legislation; and
encouraging individuals to use personal protective devices such as earplugs and noise-
cancelling earphones and headphones.

23. 23 |
5. Epidemiology
Around the world there is 360 million people (5.3%) affected with disabling hearing loss,
see figure (18).
Figure (18): Hearing loss: WHO global estimates.(2)
About (91%) are adults while the remaining (9%) are children. Males are slightly more
affected than females,(36)
see figure (19).
Figure (19): males and females adults, with children that affected with hearing
loss globally.(2)
Approximately one-third of persons over 65 years are affected by disabling hearing
loss.(37)
The prevalence of disabling hearing loss in children & elderly follow the same
geographical disturbances, see figure (20)
94.70%, 95%
5.30%, 5%
Normal population People with disabiling hearing loss (360M)

24. 24 |
Figure (20): Disabling hearing loss in population above 65 Years with
distribution all over the world.(2)
6. Summary
Disabling hearing loss is one of the most frequent sensory deficit in people. There is
different types of hearing loss, each type with a specific cause. Knowing the type, location and
severity of the condition is of high important in treatment and management of the cases.
There is 360 million people around the world affected with this condition. Both congenital and
acquired conditions could be prevented.

25. 25 |
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