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Chapter 55
Disorders of Hearing and
Vestibular Function
Copyright © 2009 Wolters Kluwer Health | Lippincott Williams & Wilkins
Structure of the Ears
• External and middle ear
– Function in capturing, transmitting, and amplifying
sound
• Inner ear
– Contains the receptive organs that are stimulated by
sound waves (hearing) or head position and
movement (vestibular function)
Copyright © 2009 Wolters Kluwer Health | Lippincott Williams & Wilkins
Causes of Disorders of the External Ear
• Impacted cerumen
• Inflammation (otitis externa)
• Drainage from the external ear (otorrhea)
Copyright © 2009 Wolters Kluwer Health | Lippincott Williams & Wilkins
Three Basic Functions of the Eustachian
Tube
• Ventilation of the middle ear, along with equalization of
middle ear and ambient pressures
• Protection of the middle ear from unwanted
nasopharyngeal sound waves and secretions
• Drainage of middle ear secretions into the nasopharynx
Copyright © 2009 Wolters Kluwer Health | Lippincott Williams & Wilkins
Disorders of the Middle Ear and
Eustachian Tube
• Acute otitis media in children
– The eustachian tube is shorter, more horizontal, and wider
– Infection can spread more easily through the eustachian
canal of infants who spend most of their day in the supine
position.
• Otitis media (OM)
– An infection of the middle ear associated with a collection
of fluid
• Otitis media with effusion
– The presence of fluid in the middle ear without signs and
symptoms of acute ear infection
Copyright © 2009 Wolters Kluwer Health | Lippincott Williams & Wilkins
Disorders of the Middle Ear and
Eustachian Tube (cont.)
• Otosclerosis
– The formation of new spongy bone around the stapes
and oval window, which results in progressive
deafness
– Bone increasingly immobilizes the stapes, reducing
the transmission of sound
– Pressure on middle ear structures or the
vestibulocochlear nerve may contribute to the
development of tinnitus, sensorineural hearing loss,
and vertigo.
Copyright © 2009 Wolters Kluwer Health | Lippincott Williams & Wilkins
Disorders of the Inner Ear
• Tinnitus
– The perception of abnormal ear or head noises, not
produced by an external stimulus
• Hearing loss (qualified as mild, moderate, severe, or
profound)
– Conductive hearing loss
• Stimuli are not adequately transmitted
– Sensorineural hearing loss
• Disorders that affect the inner ear, auditory nerve,
or auditory pathways of the brain
– Mixed hearing loss
Copyright © 2009 Wolters Kluwer Health | Lippincott Williams & Wilkins
Treatment of Hearing Loss
• Simple removal of impacted cerumen
• Hearing aids
• Cochlear implants
• Reconstruction of the tympanic membrane
• Special consideration for children
Copyright © 2009 Wolters Kluwer Health | Lippincott Williams & Wilkins
Question
• Which of the following explains why infants are more
susceptible to acute otitis media?
a. Poor hygiene
b. Kids will usually put things in their ears
c. The infant ear canal is smaller
d. The eustachian tube is shorter
Copyright © 2009 Wolters Kluwer Health | Lippincott Williams & Wilkins
Answer
a. Poor hygiene
b. Kids will usually put things in their ears
c. The infant ear canal is smaller
d. The eustachian tube is shorter: It is also more
horizontal and wider, and with infants lying on their back
most of the time, it is easy for the infection to spread.
Copyright © 2009 Wolters Kluwer Health | Lippincott Williams & Wilkins
Balance Reflexes
• Vestibular nuclei
– Integrative center for balance
– Receive input from visual and somatic receptors
• CN III, IV, and VI
– Reflex movements of the neck, limb
• Vestibulo-ocular reflexes
– Trunk muscles
Copyright © 2009 Wolters Kluwer Health | Lippincott Williams & Wilkins
Nystagmus
• The involuntary rhythmic and oscillatory eye movements
that preserve eye fixation on stable objects in the visual
field during angular and rotational movements of the
head
– Initiated by impulses generated by the movement of
the endolymph in the semicircular ducts
– Transmitted to the vestibular nuclei and relayed to
the appropriate extraocular motor nuclei for
controlling conjugate eye movement
Copyright © 2009 Wolters Kluwer Health | Lippincott Williams & Wilkins
Disorders of Vestibular Function
• CNS lesions involving the cerebellum and lower brain
stem
• Vertigo
– An illusion of motion occurs
– The person may be stationary and the environment in
motion (objective vertigo) or the person may be in motion
and the environment stationary (subjective vertigo)
• Motion sickness
– A form of normal physiologic vertigo
– Caused by repeated rhythmic stimulation of the vestibular
system, such as is encountered in car, air, or boat travel
Copyright © 2009 Wolters Kluwer Health | Lippincott Williams & Wilkins
Disorders of Peripheral Vestibular
Function
• The peripheral vestibular system consists of a set of paired inner ear
sensory organs, each sending messages to brain centers that
interpret signals related to the body’s position in space and control
eye movement.
–
Benign paroxysmal positional vertigo: these signals are
distorted
• Sudden onset of dizziness or vertigo provoked by certain
changes in head position
–
Ménière’s disease: these signals are unbalanced by unilateral
involvement of one of the vestibular organs
• Fluctuating episodes of tinnitus, feelings of ear fullness, and
violent rotary vertigo that often renders the person unable to
sit or walk
Copyright © 2009 Wolters Kluwer Health | Lippincott Williams & Wilkins
Possible Causes of Ménière’s Disease
• Trauma
• Infection (e.g., syphilis)
• Immunologic
• Endocrine (adrenal-pituitary insufficiency and
hypothyroidism)
• Vascular disorders have been proposed as possible
causes of Ménière’s disease.
Copyright © 2009 Wolters Kluwer Health | Lippincott Williams & Wilkins
Central Causes of Vertigo
• Abnormal nystagmus and vertigo can occur as a result of
CNS lesions involving the cerebellum and lower brain
stem
• Brain stem ischemia
• Tumors
• Multiple sclerosis
Copyright © 2009 Wolters Kluwer Health | Lippincott Williams & Wilkins
Basis for Diagnosis of Vestibular
Disorders
• A description of the symptoms
• A history of trauma or exposure to agents that are
destructive to vestibular structures
• Physical examination
– Tests of eye movements (e.g., nystagmus) and
muscle control of balance and equilibrium often are
used.
Copyright © 2009 Wolters Kluwer Health | Lippincott Williams & Wilkins
Question
Is the following statement true or false?
• Nystagmus is an abnormal condition.
Copyright © 2009 Wolters Kluwer Health | Lippincott Williams & Wilkins
Answer
• False: Normal eye adjustments are considered
nystagmus, but some pathological nystagmus does occur.
Copyright © 2009 Wolters Kluwer Health | Lippincott Williams & Wilkins