Chapter 55 Disorders of Hearing and Vestibular Function

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)

Causes of Disorders of the External Ear Impacted cerumen Inflammation (otitis externa) Drainage from the external ear (otorrhea)

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

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

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.

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

Treatment of Hearing Loss Simple removal of impacted cerumen Hearing aids Cochlear implants Reconstruction of the tympanic membrane Special consideration for children

Question Which of the following explains why infants are more susceptible to acute otitis media? Poor hygiene Kids will usually put things in their ears The infant ear canal is smaller The eustachian tube is shorter

Answer Poor hygiene Kids will usually put things in their ears The infant ear canal is smaller 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.

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

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

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

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

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.

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

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.

Question Is the following statement true or false? Nystagmus is an abnormal condition.

Answer False: Normal eye adjustments are considered nystagmus, but some pathological nystagmus does occur.