Chapter 55 Disorders of Hearing and Vestibular Function

1. Chapter 55Disorders of Hearing and Vestibular Function

2. 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)

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

4. 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

5. 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

6. 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.

7. 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

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

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

10. 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.

11. 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

12. 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

13. 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

14. 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

15. 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.

16. 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

17. 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.

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

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