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)

The Auditory Ossicles
Suspended from the roof of the middle ear cavity and connect the tympanic membrane with the oval window
Connected by synovial joints; covered with the epithelial lining of the cavity
The malleus (“hammer”) has its handle firmly fixed to the upper portion of the tympanic membrane
The head of the malleus articulates with the incus (“anvil”), which articulates with the stapes (“stirrup”)
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
Barotrauma
Injury resulting from the inability to equalize the barometric stress on the middle ear
Otitis media (OM)
An infection of the middle ear that is associated with a collection of fluid
Otosclerosis
The formation of new spongy bone around the stapes and oval window, which results in progressive deafness
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
Sensorineural Hearing Loss
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
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
Ménière’s disease: these signals are unbalanced by unilateral involvement of one of the vestibular organs
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
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 (i.e., nystagmus) and muscle control of balance and equilibrium often are used
Diagnostic Tests of Vestibular Function
Electronystagmography
Caloric Stimulation
Rotational Tests
Romberg Test