Hearing Disorders in Children

Key Points

Week 3 - Beginning of the auditory system forming
Week 7-8 - Semicircular canals form
Week 25 - Cochlea is adult like
Until the end of gestation - ME continues to develop

There are many pathological conditions that cause hearing disorders in childhood, including disease, trauma and developmental disturbance
Some hearing disorders are unique to childhood: others impact children to a greater or lesser extent than they do adults
Conductive hearing disorder results from problems involving structures of the outer and middle ear, including congenital anomalies and otitis media and its complications
Sensory hearing disorder results from problems involving the cochlea, including congenital inner ear anomalies, maternal infections, such as cytomegalovirus and toxoplasmosis, and acquired infections, such as meningitis and mumps
Neural hearing disorder results from problems involving the auditory nervous system, including neoplasms and hypoxia
The impact of hearing disorder on speech and language development varies as a function of degree, type, configuration and stability of hearing loss and when in the course of development hearing loss occurs

A hearing disorder results from a disruption in function in structures that transmit an acousitc signal from the outer ear to the point of perception in the brain
In most cases, the impacts on hearing sensitivity and suprathreshold perception are predictable from the nature of the pathology
As many as 3 in 1000 infants are born with congenital bilateral sensorineural hearing loss
Permanent sensorineural hearing loss in at least one ear is closer to 8 in 1000 infants
Transient conductive disorder, as many as 15 in 1000 infants have some degree of hearing disorder
The more severe the hearing disorder, the more likely it will be to affect normal speech and language acquisition
Interacting with type and severity of the disorder is the age of onsent
Some are present at birth or are congenital; others occur after birth or are acquired
A hearing disorder can occur before (prenatal), during (perinatal), or after (postnatal) birth
- Prenatal disorders are typically caused by abnormal embryological development
The outer and inner ear systems develop primarily from the ectodermal tissues; the middle ear components from the mesodermal layer
Development of the auditory system begins in the third week of gestation, while the middle ear continues to develop until the end of gestation
Other body systems that are undergoing similarly critical development may also be affected, resulting in a constellation of symptoms known as a syndrome
Exogenous etiologies, which have factors that are not necessarily intrinsic to the genetic makeup of the individual
Endogenous conditions which are inherited

Nature of Conductive Hearing Disorders

Attenuation of sound as it travels from the outer ear to the cochlea
When the middle ear mechanism is involved, its important function as an impedance-matching transformer of acoustic air pressure waves to fluid motion in the cochlea is like-wise disrupted
A pathologic condition that affects the physical mass of the outer and middle ear mechanism will reduce sensitivity to higher-frequency sound
One that affects the stiffness will reduce sensitivity to lower-frequency sound
Perception of loudness, differential thresholds for pitch and loudness, temporal processing and speech recognition ability are all normal at suprathreshold levels
Conductive hearing disorders in children are most commonly acquired and transient
Congenital disorders which are primarily caused by structural deformities or anomalies, can cause significant conductive hearing loss and may not be readily treatable until the child is older
Recurrent middle ear disorder and resultant fluctuating hearing sensitivity appear to be prone to suprathreshold hearing disorder and language/learning problems

Acquired Prenatal Conductive Disorders

Atresia is the absence of an opening of the ear or external auditory meatus
Bony atresia is the congenital absence of the ear canal caused by a wall of bone separating the external ear from the middle ear.
Membranous atresia is the absence of a canal caused by a dense soft tissue plug obstructing the canal
Atresia is unilateral in 70-85% of cases
Atresia can cause maximum conductive hearing loss (~60dB) depending on the density of the blockage
Abnormally small or malformed ear is known as microtia
Stenosis or narrowing of the ear canal

Middle Ear Anomalies

Ossicular dysplasia, fenestral malformations and congenital cholesteatoma

Causes of Prenatal Outer and Middle Ear Anomalies

Congenital outer and middle ear anomalies are often a result of genetic causes
Often, prenatal outer and middle ear anomalies may occur with other craniofacial anomalies and/or sensorineural hearing loss

Acquired Postnatal Conductive Disorders

Otitis Media with Effusion

Otitis media is a general term to descrive inflammation of the middle ear mucous membrane and tympanic menbrane
76 to 95% of all children have one episode of otitis media by 6 years of age
60% of those children who have otitis media before the agte of 1 year will have six or more bouts within the ensuing 2 years
Risk factors for otitis media include young age, Native American or Inuit heritage, anatomic defects, exposure to smoke in the household, male sex, crowded living conditions, poor sanitation, inadequate medical care, eating in prone position, obesity and day care
Otitis media is usually caused by eustachian tube dysfunction secondary to upper respiratory tract infection
The fluid may be referred to as serous (thin, watery, sterile), suppurative (containing pus), purulent (suppurative), mucoid (thick, viscid), and sanguineous (containing blood). Adhesive otitis media involves severe retraction of the tympanic membrane into the middle ear space
Acute otitis media with effusion is the term describing rapid onset of symptoms of middle ear inflammation, including redness of the tympanic membrane and otalgia
- it is usually referred to as acute if it lasts fewer than 3 weeks: subacute if it lasts fewer than 3 months
Recurrent OME consists of repeated episodes of acute otitis media with normal middle ear examinations between episodes
Persistent middle ear effusion is an asymptomatic effusion that persists following treatment for acute OME
The term chronic OME is used to describe a condition that lasts longer than 3 months
Chroni suppurative otitis media is a chronic infection of the middle ear and mastoid with a perforation of the tympanic membrane and otorrhea
OME may resolve spontaneously or may require treatment with antibiotics or pressure-equalization tubes
Untreated OME can lead to several complications including cholesterol granuloma, adhesive otitis media, facial paralysis, labyrinthitis, acute mastoiditis, petrositis, meningitis, signoid sinus thrombosis...
Among the more common complications are tympanic membrane perforation, tympanosclerosis and cholesteotoma

Complications of Otitis Media with Effusion

The tympanic membrane may become perforated as a result of OME because of increased pressure from fluid in the middle ear space, or it may be perforated from barotrauma, trauma, myringotomy or tympanosomy tube placement
Tympanosclerosis is a degerneration of collagenous fibrous tissues of the tympanic membrane and is a common sequela of OME
Cholesteatomas are cysts that contain keratinizing squamous epithelium and are found in the middle ear, mastoid, external auditory canal, or petrous bone
- Average air bone gaps are estimated to be 30 to 38 dB

Excessive Cerumen

an accumulation of ear wax in the ear canal
A high-frequency conductive hearing loss can occur when the ear canal is 80 to 95% occluded. A low-frequency conductive loss occurs with total occlusion of the ear canal

Otitis Externa

Otitis externa is the broad term for inflammation or infection of the external auditory canal and auricula
Otitis externa rarely causes a hearing disorder
Acute diffuse otitis externa, also known as swimmers ear is one example of otitis externa
- It is a bacterial infection that causes itching, tenderness and pain and may include hearing loss and aural fullneess as the external auditory canal decreases in size with swelling

Sensory Hearing Disorders

Sensory disorders can occur from any number of changes in cochlear structure and function
The most vulnerable structures seem to be the outer hair cells of the organ of Corti which are responsible for the exquisite sensitivity and fine-tuning of the cochlea
Sensorineural hearing loss is usually permanent, although it can fluctuate in some cases and may be treatable in others

Causes of Sensory Hearing Disorders

Acquired Prenatal Sensory Disorders
Inner ear Anomalies

Inner ear malformations occur when development of the membranous and/or bony labyrinth is arrested during fetal development
Inner ear malformations can be divided into those in which both the osseous and membranous labyrinths are abnormal and those in which only the membranous labyrinth is abnormal
MRI has become a useful tool for imaging of the soft tissue structures
Included in the malformations of both membranous and osseous labyrinths are complete labyrinthe aplasia, common cavity defect, cochlear aplasia and hypoplasia and Mondini defect
- Common-cavity malformation comprises about one-fourth of all cochlear malformations
Cochlear aplasia is a rare malformation consisiting of conplete absence of the membranous and osseous cochlea and no auditory function, but presence of semicircular canals and vestibule
Cochlear hypoplasia is a malformation in which less than one full turn of the cochlea is developed
Mondini malformation is an incomplete partition of the cochlea
Hearing loss is usually progressive profound and bilateral
The Bing Siebenmann malformation is a rare malformation that results in complete lack of development of the membranous labyrinth
Scheibe aplasia is a common inner ear abnormality in which there is failure of the organ of Corti to develop fully, collapse of the cochlear duct, adherence of the bestibular membrane to the limbus, and degeneration of the stria vascularis
Alexander aplasia is an abnormal development in the remainder of the cochlea, resulting in low-frequency residual hearing

Cytomegalovirus

Is the largest known member of the human herpesvirus family and is the most common fetral viral illness
Other findings include microcephaly, petechiae (small purple spots on a body surface), intrauterine growth retardation, enlargement of the liver and spleen and inflammation of the choroid and retina
Hearing loss is of variable severity and can be bilateral or unilateral
The most commonly found configuration is flat

Congenital Syphillis

bacterial infection that is transmitted from mother to fetus in utero or through contact with a genital lesion during delivery
Hutchinson's triad: small notched teeth; hearing loss; and interstitial keratitis
Typical hearing loss is a rapid symmetric progression from high-frequency sensory loss to complete bilateral deafness
Vestibular function may also be severely affected
The Hennebert sign, in which nystagmus is observed as a result of pressure applied to the external auditory canal, is often found in otosyphilis

Maternal Rubella

occurs when an infected mother transmits the rubella virus to the fetus
Congenital rubella syndrome or Gregg syndrome includes a wide variety of defects, usually affecting haring, vision and heart function and often involving mental retardation and microencephaly

Toxoplasmosis

An infection caused by the parasite Taxoplasma gondii
Most newborns (70-90%) infected with congenital toxoplasmosis are asymptomatic at birth, up to 80% of these children develop sequelae later in life
Those who are symptomatic often have a classic triad of choriortinitis, intracranial calcifications, and hydrocephalus
The resulting disorder is a sensory or neural hearing loss that may range from mild unilateral loss to bilateral deafness

Acquired Perinatal and Postnatal Sensory Disorders

Persistent Pulmonary Hypertension of the Newborn/Extracorporeal Membrane Oxygenation

PPHN also known as persisten fetal circulation is a condition wherein the infant's blood flow bypasses the lungs, thereby eliminating oxygen supply to the organs of the body

Meningitis

Meningitis is an inflammation of the mebranes that surround the brain and spinal cord
- bacterial, aseptic and viral
The greatest frequency of hearing loss occurs in cases of bacterial meningitis
Most involvement is though to be cochlear but central auditory involvement may occur in some individuals
Cochlear osteoneogenesis or bony growth in the cochlea, may occur following meningitis, complicating possible cochlear implanatation

Autoimmune Inner Ear Disease

AIED is a syndrome of potentially reversible, bilateral, rapidly progressive and often fluctuating sensory hearing loss that may be associated with vestibular symptoms mimicking Meniere's disease

Viral Infection

Mumps is a viral infection that attacks a variety of organs, especially the salivary glands
Measles is a highly contagious viral illness that characteristically causes symptoms of rash, cough, fever, conjunctivitis, photophobia and Koplik spots
- hearing loss is a common commplication of measles

Ototoxicity

Ototoxicity is hearing loss from the toxic effects of drugs on the inner ear
Aminoglycoside antibiotics (streptomycin, gentamicin, dihydrostreptomycin, neomycin, kanamycin, erythormycin and vancomycin) loop diruetics, antineoplastic agents, salicylates and antimalarial drugs (quinine) can all damage the cochlea

Neural Hearing Disorders
Nature of Neural Hearing Disorders

Neural hearing disorders tend to be divided into two groups: retrocochlear disorders and auditory processing disorders
When a disorder is caused by an active, measurable disease process, such as a neoplasm or from damage caused by trauma or stroke, it is often referrred to as a retrocochlear disorder
That is, retrocochlear disorders result from structural lesions of the nervous system
when an impairment is due to developmental disorder or delay, it is often referred to as an auditory processing disorder; APD
That is, APDs result from functional lesions of the nervous system
The most common symptom of neural hearing disorder is difficulty extracting a signal of interest from a background of noise

Auditory Neuropathy Spectrum Disorder

operationally defined based on a constellatoion of clinical findings which varies as a function of age
In older children, auditory neuropathy is defined by an absent auditory brainstem response (ABR), poor speech perception, varying levels of hearing sensitivity loss, absence of acoustic reflexes and a preservation of some cochlear function as evidenced by the preservation of otoacoustic emissions (OAEs) and/or cochlear micrtophonics
In infancts, auditory neuropathy is defined by absent ABR and preserved OAEs and/or cochlear microphonics
it is becoming apparent that the term auditory neuropathy, as it is defined clinically, may represent at least two fairly different disorders, one sensory and the other neural
The auditory neuropathy of sensory origin (ANS) is probably a sensory hearing disorder that represents a transduction problem, with the failure of the cochlea to transmit signals to the auditory nerve
- The most likely origin of ANS is the inner hair cells
ANN was first described as a specific disorder of the auditory nerve that results in a loss of syncrony of neural firing; it is also referred to as auditory dys-synchrony
The cause of auditory neuropathy is often unknown
The age of onset is usually before ten years

Other Neural Hearing Disorders

Neoplasm

tumors of the posterior fossa in children are less likely to be acoustic schwannoma and more likely to be intrinsic tumors, such as gliomas and medulloblastomas
these benign tumors of the cerebellopontine angle affect the auditory system when they impinge on the eighth cranial nerve.

Hydrocephalus

the mos common finding is one of neuromaturational delay of the auditory system as measured on the ABR
This is usually due to enlarged ventricles and is not associated with permanent changes in auditory function

Hypoxia

deficiency in the amount of oxygen in the body

Hyperbilirubinemia

an excess of bilirubin in the blood that can be caused by many factors