Hearing Disorders

Front 1

Classification

Back 1

In pediatric age we have two major classifications based on:

The relation with the language development:

- PRE-LINGUAL deafness if before 18 mo: it determines a complete impairment of speech abilities

- PERI-LINGUAL if between18 mo ÷ 36 mo: it causes a partial to complete deficit of the acquired verbal language

- POST-LINGUAL after 36 mo: Post-lingual usually determines a slight impairment

The relation with the timing of the causative factors:

Hereditary and Acquired hearing loss.

Acquired can be subdivided based on the timing of birth:

PRE-NATAL - before birth

PERI-NATAL - during birth

POST-NATAL - after birth

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Relation between hearing and language development

Back 2

The relation of language development, the degree of hearing loss and the affected side are very important, because it relates to the ability of the newborn/infant to develop communication skills.

In particular the degree of hearing loss comprises:

MILD: 20÷40 dB HL

MODERATE: 40÷70 dB HL

SEVERE: 70÷90 dB HL

PROFOUND: 90÷120 dB HL

TOTAL: > 120 dB HL !

So a pre and a peri-lingual hearing loss - a patient with a degree of HL that’s moderate or higher and a bi-lateral HL is characterized by a severe impairment of language development.

Brain involution after 12 months

- Reduction of ganglion spiral cells & cochlear nucleus cells

- Reduction of cortical synapses (cortico-cortical & corticothalamic)

- Primary dendrites reduction of cortical pyramidal neurons

- Colonization of the deprived cortical hearing areas from visual & somatosensory areas

Front 3

Early diagnosis

Back 3

An early diagnosis allows a correct hearing and speech rehabilitation that should be performed from 6 mo because at this age the development of language ability is similar to normal hearing at 4 yrs of age!

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Bilateral Pre-lingual Sensorineural Hearing Loss

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EPIDEMIOLOGY

• 1 in 1000 newborns

• Most frequently: SEVERE hearing loss

• HEREDITARY HEARING LOSS (60%):

- Congenital form

- Later-onset form

• ACQUIRED HEARING LOSS (40%)

ETIOLOGY

• Hereditary:

- Autosomal-recessive (70%)

- Autosomal-dominant (25%)

- Sex-linked (<5%)

- Mitochondrial (<1%)

Front 5

BPSHL: Non-syndromic forms

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Non-syndromic (70%) -> about 150 loci related with genetic hearing loss. The one which must be kept in mind is GJB2, ENCODING FOR CONNEXIN 26 , a gap junction protein.

Front 6

Acronym for the syndromes

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Al PortO tRe Cervelloni, (Ward, End e Burg) Prendon Sticker delle Tre Colline di casa Usher.

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BPSHL: Syndromic forms -> ALPORT

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aka Hereditary nephritis:

- AR / X-linked

- Chronic nephritis with blood in the urine

- Ophthalmic features -> posterior subcapsular cataract

- Type IV collagen network is involved; it is a protein present in the basement membrane.

- Deafness occurs later, not at birth

Front 8

BPSHL: Syndromic forms -> Branchio-Oto-Renal

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- AD

- Congenital, early onset

- Branchial cysts or fistulae -> malformation of external ear

- Kidney dysfunction -> bilateral renal hypoplasia

- External/Middle/Inner ear -> Enlarged vestibular aqueduct syndrome. The vestibular aqueduct is a bony canal that contains the endolymphatic duct, linking the endolymphatic sac with the utricle and saccule. The endolymphatic sac is important to obtain absorption of endolymphatic fluids.

Clinically:

o Sudden hearing loss (usually after a slight temporal bone trauma or barotrauma) or Fluctuating hearing loss (quite similar to Menière disease)

o Progressive hearing loss

o Vestibular symptoms (Menière disease type)

Front 9

BPSHL: Syndromic form -> Jervell-Lange-Nielsen

Back 9

- AR

- Congenital, early onset

- Prolonged QT interval

Front 10

BPSHL: Syndromic form -> Pendred

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- AR

- Congenital, early onset

- The most frequent cause of bilateral sensorineural hearing loss in scholar age

- Thyroid dysfunction -> Goiter

- Enlarged vestibular aqueduct

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BPSHL: Syndromic form -> Stickler

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- AD

- Congenital, early onset

- Bird facies:

Cleft Palate

Glossoptosis -> if upper airways obstruction, submit to tracheotomy

Micrognathia -> external and middle ear malformations are often related to mandibular malformations since they originate from the same branchial arch (I-II). The inner ear derives from the auditory placode, different.

- Joint anomalies

- Ophthalmopathy

Front 12

BPSHL: Syndromic form -> Treacher-Collins-Franceschetti

Back 12

- AD

- Congenital, early

- External/Middle ear anomalies -> microtia/anotia

- Bird facies

- Mandibulofacial dysostosis

Front 13

BPSHL: Syndromic form -> Usher syndrome

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- AR

- Congenital, early onset

- Associated with retinitis pigmentosa

- These patients are deaf, blind and as a consequence have important unbalance problem

Front 14

BPSHL: Syndromic form -> Waardenburg syndrome

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- AD

- Congenital, early onset

- White forelock

- Heterochromia iridum

- Telecanthus (dystopia canthorum)

This syndrome is not of easy diagnosis because heterochromia iridis is usually not considered as a sign of a pathology, white forelock are usually dyed by the hair dresser (so you don’t see it..), so you have only the deafness as a sign!

Front 15

BPSHL: Others

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Charge syndrome

COLOBOMA

HEART DEFECT

ATRESIA OF CHOANAE

RETARDED GROWTH

GENITAL HYPOPLASIA

EAR ANOMALIES (microtia, cochlear hypoplasia)

Down Syndrome

Inner ear malformation and tubal muscles malfunction → mixed hearing loss

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Acquired Hearing Loss: pre-natal

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Two main causes:

• INFECTIONS

• DRUG TOXICITY

o INFECTIONS

• RUBELLA: cochlear hearing loss + pulmonary stenosis, mental retardation, microphthalmia (“Rubella Syndrome”)

• TOXOPLASMOSIS: inflammatory damage to the inner ear

• CONGENITAL SYPHILIS: progressive degeneration of the inner ear and the peripheral neuron associated with interstitial keratitis and dental defects

• CYTOMEGALOVIRUS

• HERPES SIMPLEX

o DRUG TOXICITY

• QUININE

• AMINOGLYCOSIDES

• THALIDOMIDE +

• ALCOHOL

Front 17

Acquired Hearing Loss: peri-natal

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• METABOLIC

• OBSTETRIC TRAUMA

o METABOLIC

• KERNICTERUS (PERINATAL HYPERBILIRUBINEMIA SYNDROME): athetoid cerebral palsy and sensorineural hearing loss (Rh- incompatibility, massive deposits of bilirubin in the cochlear centers and occasionally in the cochlea itself with corresponding cochleoneural deafness

• PERINATAL HYPOXIA: injury to the cochlea and its centers in the brainstem

o OBSTETRIC TRAUMA

• FORCEPS

• INTRACEREBRAL HEMORRHAGE

• INTRACOCHLEAR HEMORRHAGE

Front 18

Acquired Hearing Loss: post-natal

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o INFECTIONS

• MENINGITIS & MENINGOENCEPHALITIS: labyrinthitis and cochleovestibular neuritis with damage to the sensory cells and peripheral neurons; central lesions

• MUMPS: cochlear and neural lesions

• MEASLES: degeneration of the cochlea and its peripheral neurons due to infective damage, serous labyrinthitis.

• OTITIS MEDIA

Front 19

Diagnosis

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Medical History

1. ACQUIRED CAUSES vs HEREDITARY CAUSES (familiarity!)

2. Visual disorders; deambulatory problems ( -> Usher Syndrome)

3. Hematuria ( -> Alport Syndrome); Renal disorders ( -> BOR Syndrome)

4. White forelock; Heterochromia iridis ( -> Waardenburg Sd.)

5. Goiter ( -> Pendred Sd.)

Physical examination:

- Neck (branchial cysts or fistulae; goiter)

- External ear

Instrumental examination

- Urine tests -> Alport Syndrome, BOR syndrome

- Ophtalmic evaluation -> Alport Syndrome, Stickler syndrome, Usher Syndrome

- Elettrocardiogram -> Jervell-Lange-Nielsen Syndrome

- CT scan -> only after 3-4 years of age

Front 20

Cochlear implant

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Subcutaneously implanted device that can transform sound waves into electrical impulses that directly stimulate the cochlear nerve with intracochlear electrodes.

To perform the cochlear implant surgery first of all we perform an retro-auricular skin incision, we find the different layers, among which there is the Temporalis fascia (that is used to reconstruct the tympanic membrane when there are some perforations), then we find the Mastoid tip and the external auditory canal.

Then we perform a mastoidectomy in which we conserve the posterior wall of the auditory canal, drilling along the base of the temporal muscle and the posterior wall of the external auditory canal. We arrive to see the lateral semicircular canal and the incus. At this point we perform a posterior tympanotomy and to be careful to the Fallopian canal and the Facial nerve and this make it a difficult surgery; we do this to reach the Round window. “What do you have to do with the facial nerve?” We have to preserve it.

Front 21

Auditory brainstem test

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I, II for cochlear nerves

III for cochlear nucleus

IV for superior olive

V for lateral lemniscus

VI and VII mediale geniculate bodies

Front 22

Otoacustic emissions

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Evoked OAEs EditEvoked otoacoustic emissions are currently evoked using three different methodologies. Stimulus Frequency OAEs (SFOAEs) are measured during the application of a pure-tone stimulus, and are detected by the vectorial difference between the stimulus waveform and the recorded waveform (which consists of the sum of the stimulus and the OAE). Transient-evoked OAEs (TEOAEs or TrOAEs) are evoked using a click (broad frequency range) or toneburst (brief duration pure tone) stimulus. The evoked response from a click covers the frequency range up to around 4 kHz, while a toneburst will elicit a response from the region that has the same frequency as the pure tone.