Transcript Auditory Nerve Disorders and Central Auditory Pathways

Central Auditory Nervous
System Disorders
Lecture 16
Auditory Nerve Pathways
 Nerve fibers pass from cochlea through 4
relay stations before auditory cortex ---
VIIIth Nerve
Tumors
 Acoustic Neuroma – slow
growing, benign tumor
 Incidence: 1/100,000
 Location: VIIIth nerve fibers pass through a bony
canal, from the inner ear to BS called the internal
auditory canal (IAC)
Acoustic Neuromas
 Small (less than 1.5 cm)
 Medium (1.5 cm to 2.5 cm)
 Large (more than 2.5 cm)
Patient Characteristics
 Onset from 30-50 years of age
 55% female/ 45% male
 95% unilateral
Clinical Course
 Symptoms arise from compression, atrophy
and invasion of auditory and vestibular nerve
 1st symptom: unilateral SNHL, becomes
progressive
 Tinnitus
 Dizziness, unsteadiness
 Pressure in affected ear
 With increased size of tumor may present
with headaches, dysphagia, dysarthria etc.
 Other cranial nerves may be involved
Differential Diagnosis
 MRI or C/T Scan
 Vestibular Tests
 Audiometric Battery:
 PTA:
 Sp.Recognition
 Tympanogram:
 OAE’s:
 ABR:
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
I-V
Threshold where wave V observed
Treatment
 Observation
 Repeat audiological evaluations
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Amplification
 Surgical Removal: Partial
Total
 Radiation
Multiple Sclerosis (MS)
 Degenerative autoimmune disease of CNS
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Plaques develop and result in demyelination
Onset in early adulthood 20-40
Caucasians 2x more likely than other ethnic
groups
Genetic influence:
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1/1000
If family hx, 3/100
 Hearing problems
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HL uncommon @6 %
40%w audios WNL report difficulty hearing in
BN
MS
 PTA:
 Sp Recognition:
 Tympanogram:
 OAE:
 ABR:
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
I-V
Lowest level wave V threshold
Neurofibromatosis
 Genetic disorder of the nervous system that
affects development of neural cells
 Causes dozens of neuromas in internal
auditory canal
 Causes skin changes and bone deformities
 New cases without a genetic cause can arise
 Present with bilateral SNHL
 Two types
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NF1
NF2
NF 1
 NF1: Autosomal Dominant
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changes in skin appearance, Café au lait
spots
Non cancerous tumors develop under the skin,
around eyes, spinal cord
Symptoms evident at birth or during infancy
and almost always by the time a child is about
10 years old
Incidence 1/4000
NF 2
 NF2 : AD
 Bilateral tumors on the VIII th cranial nerve
 Tumors cause pressure damage to other
cranial nerves – more often affect hearing
 HL as early as the teen years
 Headache, tinnitus, often affects the eyes
 Incidence; 1/33,000
Treatment
 Control of symptoms
 Surgical removal

Risk of regrowth
 Genetic testing
 NF2 – Auditory
Brainstem Implant
Auditory Neuropathy/Auditory
Dysynchrony (AN/AD)
 Describes a condition where client has
normal hair cell function, but abnormal neural
function
 “Synchrony” disorder within the spiral
ganglion cells or the auditory nerve BEFORE
it enters the brainstem
 Can co-exist with any degree of hearing
impairment (mild – mod)
Estimates of Incidence
 No clear cause
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Jaundice, LBW, prematurity, inadequate
supply or oxygen
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10% of children who have been in the NICU
0% of children who have been in the well baby
nursery
Can co-occur with other disorders
 Charcot-Marie Tooth – Motor & sensory nerves
 Friedreich’s Ataxia - vision, HL, and slurred speech
Characteristics
 No single entity, patient variation
 Greatest effect is on neural processing of
auditory stimuli
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No progress with auditory skill or inconsistent
skills
No benefit from HA’s
 Difficulty learning language by auditory
means alone
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Expressive and receptive S/L problems
 Strong visual learners
Developmental Profile of AN/AD
 Changes in abilities over time
 Wide variation in audiogram responses over
time
 Some infants with AN/AD have recovered
 Some children with ANAD have been
successful CI users
Audiometric findings
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PTA
SpRecognition
Tympanogram
OAEs
ABR:
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Cochlear microphonic –
Interventions
 Alternatives to auditory only input
 Visual input, Sign Language, Speech
Reading
 Ongoing ENT consult
 Cochlear Implant
 The VALUE of a REFERRAL
Useful websites on AN/AD
 www.kresgelab.org (see section on
information on deafness)
 Listserve for parents and patients:
www.auditoryneuropathy.com