HHI
Hereditary hearing impairment
> 50% of childhood hearing impairment
2/3 are nonsyndromic (>110 loci harboring genes)
70-80% of the nonsyndromic is Auto Rec (usu congenital and profound)
15-20% of the nonsyndromic is Auto Dom (usu adolescence/adults and varied severity)
Impedence-matching
The structures of the middle ear serve as an impedence-matching mechanism improving the efficiency of energy transfer fromt he air to the fluid-filled inner ear
Pathway of sound starting at CN 8
SLIM 41) CN8, spiral ganglion, cochlear nucleus, superior olivary nucleus, lateral leminiscus, nucleus of lateral lemniscus, lateral leminiscus, inferior colliculus, brachium of inferior colliculus, medial geniculate ganglion, broadman’s area 41/ sup trans gyrus of Heshl
How is intensity of sound encoded?
- The amount of neural activity in individual neurons
- Number of neurons that are active
- The specific neurons that are activated
GJB2
Gene that encodes connexin 26
20% of childhood deafness
Variable severity but usu severe to profound at birth
50% can be screened by just 2 frameshift mutations: 35delG and 167delT
Presbycusis
MCC hearing loss in adults
Significant loss in clarity
Has environmental and genetic component (GRM7 gene)
Loss of discrimination for phonemes, recruitment (abnl growth of loudness), & particular difficulty understanding speech in noisy environment
Syndromic SNHL
Over 200 syndromes
- Usher synd (RP and SNHL)
- Waardenburg synd (pigmentary abnlity and SNHL)
- Pendred synd (thyroid organification defect and SNHL)
- Alport synd (renal dz and SNHL)
- Jervell and Lange-Nielsen synd’s (prolonged QT and SNHL)
Goals of evaluating a pt w/ hearing complaint
- The nature of the hearing impairment (CHL vs SNHL)
- The severity (mild, mod, severe, profound)
- The anatomy (ext ear, mid ear, inner ear, central auditory pathway)
- The etiology
History for hearing loss
Duration of deafness
Nature of onset (sudden or insidious)
Rate of progression (rapid or slow)
U/l vs b/l
Assoc Sx: tinnitus, vertigo, imbalance, aural fulness, hyperacusis, otorrhea, HA, CN 7 dysfnc, H&N paresthesia
H/o head trauma, ototoxic exposure, noise exposure (occupational or recreational)
Family Hx hearing loss
What amount of hearing loss is required for an abnormal Rinne test?
30 dB or greater CHL
What amount of hearing difference between the two ears is required for a lateralizing Weber?
5 dB
What is the minimum audiologic assessment for hearing loss?
- Pure-tone AC and BC thresholds
- Speech reception threshold
- Discrimination score
- Tympanometry
- Acoustic reflexes
- Acoustic-reflex decay
This allows the determination of whether further differentiation of a sensory (cochlear) from a neural (retrocochlear) hearing loss is indicated
What imaging studies should be ordered for hearing loss?
Most pts w/ CHL should get axial and direct coronal CT scans of T bones to evaluate external and middle ear
Pts w/ u/l SNHL should get MRI w/ gad to exclude CPA tumors
In presence of vestibular Sx, pt may need electronystagmography and caloric testing
CT imaging for hearing loss
Axial and coronal of T bone w/ fine 0.6mm cuts
- Determine caliber of EAC
- Integrity of ossicular chain
- Presence/absence of middle ear or mastoid dz
- Detecting inner ear malformations (must measure cochlear height, LSCC bony island width, and vestibular aqueduct)
- Detecting bone erosion (e.g. chronic otitis media, cholesteatoma)
MRI for hearing loss
Superior for imaging retrocochlear pathology (vestibular schwannomas, meningiomas, other lesions of CPA)
Tx of SNHL
- Creating a favorable environment for hearing (eliminate/reduce unnecessary noise to enhance signal-to-noise ratio; lip reading; appropriate rate of speech)
- Amplification
- Cochlear implants
- Brainstem auditory implants
