Transcript INNER EAR CONDUCTIVE HEARING LOSS

INNER EAR CONDUCTIVE
HEARING LOSS
Prof. Hamad Al Muhaimeed
Prof. Yousry El Sayed
Dr. Abdulrahman Rabah
Dr. Abdulrahman Essa
Department of ORL
King Abdul Aziz University
Riyadh, Saudi Arabia
Inner Ear Conductive HL
Cochlea prefers 2 functions:
1) Transmission of sound energy
= oval window to basilar membrane
2) Transduction of the mechanical (acoustic)
energy) --> electrical (neural energy)
= organ of corti
Inner Ear Conductive HL
• Lesion of hair cells --> SNHL
• Lesions in scala vestibuli, helicotrema,
scala tympani, or basilar membrane
--> CHL
– Inner ear CHL will be characterized
by absent RWR + normal contralateral stapedial reflex
Inner Ear Conductive HL
Case 1:
– 10 year old boy
– Lt. hearing loss
– No history of trauma, infections,
-ve family history of HL
– Otoscopy: NAD
– Tuning fork test: +ve Rt.; -ve Lt.
= Weber --> Lt.
Inner Ear Conductive HL
Case 1: (cont.)
– PTA
– Tympanometry: Ipsilateral stapedial
reflex absence Lt., present Rt.
> Contralateral - St. reflex was
elicited in Lt.
– C.T. scan Temporal bone: Normal
cochlea, cochlear aqueduct, no signs
of cholesteatoma
Inner Ear Conductive HL
Case 1: (cont.)
– Provisional diagnosis: Ossicular
disruption medial to neck of the
stapedius
– Lt. tympanotomy:
• intact & mobile ossicles
• normal footplate movement
• RW reflex -ve
– ABR: conductive nature of HL
Inner Ear Conductive HL
Case 2:
– 20 year old girl
– Progressive Lt. HL for 5 years
– No hx of ear discharge, tinnitus,
vertigo or trauma
– Otoscopy: NAD
– Tuning fork test: Consistent with Lt. CHL
– PTA
– Tympanometry: Contralateral St. reflex
was elicited in Lt.
Inner Ear Conductive HL
Case 2: (cont.)
– C.T. scan : NAD
– Lt. tympanotomy: NAD + -ve RWR
– ABR: Hearing threshold is 80 dBHL
with shifting of wave latency
Inner Ear Conductive HL
Case 3:
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38 year old man
Bil. HL with tinnitus for 2 years
No hx of ear discharge, vertigo or trauma
Otoscopy: NAD
Rinne: -ve bilaterally
Weber test is central
PTA
Tympanometry
Rt. Tympanotomy: NAD + -ve RWR
CT scan: NAD
Inner Ear Conductive HL
History
The concept of inner ear CHL has been
proposed as early as 1960s by Gloris &
Davis, Nixon & Glorig (stiffness of the
cochlear partition.
Shea: Inner ear CHL occurs in 1:700
pts. with otosclerosis.
Inner Ear Conductive HL
Discussion
– Lesion of the external & middle ear
affecting the sound conduction or/and
the transformer functions --> CHL
– Lesions affecting hair cells
[transduction] --> SNHL
– Lesions affecting scala vestibuli,
helicotrema, scala tympani, or basillar
membrane (sound conduction)--> CHL
Inner Ear Conductive HL
Discussion (cont.)
You should exclude:
– Inorganic deafness
– SNHL with shadow bone conduction
Diagnosis of CHL in the 3 cases has
been confirmed by:
1)
2)
3)
4)
Repeated tuning fork test
PTA with masking
ABR
Stapedial reflex
Inner Ear Conductive HL
Discussion: (cont.)
Surgical exploration had excluded any
middle ear abnormalities including
congenital cholesteatoma.
Consequently, CHL is most likely due
to an anatomic or functional lesion in
the cochlea proximal to the sensory
part (hair cells).
Inner Ear Conductive HL
Discussion (cont.)
Possible causes of inner ear CHL:
1) Abnormal perilymp pressure
- Cremers et al, 1983
2) Stiffness of the basilar membrane
- Nodal, 1979
This is more reasonable to cause
HL in 3 cases.
Inner Ear Conductive HL
Causes:
– The 1st case is probably due to congenital
cause since birth while the others may
be acquired.
– The elevated bone conduction threshold
seen in some frequencies may be interpreted as mixed HL secondary to affection
of the hair cells by the same aetiological
agent.
Inner Ear Conductive HL
Discussion (cont.)
Bone conduction threshold is NOT
just a measure of hair cell function.
Some disorders may falsely enhance
the bone conduction while others may
falsely decrease it e.g. Carhart effect.
- Dirks, 1985
Inner Ear Conductive HL
Discussion: (cont.)
– Diagnosis & treatment of CHL due to
external or middle ear abnormalities
are well documented. It includes
clinical, audiological, radiological
examinations.
– Diagnosis of inner ear CHL is a
difficult task.
Inner Ear Conductive HL
Causes:
The 1st two young pts. showed unilateral HL
while the 3rd case (38 yr) showed bil. HL
– Is the main lying pathology in all
cases the same?
– Is this pathology progressive that
involved the other side as the age
advances?
Inner Ear Conductive HL
Discussion: (cont.)
The anatomic correlate to inner ear
CHL is not completely understood.
Probably the functional loss is due to
impairment of the vibration of the
basillar membrane as a result of
abnormality in the scala vestibuli,
helicotrema, & scala tympani or
basillar membrane.
Inner Ear Conductive HL
Discussion (cont.)
Positive contralateral stapedial reflex:
1) Fractured crurae of the stapedes
2) Ossicular disruption with presence
of soft tissue connection between
stapes and incus.
Inner Ear Conductive HL
Conclusion:
Three cases of mainly CHL thought to be due
to derangements of the sound conduction
function of the inner ear.
The pathophysiology is not clear due to
inaccessibility of the cochlea for clinical
examination and lack of histopathological
studies. More studies are needed to clarify
this matter.
These pts. need to be followed to see the
progress of inner ear pathologies.