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 contra- lateral 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: – 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) Repeated tuning fork test 2) PTA with masking 3) ABR 4) 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, ) 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 inter- preted 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.