Transcript DDx Cont.
Pseudo-conductive Hearing Losses Bastaninejad, Shahin, MD, Assistant Professor of ORL, TUMS, Amir’Alam Hospital Definition of Pseudo-conductive Hearing Loss Apparent conductive hearing loss on audiometric testing, that is not due to pathology in the external or middle ear Case Presentation • 10yr old boy • CHL in Left ear, found during a routine school-hearing test • Left side Rinne’s test was negative • AR in Left ear: Ipsi.neg., Contra.Pos. • CTnl. • No history of trauma and… Hamad Al Muhaimeed, et al. Conductive hearing loss: investigation of possible inner ear origin in three cases studies. The Journal of Laryngology & Otology November 2002, Vol. 116, pp. 942–945 Case Cont. • The provisional diagnosis was ossicular disruption medial to the neck of the stapes (to explain the presence of the contralateral stapedial refl• ex) • Exploration performed all ossiceles were mobile, FP was mobile, but Round window reflex was negative Importance Some causes of these pseudo-conductive hearing losses can be diagnosed without resorting to surgery Bibliography • The concept of inner ear conductive hearing loss was proposed as early as the 1960s by Gloris and Davis and by Nixon and Glorig. They proposed stiffness of the cochlear partition as a possible cause Proposed Mechanisms for a True Pseudo-CHL • Third window effect • lesions in the: – Scala vestibuli – Helicotrema – Scala tympani – Basilar membrane Transmission Problem Inner ear conductive hearing loss • Obliterated round window membrane Normal Cochlear Transmissions key discriminating features • Presence of AR in the ear with CHL – Exception: crossed or may be a normal stapedial reflexes can be present if there is fracture in the stapes crura or footplate medial to the insertion of the stapedius tendon key discriminating features • Round window reflex findings: – Presence When Otosclerosis is suspected – Absence In the presence of an obviously mobile footplate Other differentiating features Sup.SCC Dehiscence - Audiogram Differential Diagnosis • Poor Masking and Poor Audiometry: – Perhaps the most common cause of pseudoconductive hearing loss is the presence of a unilateral or asymmetric sensorineural hearing loss in which the better hearing inner ear is poorly masked perform tuning fork test in all subjects – Collapsing ear canals DDx Cont. • Functional Hearing Loss: – Must be considered in any patient with an unusual conductive hearing loss pattern: • Some subjects who are exaggerating their hearing loss have difficulty estimating the loudness level of the two different stimuli different CHL in two consecutive assessments… • Also they may have an inverse air–bone gap! DDx Cont. • Third Window can arise from a fistula into the cochlea or the labyrinthine portion of the inner ear – Semicircular Canal Dehiscencies (Superior, Inferior and Lateral) – LVA – X-Linked Deafness With Stapes Gusher – Dehiscence Between the Cochlea and Carotid Canal – Paget Disease of the Temporal Bone – Some inner Ear Malformations Saumil N. Merchant and John J. Rosowski. Conductive Hearing Loss Caused by Third-Window Lesions of the Inner Ear. Otol Neurotol. 2008 April ; 29(3): 282–289 DDx Cont. • Round Window Obliteration • Inner Ear Mechanical Conductive Loss – One of the types of presbycusis (CHL with Mixed loss at 4k and 8k) – Changes in BM pliability – Lesions in the scala vestibuli, helicotrema and scala tympani – Co-existed with some forms of the congenital hearing losses DDx Cont. • Missed Middle Ear Pathology – Otosclerosis with a flexible suprastructure – Malleus or incus fixation or stiffness – Pathology at the lenticular process of the incus – Floppy tympanic membrane – Adhesions lysed during the approach for exploration – Transient pathology at the time of audiogram Conclusion Think about plausibility of Pseudo- conductive hearing loss and include it’s possibility in your pre-operative evaluation and patient consent before proceeding to the middle ear exploration