title: Superior-semicircular-canal dehiscence: effects of location, shape, and size on sound conduction.
abstract: The effects of a superior-semicircular-canal (SSC) dehiscence (SSCD) on hearing sensitivity via the air-conduction (AC) and bone-conduction (BC) pathways were investigated using a three-dimensional finite-element (FE) model of a human middle ear coupled to the inner ear. Dehiscences were modeled by removing a section of the outer bony wall of the SSC and applying a zero-pressure condition to the fluid surface thus exposed. At each frequency, the basilar-membrane velocity, vBM, was separately calculated for AC and BC stimulation, under both pre- and post-dehiscence conditions. Hearing loss was calculated as the difference in the maximum magnitudes of vBM between the pre- and post-dehiscence conditions representing a change in hearing threshold. In this study, BC excitations were simulated by applying rigid-body vibrations to the model along the directions of the (arbitrarily defined) x, y, and z axes of the model. Simulation results are consistent with previous clinical measurements on patients with an SSCD and with results from earlier lumped-element electrical-circuit modeling studies, with the dehiscence decreasing the hearing threshold (i.e., increasing vBM) by about 35 dB for BC excitation at low frequencies, while for AC excitation the dehiscence increases the hearing threshold (i.e., decreases vBM) by about 15 dB. A new finding from this study is that the initial width (defined as the width of the edge of the dehiscence where the flow of the fluid-motion wave from the oval window meets it for the first time) on the vestibular side of the dehiscence has more of an effect on vBM than the area of the dehiscence. Analyses of dehiscence effects using the FE model further predict that changing the direction of the BC excitation should have an effect on vBM, with vBM being about 20 dB lower due to BC excitation parallel to the longitudinal direction of the BM in the hook region (the x direction) as compared to excitations in other directions (y and z). BC excitation in the x direction and with a 'center' dehiscence located midway along the length of the SSC causes a reduction in the anti-symmetric component of the fluid pressure across the BM, as compared to the other directions of BC excitation, which results in a decrease in vBM at high frequencies. This article is part of a special issue entitled "MEMRO 2012".
authors.affiliation: Department of Mechanical Engineering, Stanford University, 496 Lomita Mall, Stanford, CA 94305, USA. kimnk@stanford.edu
authors.forename: Namkeun
authors.initials: N
authors.lastname: Kim
authors.forename: Charles R
authors.initials: CR
authors.lastname: Steele
authors.forename: Sunil
authors.initials: S
authors.lastname: Puria
mesh_terms: D000388:Air; D001844:Bone Conduction / Q000502:physiology*; D003051:Cochlea / Q000502:physiology; D003198:Computer Simulation; D004432:Ear, Middle / Q000502:physiology; D020342:Finite Element Analysis; D006309:Hearing; D034381:Hearing Loss; D006801:Humans; D008953:Models, Anatomic; D012665:Semicircular Canals / Q000502:physiology*; D013016:Sound; D055114:X-Ray Microtomography
references.citation: J Acoust Soc Am. 2006 Jul;120(1):258-69
references.pmid: 16875223
references.citation: J Acoust Soc Am. 2007 Nov;122(5):2738-58
references.pmid: 18189566
references.citation: Otol Neurotol. 2008 Oct;29(7):972-5
references.pmid: 18665008
references.citation: J Assoc Res Otolaryngol. 2011 Jun;12(3):261-79
references.pmid: 21360212
references.citation: Curr Opin Neurol. 2011 Feb;24(1):25-31
references.pmid: 21124219
references.citation: J Acoust Soc Am. 2010 Apr;127(4):2420-32
references.pmid: 20370025
references.citation: Hear Res. 2003 Jul;181(1-2):131-43
references.pmid: 12855371
references.citation: Otol Neurotol. 2004 May;25(3):323-32
references.pmid: 15129113
references.citation: Hear Res. 2010 May;263(1-2):85-92
references.pmid: 19900526
references.citation: Neurology. 2000 Dec 26;55(12):1833-41
references.pmid: 11134382
references.citation: Ann Biomed Eng. 2007 Dec;35(12):2180-95
references.pmid: 17882549
references.citation: Otol Neurotol. 2012 Jul;33(5):810-5
references.pmid: 22664896
references.citation: Biophys J. 2011 Jan 5;100(1):1-10
references.pmid: 21190651
references.citation: Am J Otol. 2000 Jan;21(1):9-19
references.pmid: 10651428
references.citation: Otolaryngol Head Neck Surg. 2011 Oct;145(4):648-53
references.pmid: 21602535
references.citation: Hear Res. 2004 Jan;187(1-2):105-10
references.pmid: 14698091
references.citation: Hear Res. 2001 Feb;152(1-2):100-9
references.pmid: 11223285
references.citation: Hear Res. 2005 Dec;210(1-2):53-62
references.pmid: 16150562
references.citation: Hear Res. 2010 Oct 1;269(1-2):70-80
references.pmid: 20638462
references.citation: J Acoust Soc Am. 2007 Aug;122(2):943-51
references.pmid: 17672643
references.citation: Arch Otolaryngol Head Neck Surg. 1998 Mar;124(3):249-58
references.pmid: 9525507
references.citation: Acta Otolaryngol. 1978 Sep-Oct;86(3-4):225-32
references.pmid: 707065
references.citation: Nat Neurosci. 2005 Feb;8(2):132-4
references.pmid: 15682184
references.citation: Otol Neurotol. 2004 Mar;25(2):121-9
references.pmid: 15021770