title: Superior semicircular canal dehiscence simulating otosclerosis.
abstract: This is a report of a patient with an air-bone gap, thought 10 years ago to be a conductive hearing loss due to otosclerosis and treated with a stapedectomy. It now transpires that the patient actually had a conductive hearing gain due to superior semicircular canal dehiscence. In retrospect for as long as he could remember the patient had experienced cochlear hypersensitivity to bone-conducted sounds so that he could hear his own heart beat and joints move, as well as a tuning fork placed at his ankle. He also had vestibular hypersensitivity to air-conducted sounds with sound-induced eye movements (Tullio phenomenon), pressure-induced nystagmus and low-threshold, high-amplitude vestibular-evoked myogenic potentials. Furthermore some of his acoustic reflexes were preserved even after stapedectomy and two revisions. This case shows that if acoustic reflexes are preserved in a patient with an air-bone gap then the patient needs to be checked for sound- and pressure-induced nystagmus and needs to have vestibular-evoked myogenic potential testing. If there is sound- or pressure-induced nystagmus and if the vestibular-evoked myogenic potentials are also preserved, the problem is most likely in the floor of the middle fossa and not in the middle ear, and the patient needs a high-resolution spiral computed tomography (CT) of the temporal bones to show this.
authors.affiliation: Neurology Department, Royal Prince Alfred Hospital, Sydney, and the Otolaryngology Department, St Vincent's Hospital, Sydney, Australia. Michael@icn.usyd.edu.au
authors.forename: G Michael
authors.initials: GM
authors.lastname: Halmagyi
authors.forename: Swee T
authors.initials: ST
authors.lastname: Aw
authors.forename: Leigh A
authors.initials: LA
authors.lastname: McGarvie
authors.forename: Michael J
authors.initials: MJ
authors.lastname: Todd
authors.forename: Andrew
authors.initials: A
authors.lastname: Bradshaw
authors.forename: Robyn A
authors.initials: RA
authors.lastname: Yavor
authors.forename: Paul A
authors.initials: PA
authors.lastname: Fagan
mesh_terms: D000368:Aged; D001844:Bone Conduction / Q000502:physiology; D003937:Diagnosis, Differential; D005072:Evoked Potentials, Auditory; D006311:Hearing Disorders / Q000209:etiology* / Q000503:physiopathology; D006801:Humans; D007759:Labyrinth Diseases / Q000150:complications / Q000175:diagnosis* / Q000503:physiopathology; D008297:Male; D010040:Otosclerosis / Q000175:diagnosis* / Q000503:physiopathology; D012027:Reflex, Vestibulo-Ocular / Q000502:physiology; D012665:Semicircular Canals / Q000503:physiopathology; D013016:Sound; D036542:Tomography, Spiral Computed / Q000379:methods; D014724:Vestibular Function Tests; D014722:Vestibule, Labyrinth / Q000503:physiopathology