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Superior semicircular canal dehiscence simulating otosclerosis.
G Michael Halmagyi1, Swee T Aw, Leigh A McGarvie
1Neurology Department, Royal Prince Alfred Hospital, Sydney, and the Otolaryngology Department, St Vincent's Hospital, Sydney, Australia. Michael@icn.usyd.edu.au
The Journal of Laryngology and Otology
|August 7, 2003
Summary
Misdiagnosed otosclerosis may actually be superior semicircular canal dehiscence. Preserved acoustic reflexes in air-bone gap patients warrant testing for nystagmus and vestibular-evoked myogenic potentials.
Area of Science:
- Otolaryngology
- Neurotology
- Audiology
Background:
- A patient presented with an air-bone gap initially diagnosed as otosclerosis and treated with stapedectomy.
- The patient exhibited symptoms suggestive of a conductive hearing gain rather than loss.
Observation:
- The patient reported hypersensitivity to bone-conducted sounds (cochlear) and air-conducted sounds (vestibular).
- Symptoms included sound-induced eye movements (Tullio phenomenon), pressure-induced nystagmus, and preserved acoustic reflexes post-surgery.
- Low-threshold, high-amplitude vestibular-evoked myogenic potentials were noted.
Findings:
- The patient's condition was re-evaluated and identified as superior semicircular canal dehiscence.
- Preserved acoustic reflexes in the presence of an air-bone gap are a key diagnostic indicator.
Implications:
- This case highlights the importance of considering superior semicircular canal dehiscence in patients with unexplained air-bone gaps and preserved acoustic reflexes.
- Recommended diagnostic steps include testing for nystagmus and vestibular-evoked myogenic potentials.
- High-resolution computed tomography (CT) of the temporal bones is crucial for confirming dehiscence in the middle fossa floor.