Bilateral superior semicircular canal dehiscence - A rare cause of disequilibrium and pulsatile tinnitus
DOI:
https://doi.org/10.34631/sporl.78Keywords:
Superior semicircular canal dehiscence, autophonia, oscillopsia, dizziness, vestibular-evoked myogenic potentials, diagnosis, treatmentAbstract
Introduction: Superior semicircular canal dehiscence syndrome (SSCDS) is a recently recognized clinical condition which was initially described by Minor et al. in 1998. The proposed underlying mechanism involves the existence of a dehiscence of bone overlaying the superior semicircular canal creating a third mobile window which produces a path of least resistance that shunts acoustic energy through the vestibular labyrinth rather than through the cochlea. This syndrome may present with various symptoms such as sound or pressure induced vertigo (Tullio phenomenon) and oscillopsia along with hearing loss, autophony or tinnitus. It typically manifests as sound and/or pressure induced nystagmus at the plane of the SSC (vertical-torsional eye movements).
Subjects and methods: The authors report a case of bilateral superior semicircular canal dehiscence presenting with left pulsatile tinnitus and disequilibrium and demonstrate the clinical utility of vestibular-evoked myogenic potentials (VEMP) in the diagnosis of this unusual and underdiagnosed clinical entity.
Results: Diagnosis is based on the correlation of clinical symptoms, audiologic and vestibular testing and highresolution CT scan. Audiometric findings include low-frequency air-bone gap with preservation of acoustic reflexes. The most specific vestibular test available for SSCDS is VEMP testing. However, the established standard to confirm diagnosis is high-resolution temporal bone CT scan. Management of SSCDS is directed at symptom control and in many cases no treatment is required, besides reassurance and avoidance of the precipitating stimuli. Surgical repair is reserved for patients with disabling symptoms.
Conclusion: SSCDS is a rare disease and probably underdiagnosed. However, not all patients with a diagnosis of SSCDS will have classic symptoms and signs. A high index of suspicion with careful clinical examination and audiologic testing is required to identify these patients. VEMP testing can be very useful in diagnosing these patients.
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