Superior semicircular canal dehiscence: a narrative review

Abstract

Background Described just over 20 years ago, superior semicircular canal dehiscence remains a relatively unknown and easily missed cause of dizziness and auditory symptoms. Objective This review focused on the origin, presenting symptoms and underlying pathophysiology of superior semicircular canal dehiscence, and the available treatment options. Main findings and conclusion The bony dehiscence acts as a ‘third window’, affecting inner-ear homeostasis, and resulting in hypersensitivity and a vestibular response to lower sound level stimuli. The third window effect explains the pressure- and sound-induced vertigo, oscillopsia, and nystagmus, as well as autophony, conductive hyperacusis and tinnitus. The origin of superior semicircular canal dehiscence is linked to the combination of a congenital or developmental factor, and a ‘second event’ like head trauma, rapid pressure changes or age-related factors. Computed tomography of the temporal bone and reduced vestibular-evoked myogenic potential thresholds can confirm the diagnosis. Despite only retrospective cohorts, surgery is considered a safe treatment option, targeting mainly vestibular but also auditory symptoms, with transmastoid approaches gaining popularity.

Scuba Diving-Induced Inner-Ear Pathology: Imaging Findings of Superior Semicircular Canal and Tegmen Tympani Dehiscence

“…Although the exact etiology of SSCD is unclear, it is thought that both primary and secondary factors are involved. The presence of a thin segment of bone overlying the superior semicircular canal is a strong predisposing factor for SSCD following a trauma to the head or increased inner-ear pressure [ 2 , 10 – 12 , 15 , 16 ].…”

“…Superior semicircular canal dehiscence (SSCD) is characterized by loss of the bone overlying the superior semicircular canal of the inner ear and was first described by Minor and colleagues in 1998 [ 1 ]. Patients presenting with SSCD often experience hearing loss, disequilibrium, autophony, oscillopsia, and noise-induced vertigo [ 1 , 2 ]. Cadaveric studies have shown that SSCD has an approximate incidence of 0.7% [ 3 ], while radiological studies have reported an incidence rate of 3–9%, making SSCD a relatively rare disorder [ 4 , 5 ].…”

“…Briefly, dehiscence of the segment of temporal bone, located above the superior semicircular canal, creates a ‘third window,’ which increases inner-ear immittance and perturbs normal endolymph dynamics, particularly when exposed to high-level sounds or pressure changes [ 8 – 11 ]. Hence, patients with suspected SSCD will typically show an air-bone gap (conductive hearing loss) and rotational nystagmus induced by pressure changes (Henebert’s sign) or sound (Tullio phenomenon) upon examination [ 2 , 10 – 12 ].…”

An evidenced-based diagnostic tool for superior semicircular canal dehiscence syndrome

“…Superior semicircular canal dehiscence (SSCD) is caused by a thinning or absence of the bone overlying the superior semicircular canal ( Minor et al., 1998 ; Kontorinis and Lenarz, 2022 ). The area of dehiscence is believed to cause a “third window” which results in a loss in the conduction of mechanical energy through the labyrinth upon sound and pressure stimulation ( Kontorinis and Lenarz, 2022 ). Initially described by Minor et al.…”

“…Initially described by Minor et al. (1998) , SSCD can lead to a variety of otologic and vestibular symptoms including disequilibrium, autophony, hyperacusis, aural fullness, hearing loss, tinnitus, and vertigo ( Kontorinis and Lenarz, 2022 ; Naert et al., 2018 ).…”