Relationship Between Clinical Features and the Arc and Length of Dehiscence in SCDS: A Single Center Review of 42 Cases

Narrowing of Low-Frequency Air-Bone Gap and Its Association with Symptom Resolution Following Superior Canal Dehiscence Repair

OBJECTIVE

Low-frequency air-bone gap (LABG) on pure tone audiometry is an expected clinical finding of superior canal dehiscence (SCD) syndrome. We investigate how narrowing of LABG following SCD repairs translates to symptom resolution.

STUDY DESIGN

Cohort study.

SETTING

Tertiary Care Center.

METHODS

We analyzed consecutive SCD repairs at an institution between 2012 and 2022. Pure tone audiometry and symptom questionnaires were administered pre- and post-operatively. The independent variable assessed whether the LABG narrowed (≥5 dB) following surgery. Outcome measures were rates of Overall Symptom Improvement (OSI, net resolution of ≥1 symptom) and Symptom Resolution Score (SRS, % symptoms resolved). We conducted multivariable regression analyses with LABG narrowing as the primary predictor. All models controlled for demographics, bilateral disease, prior ear surgery, and follow-up.

RESULTS

Among total of 217 repairs analyzed, 161 (74%) reached OSI, and mean SRS was 39 (out of 100). LABG narrowing at 250 Hz (65%), 500 Hz (52%), and 1000 Hz (47%) was associated with a 41-point (β 95% confidence interval [CI] 5-77) increase in auditory, 15-point (β 95% CI 1-30) increase in auditory, and 23-point (β 95% CI 2-45) increase in vestibular SRS, respectively. However, LABG narrowing was not significantly associated with the rates of auditory and vestibular OSI at all frequencies assessed.

CONCLUSION

Lack of LABG narrowing following repair was associated with the persistence of a greater proportion of preoperative symptoms but similar likelihood of OSI. This relationship was more prominent for auditory symptoms at 250 to 500 Hz and for vestibular symptoms at 1000 Hz. Additional research is warranted to elucidate the mechanism through which symptoms resolve despite LABG persistence.

Impaired Vestibulo-Ocular Reflex on Video Head Impulse Test in Superior Canal Dehiscence: "Spontaneous Plugging" or Endolymphatic Flow Dissipation?

Surgical plugging of the superior semicircular canal (SSC) represents an effective procedure to treat disabling symptoms in superior canal dehiscence (SCD), despite resulting in an impaired vestibulo-ocular reflex (VOR) gain for the SSC. On the other hand, SSC hypofunction on video head impulse test (vHIT) represents a common finding in patients with SCD exhibiting sound/pressure-induced vertigo, a low-frequency air-bone gap (ABG), and enhanced vestibular-evoked myogenic potentials (VEMPs). "Spontaneous canal plugging" has been assumed as the underlying process. Nevertheless, missing/mitigated symptoms and/or near-normal instrumental findings would be expected. An endolymphatic flow dissipation has been recently proposed as an alternative pathomechanism for SSC VOR gain reduction in SCD. We aimed to shed light on this debate by comparing instrumental findings from 46 ears of 44 patients with SCD exhibiting SSC hypofunction with post-operative data from 10 ears of 10 patients with SCD who underwent surgical plugging. While no difference in SSC VOR gain values was found between the two groups (p = 0.199), operated ears developed a posterior canal hypofunction (p = 0.002). Moreover, both ABG values (p = 0.012) and cervical/ocular VEMP amplitudes (p < 0.001) were significantly higher and VEMP thresholds were significantly lower (p < 0.001) in ears with SCD compared to operated ears. According to our data, canal VOR gain reduction in SCD should be considered as an additional sign of a third window mechanism, likely due to an endolymphatic flow dissipation.

Computed tomography approximated superior semicircular canal dehiscence size and location and their association with clinical presentation

OBJECTIVE

This study investigates the relationship of superior semicircular canal dehiscence (SSCD) size and location with patient symptomatology and audiometry.

METHODS

We retrospectively reviewed SSCD cases presented to a tertiary institution between 2011 and 2022. Dehiscence length and width measured on high-resolution temporal bone computed tomography imaging were used to calculate an approximate dehiscence area (ADA). Dehiscence location was classified employing a six-grade system. Multivariable regression analyses were performed with symptomatology and audiogram metrics as outcome variables and ADA and dehiscence location as the primary covariates of interest.

RESULTS

A total of 402 SSCD were included in the analysis. Controlling for patient age, sex, dehiscence laterality, and location, greater ADA was independently associated higher rates of autophony (aOR 1.39; 95% C.I. 1.14-1.71; P = 0.004) and hyper-amplification (aOR 1.39; 1.14-1.70; P = 0.004). Additionally, dehiscences with greater ADA exhibited significantly lower bone conduction threshold at 500 Hz (adjusted β -1.75, P = 0.006) and 1000 Hz (adjusted β -1.61, P = 0.018) and significantly wider air-bone gap at 500 Hz (adjusted β 2.22, P < 0.001) and 1000 Hz (adjusted β 1.00, P = 0.039). Dehiscence location was not independently associated with any outcome variable examined when accounting for dehiscence size.

CONCLUSION

The size of dehiscence is more independently related to clinical presentations than the anatomical location of the dehiscence in the superior semicircular canal. Greater dehiscence size is associated with symptomatology and audiometry consistent with more severe bone conduction hyperacusis.