Auditory outcomes after labyrinthine surgery for superior semicircular canal dehiscence repair and posterior canal occlusion

Introduction

Superior semicircular canal dehiscence (SSCD) and benign paroxysmal positional vertigo (BPPV) are pathologies originating from within the semicircular canals, and although not life threatening, these diseases can be extremely debilitating and impair quality of life. For patients with mild symptoms, avoidance of stimuli and repositioning manoeuvres are offered as first line treatments for SSCD and BPPV respectively. Surgical management is offered to patients with SSCD experiencing symptomatic balance disturbance or debilitating auditory symptoms, or BPPV that is refractory to conservative treatment. Hearing loss is a potential risk in all otological surgeries which must be communicated to patients prior to surgery (1). Surgeries involving the semicircular canals have been associated with a risk of sensorineural hearing loss (SNHL) (2-4). As SSCD and BPPV originate in the inner ear, invasive procedures used to treat these conditions may lead to SNHL. In this case series we compare auditory outcomes between patients who underwent SSCD repair or posterior canal occlusion (PCO) for BPPV, with a focus on bone conduction pure tone average (BC PTA) as a direct measure for sensorineural hearing. This study aims to examine the sensorineural hearing outcomes after SSCD repair and PCO to facilitate improved pre-operative counselling of hearing risks to patients undergoing these procedures.

SSCD

SSCD is a rare condition characterised by a defect within the bony exterior of the semicircular canal resulting in the formation of a third window within the superior canal (5,6). First described in the late 1990s as a syndrome of vertigo and oscillopsia by Minor et al. (6,7), it was hypothesised that the presence of the third window lowered the total impedance of the inner ear, resulting in brief episodes of vertigo and nystagmus during periods of increased intracranial pressure or loud sounds. Symptoms of hyperacusis, autophony and pulsatile tinnitus are also experienced by patients.

Surgical management of the affected canal typically involved plugging, capping, or resurfacing of the defect in the superior semicircular canal, accessed via a middle cranial fossa (MCF) or transmastoid (TM) approach (5).

A major advantage of the MCF approach is the ability to directly visualise the dehiscence, allowing for repair via plugging using bone pate, fascia or wax, resurfacing using bone graft or capping with hydroxyapatite cement (8). Given the approach’s invasive nature, it has been associated with a risk of cerebrospinal fluid leak, SNHL, facial paralysis, seizures and intracerebral haemorrhage (9).

The TM approach involves a standard mastoidectomy to provide visualisation of the superior semicircular canal (10). An advantage of the TM approach is that it avoids an intracranial procedure and the attendant risks as described previously; however, it requires repair of the dehiscence to be performed indirectly and without direct visualisation of the defect. Both plugging and modified resurfacing techniques have been used with this approach (10).

BPPV

BPPV is a disorder characterised by short episodes of vertigo triggered by specific of head movements. It is thought to be caused by canalithiasis, displaced otoliths within the anterior, horizontal or posterior semicircular canals, with posterior canal BPPV being the most common (11,12). The debris disrupts the movement of endolymph within the canal during head movements involving linear accelerations. This results in a transient sensation of spinning that typically last from seconds to minutes. Episodes of nausea and vomiting and imbalance are also reported. Hearing loss and other auditory symptoms are typically absent (12).

BPPV is effectively treated using particle repositioning manoeuvres, including the Epley manoeuvre and Semont manoeuvre, which encourage the otoliths to move towards the common crus of the anterior and posterior semicircular canals and exit into the utricle, providing instant symptom relief (13-15). Patients with BPPV refractory to repositioning manoeuvres are offered surgical treatment as a last resort including PCO.

PCO was first introduced in the 1990s by Parnes and McClure (16,17), to treat intractable BPPV via the TM approach. The goal of the procedure was to prevent endolymph flow within the semicircular canals through extraluminal occlusion of the posterior semicircular canal (17). This would render the cupula unresponsive to angular accelerations, and importantly canalithiasis, relieving the patient from vertigo.

Methods

Ethical approval

The study was conducted in accordance with the Declaration of Helsinki and its subsequent amendments. The study was approved by the Ramsay Health Care HREC (HREC Reference 2025/ETH/0041). The requirement for individual consent was waived as this was a low-risk retrospective review. The study is reported according to the STROCSS reporting guidelines (available at https://www.theajo.com/article/view/10.21037/ajo-25-23/rc).

Inclusion criteria

A retrospective case review was conducted of all adult subjects who underwent SSCD repair or PCO at a tertiary referral centre between 2009 and 2024. Patients were included if they were adults and had pre- and post-operative audiograms

Surgical technique

Surgical approach was determined on an individual basis. In general, patients with isolated superior canal dehiscence and a well pneumatised mastoid were offered a TM procedure. Those with associated tegmen defects (with or without encephalocoeles) or sclerotic mastoids were managed via a MCF approach. All surgeries were performed by the senior author.

MCF approach to SSCD

MCF plugging was carried out via a middle fossa craniotomy. Extradural elevation of the temporal lobe was performed to expose the entire tegmen mastoideum and tympani. The dehiscent focus in the superior semicircular canal was identified, and the canal was occluded with temporalis fascia or bone wax. The entire tegmen was resurfaced with hydroset cement (Stryker Co., Limerick, Ireland). Meticulous haemostasis was achieved prior to closure; the bone flap was secured with mini-plates or cement and the wound was closed in layers.

TM occlusion of superior semicircular canal

The procedure was performed via a post-auricular approach. A cortical mastoidectomy was followed by identification of the facial nerve and all three semicircular canals. The superior canal was skeletonised and blue-lined on its internal surface. The canal was opened with 45- and 90-degree picks, being careful to preserve the membranous canal. The canal was then occluded with temporalis fascia on either side of the fenestration. The bony defect was repaired with bone wax or hydroset cement and the wound was closed in layers.

TM occlusion of the posterior semicircular canal

The procedure was performed via a post-auricular approach. A cortical mastoidectomy was followed by identification of the facial nerve and the lateral and posterior semicircular canals. The posterior canal was skeletonised and blue-lined with a 1-mm diamond burr, at or below the level of the lateral canal (Donaldson’s line) to avoid damage to the crus commune. The canal was opened with 45- and 90-degree picks, being careful to preserve the membranous canal. The canal was then occluded with temporalis fascia on either side of the fenestration. The bony defect was repaired with bone wax or hydroset cement and the wound was closed in layers.

Audiometric data

Each subject had at least one pre-operative and post-operative audiogram. In patients with multiple post-operative audiograms, the latest audiogram was used. Bone conduction (BC) at 250, 500, 1,000, 2,000 and 4,000 Hz were used to calculate PTA for the affected ear.

Primary outcome measures and subgroup analysis

Primary outcome measures include BC PTA for the affected ear. Change in BC PTA between pre- and post-operative audiograms were calculated for a pooled sample, and for each surgical approach (SSCD, MCF, TM, PCO).

Data analysis

Microsoft Excel and Jamovi (version 2.6.44) were used to collect audiometric data and perform statistical analysis. As the data was not normally distributed, a Wilcoxon signed-rank test was used to compare medians from pre- and post-operative audiometric data. Nonparametric confidence intervals (CIs) of 95% were reported around a point estimate of the median of the difference between pre-operative and post-operative audiograms and were based on normal approximations (18). Statistical significance was considered using a two-tailed P value of <0.05 (19). Test statistic is represented by W. Effect size was calculated using rank biserial correlation (r_rb) (20).

Results

Thirty-two operations on 30 subjects were analysed. This included 22 ears in the MCF subgroup, 5 ears in the TM subgroup, and 5 ears in the PCO subgroup. One revision case was performed for SSCD, with the patient having a TM repair before an MCF procedure. Bilateral procedures were performed in one patient for SSCD. The mean age was 54.5±12.6 years (range, 34–80 years). The TM group was the youngest at 44.4±5.1 years, with the MCF group at 55.9±11.7 years and PCO group at 58.6±18.2 years. Overall, labyrinthine surgery was performed on 14 males (44%) and 18 females (56%), with 14 procedures performed on right ears (44%) and 18 (56%) on left ears. The MCF group comprised 8 males (36%) and 14 females (64%) with procedures performed on 8 right ears (36%) and 14 left ears (64%). The TM group comprised 3 males (37.5%) and 2 females (62.5%) with procedures performed on 1 right ear (20%) and 4 left ears (80%). The PCO group comprised 3 males (60%) and 2 females (40%) with procedures all performed on right ears (100%). The average length of audiometric follow-up was 2.8±2.0 months. Baseline demographics are displayed below in Table 1.

Table 2 shows pre- and post-operative audiometric data in a pooled sample, as well as subgroup analysis for surgical approach.

The point estimate for the median of the difference in BC PTA between pre- and post-operative audiograms with 95% CIs, statistical significance calculations and effect sizes are presented in Table 3. A positive ΔBC PTA indicates a SNHL.

In a pooled analysis, there was a statistically significant worsening BC PTA from a median of 15.0 dB pre-operatively to 17.0 dB post-operatively, with a point estimate for the median of the difference of 3.5 dB (95% CI: 0.5, 6.5, W=365.5, P=0.022, r_rb=−0.47). Procedures performed to treat SSCD had a worsening BC PTA from a median of 15.0 dB pre-operatively to 16.0 dB post-operatively, with a point estimate of 4.0 dB (95% CI: 1.0, 7.5, W=278, P=0.009, r_rb=−0.58). The MCF approach was associated with a worsening BC PTA from a median of 16.0 pre-operatively to a median of 16.5 post-operatively, with a point estimate of 4.0 dB (95% CI: 1.0, 9.5, W=180.5, P=0.025, r_rb=−0.56). There was no statistically significant change in BC PTA after the TM approach, with a median of 10.0 dB pre-operatively to 13.0 dB post-operatively (4.5 dB, 95% CI: −3, 8, W=13, P=0.188, r_rb=−0.73). In the PCO group, there was no statistically significant change in BC PTA from a median of 18 dB pre-operatively to 22 dB post-operatively (−1 dB, 95% CI: −12, 10, W=7, P=1.0, r_rb=0.07).

Changes in BC PTA were partitioned into the following dB ranges: ≤10, 11–20, 21–40, >40 dB. Figure 1 shows the number of patients in each range and further divide them into each surgical subgroup.

Figure 1 Change in BC PTA divided into threshold ranges and subgroups. BC PTA, bone conduction pure tone average; dB, decibels; MCF, middle cranial fossa; PCO, posterior canal occlusion; SSCD, superior semicircular canal dehiscence; TM, transmastoid.

Twenty-three of the 32 cases reported a worsening in BC PTA. There were 19 cases of <10 dB ΔBC PTA (13 MCF, 4 TM, 2 PCO), 1 case of 11–20 dB ΔBC PTA (MCF) and 3 cases of 21–40 dB ΔBC PTA (all MCF).

Discussion

SSCD repair and PCO are surgeries offered to patients with SSCD experiencing debilitating auditory symptoms or balance disturbance and intractable BPPV respectively. In the current literature, there is conflicting evidence on the hearing outcomes after these procedures.

Our study found a statistically significant worsening BC PTA of 3.5 dB (95% CI: 0.5, 6.5, W=365.5, P=0.022, r_rb=−0.47) in a pooled sample, 4.0 dB (95% CI: 1.0, 7.5, W=278, P=0.009, r_rb=−0.58) in procedures used to treat SSCD, and 4.0 dB (95% CI: 1.0, 9.5, W=180.5, P=0.025, r_rb=−0.56) after the MCF approach. It is hypothesised that the presence of a third window in SSCD artificially enhances bone conduction thresholds as it results in an increased inequality in impedance between the scala tympani and scala vestibuli, causing sound to be shunted through the third window (21,22). After SSCD repair, bone conduction thresholds increase as intra-labyrinthine impedance increases, which is supported by our findings. Similar auditory findings are reported by Lin et al. who explored auditory outcomes after SSCD plugging via MCF and TM approach, and PCO (23). They reported a statistically significant worsening in BC PTA of <5 dB in a pooled sample of 87 cases, and in MCF and TM subgroups. This is supported by Ward et al. who investigated the hearing outcomes of 43 patients undergoing SSCD plugging via the MCF approach (24). The study reported a persistent mild SNHL of <10 dB post-operatively in 25% of patients at 3–15 months postoperatively. In contrast, Ellspermen et al. conducted a relatively large study on 50 ears, with 24 ears in the MCF group and 26 ears in the TM group, and found no statistically significant change in BC PTA (9). Surgeries were performed by one of four surgeons, which may have introduced confounding. Goddard et al. found no statistically significant differences in hearing at an average of 12.7 months post-operatively in 23 cases of surgically repaired SSCD via the MCF approach (25). Our study did not find a statistically significant change in BC PTA after SSCD repair via the TM approach (4.5 dB, 95% CI: −3, 8, W=13, P=0.188, r_rb=−0.73), however, the sample size was small (n=5). Banakis Hartl et al. investigated hearing outcomes after TM plugging for SSCD in 19 cases. They also found no statistically significant differences in BC PTA; however, they only examined audiometric outcomes at 250 and 500 Hz (26).

Our study did not find a statistically significant change in BC PTA after PCO (−1 dB, 95% CI: −12, 10, W=7, P=1.0, r_rb=0.07), albeit the sample size was small (n=5). Hearing outcomes after PCO are infrequently reported in the literature given the rarity of the procedure (17,27-29). An aforementioned study by Lin et al. did not find a statistically significant change in air or BC PTA postoperatively, but did report a single case of 25 dB SNHL after PCO (23). An early review in 2001 by Agrawal et al. found three cases of long-term hearing loss after occlusion of 44 ears in 42 patients. One patient was found to have persisting 85 dB SNHL, one patient had a flat 20 dB drop in bone conduction thresholds and one patient with a 20 dB isolated high frequency loss (4). A 2019 systematic review by Maas et al. found transient conductive or SNHL in nearly all patients post-operatively (30). A total of 15 patients (8%) experienced permanent SNHL due to surgery. Two patients had a Barany deaf ear (>100-dB hearing loss). Nine patients (5%) experienced persistent mild hearing loss, one of which was caused by a dislocation of the incus.

Our study revealed a worsening BC PTA in 23 of 32 cases (72%), albeit 19 (59%) reported <10 dB of hearing loss. Four of the 32 cases (12.5%) reported SNHL between 11–40 dB. There were no cases of worsening BC PTA >40 dB. The MCF approach was most reported (n=17), however, this is likely due to the unequal sample sizes between subgroups. Lin et al. reported long term SNHL of 25 dB in one PCO case, and one case of profound SNHL of >55 dB after the MCF approach (23).

The MCF approach was utilised in 22 of the 27 SSCD procedures. All 22 cases had significant tegmen defects, which included multiple defects or a thin tegmen, or a large semicircular canal dehiscence which was best addressed by an MCF approach. Although to a lesser extent, a similar study by Lin et al. reported a predominance of MCF procedures for SSCD repair (43 of the 72 SSCD procedures); however, the rationale behind the choice of surgical approach was not described (23).

There were several limitations that should be considered when interpreting our findings. Firstly, our retrospective case series lacked a control group. There were also differences in the mean age of each subgroup, with the patients in the PCO subgroup being older than SSCD subgroups. Due to the retrospective nature of the study, the timing of data collection was not standardised. While most post-operative audiograms were collected approximately two months after procedure, this was not the case for all patients. Assessment of audiological outcomes over a longer post-operative period may yield different results. This study did not assess the relationship between symptom resolution and the rate of SNHL post-procedure. There was also an unequal sample size between the SSCD and BPPV groups which may lead to skewing of the data in a pooled analysis. With these limitations in mind, our findings should be interpreted with caution.

We recommend future studies utilise a prospective study design with complete audiometric data collected at prespecified intervals and larger sample sizes to minimise uncertainty surrounding hearing outcomes after SSCD repair and PCO. Studies should also include a control group comprising of patients with SSCD or BPPV who do not receive surgical intervention. Further subgroup analysis should be performed for age and symptom resolution. Head-to-head comparisons with similar sample sizes are required to assess which surgical approach for SSCD repair gives the best audiologic outcomes while providing symptom resolution.

Conclusions

In this study, SSCD repair and SSCD repair via an MCF approach were associated with a statistically significant SNHL of <5 dB, a finding that should be discussed with patients during pre-operative counselling. Sensorineural hearing outcomes for SSCD repair via the TM approach and PCO for BPPV were not statistically significant.

Acknowledgments

None.

Footnote

Reporting Checklist: The authors have completed the STROCSS reporting checklist. Available at https://www.theajo.com/article/view/10.21037/ajo-25-23/rc

Data Sharing Statement: Available at https://www.theajo.com/article/view/10.21037/ajo-25-23/dss

Peer Review File: Available at https://www.theajo.com/article/view/10.21037/ajo-25-23/prf

Funding: None.

Conflicts of Interest: All authors have completed the ICMJE uniform disclosure form (available at https://www.theajo.com/article/view/10.21037/ajo-25-23/coif). The authors have no conflicts of interest to declare.

Ethical Statement: The authors are accountable for all aspects of the work in ensuring that questions related to the accuracy or integrity of any part of the work are appropriately investigated and resolved. The study was conducted in accordance with the Declaration of Helsinki and its subsequent amendments. The study was approved by the Ramsay Health Care HREC (HREC Reference 2025/ETH/0041). Patient confidentiality was maintained by anonymizing data. The requirement for individual consent was waived as this was a low-risk retrospective review.

Open Access Statement: This is an Open Access article distributed in accordance with the Creative Commons Attribution-NonCommercial-NoDerivs 4.0 International License (CC BY-NC-ND 4.0), which permits the non-commercial replication and distribution of the article with the strict proviso that no changes or edits are made and the original work is properly cited (including links to both the formal publication through the relevant DOI and the license). See: https://creativecommons.org/licenses/by-nc-nd/4.0/.

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