Superior Semicircular Canal Dehiscence Repair With Hydroxyapetite Cement via a Transmastoid Approach

ABSTRACT

Introduction

The aim of this study was to assess the efficacy of superior semicircular canal dehiscence (SSCD) repair via a transmastoid approach using hydroxyapatite bone cement capping.

Methods

This retrospective case series was carried out at a tertiary referral center. All patients were ≥ 18‐years‐old diagnosed with SSCD between 2012 and 2022 and underwent a transmastoid approach implementing hydroxyapatite capping. Dehiscence location and size were assessed by reviewing preoperative CT temporal bone scans and correlated to the success rate of surgical repair. The failure rate (lack of symptom resolution and/or persistent dehiscence on postoperative imaging) and/or need for revision surgery were evaluated.

Results

Twenty‐two patients (25 ears) were included. Mean age was 50.8 years (SD = 9.9 years) with 50.0% female patients (n = 11). The predominant location of SSCD was determined as apical (76.0%, n = 19), followed by anterior limb (12.0%, n = 3) and posterior limb (12.0%, n = 3). Mean dehiscence size was 2.8 mm (SD = 1.4 mm). Median follow‐up time after repair was 9.0 months (interquartile range: 2–36 months). Failure rate was 8.0% (n = 2). Both cases demonstrated persistent SSCD on postoperative imaging; one case had a residual apical dehiscence of 1.6 mm persistent at 4 months, and one had a posterior‐apical dehiscence of 2.3 mm persistent at 8 months after surgery.

Discussion

Transmastoid approach for SSCD repair with hydroxyapatite bone cement capping has a relatively low failure and complication rate, alleviating the need for middle fossa approach. To our knowledge, this case series represents the largest for this approach and material combination for SSCD repair, demonstrating that transmastoid repair with bone cement represents a promising approach for effective management of patients with SSCD.

Level of Evidence

4.

The objective of this study was to assess the utility of SSCD repair via a transmastoid approach using hydroxyapatite bone cement. In this cohort, there was no statistically significant worsening of sensorineural hearing loss and 70% had resolution of their preoperative air‐bone gap. This suggests that a transmastoid repair of SSCD using bone cement is both safe and effective.

1. Introduction

Superior semicircular canal dehiscence (SSCD) was first described in 1998 by Minor et al. [1] Although this pathology was recognized less than 25 years ago, several surgical techniques for treating SSCD have been and are still actively being developed [2]. The pathologic third opening in SSCD alters the pressure gradient in the inner ear, leading to a range of symptoms, such as autophony, pulsatile tinnitus, Tullio phenomenon, etc., that can be debilitating and impede quality of life [3, 4, 5]. The etiology of SSCD is thought to be due to variations in thickness of the bone that interjects the superior semicircular canal from the dura mater of the brain, predisposing some individuals with thinner bone in that area to disruption and dehiscence during their lifetime [3, 6]. The prevalence of SSCD has been reported to be 0.5%–9% [6, 7]. However, the full spectrum of presentation of the disease is even more rare, indicating that many people have subclinical SSCD [3].

Surgery has been shown to be most effective in treating auditory symptoms, while dizziness and imbalance are more likely to persist after surgery [2]. The decision to treat SSCD surgically is based upon the subjective severity of symptoms and impact on patients' quality of life. For those patients who choose to undergo surgery, the middle fossa and transmastoid approaches have been most commonly described; however, the literature comparing these techniques remains scarce [8]. The middle fossa approach allows for direct visualization of the dehiscence and may have a lower risk of sensorineural hearing loss or loss of vestibular function in other canals [9, 10]. However, this approach carries the risk of temporal lobe retraction with increased risk of CSF leak or intracranial bleed [11]. In comparison, the transmastoid approach avoids craniotomy and temporal lobe retraction, which is better suited for elderly patients [12]. However, the proximity to the vestibule creates a possible increased risk of hearing loss and vestibular dysfunction post‐operatively. Repair of the dehiscence can be achieved through resurfacing, plugging, capping, or alternatively can be addressed by reinforcement of the round or oval window [10, 13].

While revision surgery for failed repair or incomplete resolution of symptoms can improve patients' quality of life, revision surgery has been associated with an increased risk of CSF leak and less favorable outcomes than initial surgery [14, 15]. Previous studies have explored factors associated with the failure of surgical treatment of SSCD [15]. Given the number of approaches for access, materials, and repair, it is hard to assess and compare the different approaches effectively. Assessing the efficacy of a consistent combination is valuable in our attempt to optimize management and guide tailored treatment. Our study evaluated the efficacy of SSCD repair via a transmastoid approach using hydroxyapatite bone cement capping. A better understanding of the efficacy of this approach and technique in repairing SSCD and skull base defects can help guide future surgical practice to allow improved patient care and outcomes.

2. Methods

This study was deemed exempt by the Yale University Institutional Review Board (IRB protocol ID #: 2000032898). Patients ≥ 18 years of age with a diagnosis of superior semicircular canal dehiscence (SSCD) from January 2012 until June 2022 were retrospectively identified by the hospital data analytics team using the following International Classification of Diseases (ICD)‐9 codes (386.4, 386.5, 386.8, 386.9) and ICD‐10 codes (H83.8X9, H81, H82, H83). Exclusion criteria included: (1) surgical repair of SSCD was not completed; (2) a transmastoid approach for SSCD repair was not implemented; (3) hydroxyapatite bone cement was not utilized for the repair. Stryker HydroSet bone cement was used in all SSCD repairs in this study. Hydroxyapatite cement is not currently FDA approved for use in the inner ear. Therefore, this use of HydroSet bone cement for SSCD repair is an off‐label use.

Medical record review was conducted to obtain patient demographic information, comorbidities, surgical variables, and outcome details. Demographic information included sex and age at the time of surgery. Surgical variables included surgical side (right or left ear), defect size, and location. Defect size was measured on preoperative high‐resolution reformatted temporal bone CT scans with a thickness of 0.625 mm. Coronal, sagittal, Stenver, and Poschl views were utilized for the measurements of the defects. Preoperative symptoms were evaluated, including reported autophony, pressure‐induced dizziness, Tullio phenomenon, aural fullness, abnormal perception of own voice, subjective hearing loss, tinnitus (pulsatile or non‐pulsatile, if specified), and vertigo, which were coded only if there was specific mention in consultation or progress notes by medical personnel. Corresponding postoperative symptoms were coded only if specifically mentioned in follow‐up notes. Postoperatively, the success of surgery was determined through review of postoperative imaging and review of follow‐up appointment documenting symptomatic resolution. Chart review was completed to assess complications and revision rates.

Audiologic data was gathered and analyzed. Pre‐operative and post‐operative audiograms were used to determine pure tone thresholds (PTTs) at 250, 500, 1000, and 2000 Hz. Changes in preoperative to postoperative PTTs were calculated at each frequency. Paired t‐tests were conducted for the changes in the PTTs at each frequency to assess for significant changes postoperatively. Changes in preoperative and postoperative air‐bone gap (ABG) were also calculated.

Categorical variables were reported as numerical counts and percentages. Continuous variables were reported as mean values with standard deviations (if normal distribution) and median values with interquartile ranges (IQR) if data were not normally distributed. Analyses were conducted in GraphPad Prism (version 9.2.0; GraphPad Software, San Diego, CA, USA).

After completing a tympanomastoidectomy, the tegmen plate is skeletonized, removing the bone from the middle cranial fossa dural plate down to the level of the labyrinth. After achieving hemostasis, the middle cranial fossa is decompressed, and the bony labyrinth is skeletonized, removing the perilabyrinthine air cells around the lateral canal and exposing the posterior canal. The posterior canal is followed to the common crus region, where the superior canal is identified. Once the superior canal is completely skeletonized, a Freer dissector is used to gently elevate the dura further anterior to the superior semicircular canal so that the whole canal can be accessed with hydroxyapatite bone cement. A neurosurgical cottonoid is inserted over the superior canal against the dura to provide better access for cementing.

The hydroxyapatite bone cement is prepared following the manufacturer's recommendations. With a dedicated syringe, the cement is gradually applied over the superior semicircular canal while the dura is elevated away from the superior canal. Once the cement is in place, it is gently packed over the canal using a neurosurgical cottonoid. This cement is packed over the superior canal twice in this manner. Once the canal is capped with cement, the cement is layered against the dura of the middle cranial fossa and layered up to the level of the cortex. After each placement of the cement with the use of a neurosurgical cottonoid and suction, the cement is compressed and allowed to set for approximately 30 s before placing another layer. This is progressively completed until the superior semicircular canal defect and the tegmen are completely covered. No other materials such as fascia or cartilage are used. Neurosurgical cottonoid is used to compress and dry the cement concurrently. The cement is allowed to dry for 5–10 min, and then the repair is inspected, and a Valsalva maneuver is completed to ensure that there is no CSF leak. The wound is observed for 10–15 min intraoperatively prior to closure.

3. Results

A total of 22 patients, comprising 25 ears, were included for analysis. The mean age at the time of surgery was 50.8 years (standard deviation (SD) = 9.9 years), and 50.0% of patients were female (n = 11). Preoperatively, 59.1% (n = 13) of patients were found to experience autophony, 13.6% (n = 3) pressure‐induced dizziness, 13.6% (n = 3) were found to have Tullio phenomenon, 36.4% (n = 8) reported aural fullness, 18.2% (n = 4) reported abnormal perception of their own voice, 50.0% (n = 11) reported subjective hearing loss, 50.0% (n = 11) reported tinnitus (pulsatile or non‐pulsatile), and 45.5% (n = 10) reported vertigo. Postoperatively, no patients were found to have autophony, Tullio phenomenon, or abnormal perception of their own voice. Residual symptoms included aural fullness that was described in 31.8% (n = 7) of patients postoperatively, 31.8% (n = 7) experienced subjective hearing loss and tinnitus, and 27.3% (n = 6) experienced vertigo postoperatively. Importantly, none of the patients without subjective hearing loss preoperatively endorsed any subjective hearing loss postoperatively.

In our cohort, 60.0% (n = 15) of surgical repairs were of the left ear and 40.0% (n = 10) for the right ear (of these, three were bilateral repairs). In terms of dehiscence location of the superior canal, 76.0% (n = 19) had apical dehiscence, 12.0% (n = 3) had anterior limb dehiscence, and 12.0% (n = 3) had posterior limb dehiscence. Mean dehiscence size was 2.8 mm (SD = 1.4 mm). Median follow‐up time after repair was 9.0 months (IQR: 2–36 months). A successful repair was determined on postoperative CT scan and resolution of symptoms. An example of a successful SSCD repair demonstrated by postoperative imaging is presented in Figure 1.

FIGURE 1.

Pre‐operative (A) and post‐operative (B) coronal CT scans demonstrating SSCD defect and successful repair with hydroxyapatite bone cement capping.

Preoperative and postoperative audiograms were collected. Fifteen patients successfully completed both preoperative and postoperative audiograms and were included in this portion of the analysis. There was a statistically significant improvement between preoperative and postoperative PTTs at 250 Hz (average of 35.6 dB vs. 29.1 dB, p = 0.020). There were no significant differences between preoperative and postoperative PTTs at 500 Hz (34.7 dB vs. 33.4 dB, p = 0.510), at 1000 Hz (35.9 dB vs. 34.7 dB, p = 0.657), and at 2000 Hz (37.8 dB vs. 37.8 dB, p = 1). There was also no significant difference between the preoperative and postoperative pure tone average (36.1 dB vs. 35.3 dB, p = 0.724). Ten of the fifteen patients had a preoperative conductive hearing loss with an ABG ranging between 10 and 30 dB (median: 15 dB, IQR: 10–25 dB). Seven of these 10 patients had complete resolution of their conductive hearing loss, and three patients had a residual ABG postoperatively, albeit an improvement in the pure tone threshold.

Failure rate was 8.0% (n = 2); no revision surgeries were needed due to either adequate symptom control or relatively limited follow‐up time. Both cases demonstrated persistent SSCD on postoperative imaging. One case had a residual apical dehiscence of 1.6 mm persistent at 4 months postoperatively, and one had a posterior‐apical dehiscence of 2.3 mm persistent at 8 months after surgery.

4. Discussion

In this study, we examined the efficacy of SSCD repair via a transmastoid approach using hydroxyapatite bone cement capping. We found a relatively low failure rate of 8.0% (n = 2) with this technique and material combination; no revision surgeries were needed, which was attributed to either adequate symptom control or relatively limited follow‐up time. To our knowledge, the present case series represents the largest of its kind for this approach and material combination for SSCD repair.

At present, there is no consensus on the best surgical technique or material for the repair of SSCD. Much of the literature presents data on SSCD repair, often with wide variability of approach, technique, and material, sometimes in the same study, making it challenging to draw conclusions. In our study, we sought to assess the efficacy and safety of the transmastoid approach. Previous studies have suggested that the transmastoid approach might afford lower complication and revision rates, as well as shorter hospital stays when compared to the alternative middle fossa approach [8, 16]. The results of our study are consistent with some of these aforementioned findings given the low rate of unsuccessful repair. The transmastoid approach does mitigate the need for significant temporal lobe retraction, which in the elderly population is imperative, and therefore should be considered the preferred approach, especially in this population. However, there is evidence to support superior hearing outcomes with the middle fossa approach due to the better exposure it delivers [17]; thus, further studies optimizing hearing outcomes with the transmastoid approach are necessary. In our study, patients were noted to have either stable or improved hearing. In our cohort, we did not find any statistically significant decreases in PTA or PTT, confirming that there was not any worsening sensorineural hearing loss when using hydroxyapatite cement via a transmastoid approach. Furthermore, in our cohort, 70% of patients with preoperative ABG had complete resolution of their ABG after surgery.

The material used for the repair is an additional imperative factor in evaluating SSCD repair. We evaluated the outcomes of the use of hydroxyapatite cement as the repair material. To our knowledge, this is the first study to assess the use of this material via a transmastoid approach. The use of hydroxyapatite as a synthetic material for skull base repair is increasingly investigated. Previous studies have found that it allows for a shorter operating time when compared to other autologous materials with similar success rates, likely due to its rapid‐setting abilities and compliancy as a material [18]. Currently, there is limited data on the ototoxicity of hydroxyapatite cement in the inner ear, specifically related to direct contact of hydroxyapatite cement on the membranous labyrinth. The lack of worsening hearing outcomes in this cohort suggests minimal ototoxicity of hydroxyapatite cement capping for SSCD repair. Another common concern for using hydroxyapatite is the risk for local infection. However, our study demonstrates the safety of this material given that no patients in our cohort experienced postoperative complications or infections. Further investigations in larger cohorts can validate our findings and promote the use of hydroxyapatite cement for repair of SSCD.

The treatment of SSCD also includes a variety of repair techniques such as capping, plugging, and resurfacing of the dehiscence. Plugging involves the obliteration of the dehiscent canal using bone pâté, and resurfacing involves covering the dehiscence using cartilage and fascia without occluding the canal. Capping is a modified version of resurfacing that uses hydroxyapatite instead [19, 20]. While capping for SSCD has been studied in patients using the middle cranial fossa approach, our study is the first to investigate its use with the transmastoid approach. Here, we demonstrate that this technique via the transmastoid approach is, in fact, successful and can be a safe and effective alternative, given a low failure rate of 9%. The plugging technique has been shown to have a higher rate of rupture of the endolymphatic duct in the superior canal due to the need for more aggressive manipulation. On the other hand, failures associated with resurfacing are due to the dislocation and absorption of the material [19]. The technique of capping shows more promise given that it is not an absorbable material and is much less likely to dislocate. The capping technique with the use of hydroxyapatite cement is an especially compelling approach when implemented through the less invasive transmastoid approach.

The present study has several limitations. The data were collected retrospectively, which exposes the results to inherent biases. This was mitigated by the utilization of our hospital data analyst team, which performs a comprehensive search of the hospital data for patients and is not involved in any part of the analysis. Additionally, because data was collected retrospectively from medical records and notes, symptoms experienced but not described by patients without elicitation may have been missed; these occurrences may have contributed to reporting bias. SSCD remains a disease with relatively low prevalence, and therefore, our study is subject to the limitations of a small sample size; multi‐institutional collaborations and pooling of data would be particularly beneficial. There was a wide range of follow‐up length (2 to 36 months) after surgery, which may be an important limitation given the dynamic nature of symptoms postoperatively.

Given these limitations, future research efforts are needed to continuously assess the various surgical techniques, repair materials, and outcomes measures for SSCD management. Prospective studies, particularly those that compare different access techniques with consistent repair materials across multiple institutions, would be valuable for guiding treatment practices. Incorporation of pre‐ and post‐operative quality of life assessments, in addition to the imaging findings, would be especially valuable to examine the efficacy of surgical treatment options on symptom resolution.

5. Conclusions

Transmastoid approach for SSCD repair with hydroxyapatite bone cement capping has a high success rate and a low rate of complications. This approach may alleviate the need for the wider and more invasive exposure of the middle fossa approach. The combination of hydroxyapatite capping via the transmastoid approach affords a less invasive, effective, and safe technique for effective management of patients with SSCD. Future prospective studies with larger multi‐institutional cohorts and quality of life assessments are needed to further substantiate the efficacy of this approach for SSCD management and continuously improve patient care.

Conflicts of Interest

The authors declare no conflicts of interest.