Systematic Review of Round Window Operations for the Treatment of Superior Semicircular Canal Dehiscence

The impact of round window reinforcement on middle and inner ear mechanics with air and bone conduction stimulation

The round window (RW) membrane plays an important role in normal inner ear mechanics. Occlusion or reinforcement of the RW has been described in the context of congenital anomalies or after cochlear implantation and is applied as a surgical treatment for hyperacusis. Multiple lumped and finite element models predict a low-frequency hearing loss with air conduction of up to 20 dB after RW reinforcement and limited to no effect on hearing with bone conduction stimulation. Experimental verification of these results, however, remains limited. Here, we present an experimental study measuring the impact of RW reinforcement on the middle and inner ear mechanics with air and bone conduction stimulation. In a within-specimen repeated measures design with human cadaveric specimens (n = 6), we compared the intracochlear pressures in scala vestibuli (PSV) and scala tympani (PST) before and after RW reinforcement with soft tissue, cartilage, and bone cement. The differential pressure (PDIFF) across the basilar membrane - known to be closely related to the hearing sensation - was calculated as the complex difference between PSV and PST. With air conduction stimulation, both PSV and PSTincreased on average up to 22 dB at frequencies below 1500 Hz with larger effect sizes for PST compared to PSV. The PDIFF, in contrast, decreased up to 11 dB at frequencies between 700 and 800 Hz after reinforcement with bone cement. With bone conduction, the average within-specimen effects were less than 5 dB for either PSV, PST, or PDIFF. The inter-specimen variability with bone conduction, however, was considerably larger than with air conduction. This experimental study shows that RW reinforcement impacts air conduction stimulation at low frequencies. Bone conduction stimulation seems to be largely unaffected. From a clinical point of view, these results support the hypothesis that delayed loss of air conduction hearing after cochlear implantation could be partially explained by the impact of RW reinforcement.

Posterior Semicircular Canal Dehiscence with Vestibulo-Ocular Reflex Reduction for the Affected Canal at the Video-Head Impulse Test: Considerations to Pathomechanisms

Posterior semicircular canal dehiscence (PSCD) has been demonstrated to result in a third mobile window mechanism (TMWM) in the inner ear similar to superior semicircular canal dehiscence (SSCD). Typical clinical and instrumental features of TMWM, including low-frequency conductive hearing loss (CHL), autophony, pulsatile tinnitus, sound/pressure-induced vertigo and enhanced vestibular-evoked myogenic potentials, have been widely described in cases with PSCD. Nevertheless, video-head impulse test (vHIT) results have been poorly investigated. Here, we present six patients with PSCD presenting with a clinical scenario consistent with a TMWM and an impaired vestibulo-ocular reflex (VOR) for the affected canal on vHIT. In two cases, an additional dehiscence between the facial nerve and the horizontal semicircular canal (HSC) was detected, leading to a concurrent VOR impairment for the HSC. While in SSCD, a VOR gain reduction could be ascribed to a spontaneous "auto-plugging" process due to a dural prolapse into the canal, the same pathomechanism is difficult to conceive in PSCD due to a different anatomical position, making a dural herniation less likely. Alternative putative pathomechanisms are discussed, including an endolymphatic flow dissipation during head impulses as already hypothesized in SSCD. The association of symptoms/signs consistent with TMWM and a reduced VOR gain for the posterior canal might address the diagnosis toward PSCD.

Long-Term Outcomes of Round Window Reinforcement for Superior Semicircular Canal Dehiscence Syndrome

OBJECTIVE

To report long-term patient reported outcome measures (PROMs) after standardized round window rein-forcement (RWR) with thin cartilage and perichondrium for superior semicircular canal dehiscence syndrome (SSCDS).

METHODS

Cross-sectional survey in 2020 and retrospective longitudinal study of outcomes at 3 months, 1 year, and last follow-up after 28 consecutive RWRs. Endpoints were the last follow-up for PROMs and 1 year postoperatively for audiometry and cVEMP.

RESULTS

At the last follow-up (mean 2.4 years postoperatively), improvement was reported for 19/28 ears (68%) in symptoms overall; for 17/27 ears (63%) in auditory symptoms, and for 12/24 (50%) in vestibular symptoms. Nine ears (32%) required further surgery. No major complications occurred. On the group level, postoperative improvement at 3 months declined significantly for auditory and vestibular symptoms over time, and stayed stable beyond 1 year. Improved ears had on average 2.9 years follow-up. Improvement correlated significantly with SSCD length, and was associated with contralateral dehiscence. Thirteen ears (46%) had another potential cause of vestibular symptoms. This group showed significantly less improvement. Audiometric test results did not predict PROMs.

CONCLUSIONS

Since long-term outcomes do not compare with those reported for plugging and repair, RWR is not suggested as a first line intervention for SSCDS. Considering the stable rates of improvement on average 2.9 years postoperatively and the absence of major complications, RWR may be an alternative to plugging or repair in fragile patients who do not accept the risk of complications with more invasive surgery, and who accept that results may deteriorate over time.

Transmastoid Occlusion Surgery for Superior Semicircular Canal Dehiscence Syndrome Improves Patient-Reported Quality-of-Life Measures and corrects cVEMP Thresholds and Amplitudes

OBJECTIVE

To determine the pre- and postoperative clinical, audiological, vestibular, and patient-reported measures in patients undergoing transmastoid occlusion surgery for superior canal dehiscence syndrome (SCDS).

STUDY DESIGN

Retrospective case review.

SETTING

Tertiary referral centre, UK.

PATIENTS

All primary transmastoid occlusion surgeries for SCDS were included (tertiary centre, single-surgeon), January 2008 to July 2019.

INTERVENTIONS

Transmastoid superior canal occlusion surgery for SCDS.

MAIN OUTCOME MEASURES

We collated audiological (pure tone audiogram), vestibular (cervical vestibular evoked myogenic potentials [cVEMPs]), and patient-reported outcome measures (Dizziness Handicap Inventory and subjective symptom grading).

RESULTS

Fifty-two patients (55 ears) met the inclusion criteria. Thirty-one (56%) were female. Mean age was 47 years (range 29-63) and mean follow-up of 11.2 months. Six patients had bilateral disease, four of whom underwent sequential, bilateral surgery.Autophony was the most frequent presenting symptom, improving in 92%.Significant improvements were self-reported in patients' autophony (p < 0.0001), pressure- and noise-induced dizziness (p < 0.0001 and p < 0.0001), aural fullness (p = 0.0159), pulsatile tinnitus (p < 0.0001), perceived hearing loss (p = 0.0058), and imbalance (p = 0.0303).Overall Dizziness Handicap Inventory scores reduced from 45.9 to 27.4 (p < 0.0001), and across all subgroups of functional (p = 0.0003), emotional (p < 0.0001), and physical handicap (p = 0.0005).A 6.4-dB HL improvement in the air-bone gap (500-1000 Hz) occurred (95% confidence intervals 3.3-9.4 dB HL, p < 0.0001). There were no dead ears. cVEMP thresholds, when recordable, normalized in all except two ears.

CONCLUSIONS

Transmastoid occlusion is effective at improving patient-reported outcomes and normalizing cVEMP thresholds, though some symptoms, notably disequilibrium, persist to a variable degree.

Surgical treatments of superior semicircular canal dehiscence: A single-centre experience in 63 cases

OBJECTIVE

Different procedures have been described to treat superior canal dehiscence. The present study aims to describe the results obtained with middle fossa approach, transmastoid approach, and round window reinforcement in a large series of patients.

METHODS AND DESIGN

In this single-center retrospective study, we report the results of the procedures performed between 2006 and 2019 using the three main surgical approaches, middle fossa approach (MFA), transmastoid approach (TMA), and round window reinforcement (RWR). The outcome on cardinal cochlear and vestibular symptoms, audiometric results, and changes in cervical vestibular evoked myogenic potentials (cVEMPs) were analyzed. The patients were also interviewed 12 months to 13 years post-treatment to establish their overall satisfaction following surgery.

RESULTS

Sixty-three patients were divided into three groups: 42 MFA; 12 RWR; 9 TMA. Postsurgical control rates exceeded 80% for the majority of symptoms in the MFA and TMA groups, and ranged from 11.1% to 83.3% for the RWR group. Over 90% of MFA or TMA patients and 60% of the RWR cohort were satisfied overall with their treatment. Hearing thresholds were intact following surgery in the MFA and TMA groups. There was one case of profound postoperative deafness in the RWR group.

CONCLUSION

MFA and TMA are both safe and effective techniques in the treatment of disabling SSCD. Since MFA is the more invasive technique, we suggest that TMA should be proposed as first-line treatment, temporal bone anatomy permitting. RWR outcomes are more variable in term of symptomatic control, and this option could be offered to patients at risk under general anesthesia.

LEVEL OF EVIDENCE

Level 4 evidence.

Transmastoid Superior Semicircular Canal Plugging: A Prospective Analysis of Surgical Outcomes

OBJECTIVES

To assess the outcomes of the transmastoid superior semicircular canal plugging in patients with superior semicircular canal dehiscence (SSCD).

STUDY DESIGN

Prospective cohort study.

SETTING

Tertiary, university center.

PATIENTS

Patients with SSCD undergoing transmastoid superior semicircular canal plugging within a 30-month period.

INTERVENTIONS

Transmastoid superior semicircular canal occlusion.

MAIN OUTCOME MEASURES

We documented the surgical technique, pre- and postoperative (3-month review) dizziness handicap inventory scores, average hearing thresholds, low-frequency air-bone gap, six-canal video head-impulse-test responses, improvement of the auditory symptoms and complications.

RESULTS

Out of 30 patients with SSCD, 11 patients (12 ears) were enrolled with an average age 41.17 years (range 32-65 years). Oscillopsia resolved in all patients; DHI score improved from 56.7 (range 22-84) preoperatively to 25.83 (10-46) postoperatively (p = 0.001), while out of the nine patients with troublesome auditory symptoms, five patients noticed an improvement. The average pre- and postoperative hearing thresholds were 15.2 dB (range 3-32.5 dB) and 14.17 dB (range 5-30 dB) (p = 0.73), respectively. The average pre- and postoperative low-frequency air bone gap was 12.3 dB (range 5-20 dB) and 9.4 dB (range 0-20 dB), respectively (p = 0.24) (Table 1). There were no major complications; two patients developed postoperative benign paroxysmal positional vertigo.

CONCLUSION

Transmastoid plugging of the superior semicircular canal can safely and significantly improve the vestibular symptoms of the patients with SCDS, as well as the auditory symptoms in a substantial number of patients in a hearing-preservation way.