Discussion

We describe herein our experience with setting up a new service to provide transmastoid plugging of dehiscent semicircular canal and the initial results. Superior semicircular canal dehiscence remains a relatively novel condition, and good results have been described with the middle cranial fossa approach as well as the transmastoid approach to plugging or resurfacing of the dehiscent semicircular canal.^{Reference Bi, Brewster, Poe, Vernick, Lee and Corrales2,Reference Beyea, Agrawal and Parnes5,Reference Amoodi, Makki, McNeil and Bance9–Reference Goddard and Wilkinson11} The middle cranial fossa approach is primarily used in neurosurgical units. The transmastoid procedure is suited to most otologists because of familiarity with the approach,^{Reference Allsopp, Kim, Robbins, Page and Dornhoffer3,Reference Beyea, Agrawal and Parnes5} and the procedure can be performed in any ENT unit and avoids the risks of craniotomy.

Not every dehiscent semicircular canal requires surgical intervention. Conservative management with avoidance of provocative stimuli is chosen by many patients once the condition is explained to them. Surgery is reserved for cases of intractable or debilitating symptoms. Symptomatic improvement following surgical intervention has been reported for all approaches.^{Reference Bi, Brewster, Poe, Vernick, Lee and Corrales2,Reference Beyea, Agrawal and Parnes5,Reference Amoodi, Makki, McNeil and Bance9–Reference Goddard and Wilkinson11} The middle cranial fossa approach is the original technique described by Minor et al. and is the traditional approach for which the most data is available.^{Reference Ward, Agrawal, Nguyen, Della Santina, Limb and Francis12} Proponents of this approach argue it offers a more extensive visualisation of the dehiscence and is safer in challenging cases where there may be a poorly pneumatised temporal bone, extensive tegmen defects or a low-lying temporal fossa.^{Reference Bi, Brewster, Poe, Vernick, Lee and Corrales2}

On the other hand, the transmastoid approach avoids the morbidity of a craniotomy and has a higher patient acceptance.^{Reference Schwartz, Almosnino, Noonan, Banakis Hartl, Zeitler and Saunders13} This approach is of interest to otologists as the transmastoid approach is familiar territory. A systematic review from 2017 showed that transmastoid plugging, when compared with the middle cranial fossa approach, reduced hospital stay, complication rates and revision rates.^{Reference Ziylan, Kinaci, Beynon and Kunst14} More than 90 per cent of patients report improvement in vestibular and hearing symptoms following semicircular canal plugging via a transmastoid approach (bone pâté or temporalis fascia).^{Reference Beyea, Agrawal and Parnes5}

A systematic review of 20 studies and 150 cases found no significant statistical difference in terms of success rate and surgical complications between approach (transmastoid vs middle cranial fossa) and modalities of surgery (plugging, capping, resurfacing and plugging with resurfacing).^{Reference Gioacchini, Alicandri-Ciufelli, Kaleci, Scarpa, Cassandro and Re15} There are several studies that report higher success rates for plugging as compared with canal resurfacing,^{Reference Minor16} and a meta-analysis encompassing 64 operations found higher success rates for plugging and capping techniques when compared with canal resurfacing.^{Reference Vlastarakos, Proikas, Tavoulari, Kikidis, Maragoudakis and Nikolopoulos17}

We set up a surgical transmastoid superior semicircular canal dehiscence service in a busy otology unit. The procedure underwent approval by the Trust’s new intervention guidance committee. Support and proctorship were elicited (and kindly provided) from the senior surgeon (RI). Patients were provided with comprehensive information about the middle cranial fossa and transmastoid approaches and offered the option of referral to a lateral skull base or neurosurgical centre if they preferred the middle cranial fossa approach or if the temporal bone anatomy (as assessed on the pre-operative CT scan) precluded the transmastoid approach.

In our initial series, all three patients underwent transmastoid superior semicircular canal dehiscence repair successfully. No immediate post-operative complications occurred and hearing was preserved. One patient developed benign paroxysmal positional vertigo that responded to the Epley manoeuvre; this has been described to occur following superior semicircular canal dehiscence surgery previously.^{Reference Barber, Cheng, Owoc, Lin, Remenschneider and Kozin18} Pre-operative and post-operative patient symptom scores demonstrated improvement in symptoms post-operatively (Table 1). Interestingly, all symptoms showed improvement in scores with the exception of ‘fullness in the ear’, which tended towards persistence despite surgery. All patients in our series demonstrated an improvement in quality-of-life outcomes following transmastoid superior semicircular canal dehiscence (Table 3). This improvement encompassed general quality-of-life measures as opposed to those specific to social support and physical health measures (Table 3).

Limited data is currently available in literature on the patient-reported outcomes of superior semicircular canal dehiscence surgery. In our experience, pre-operative and post-operative recording of patient outcomes is very helpful in assessing the surgical results and also providing patients with a measurable readout of their symptom improvement. Our data has the limitation of being a small series but nevertheless demonstrates a clear benefit in terms of patient-reported outcomes. The lack of a validated disease-specific outcome measure for superior semicircular canal dehiscence renders it difficult to objectively delineate outcomes.^{Reference Ward, Carey and Minor4} In addition to patient questionnaires, we also propose the routine use of post-operative vestibular-evoked myogenic potentials to document improvement in vestibular-evoked myogenic potential thresholds as a measure of effective plugging of superior semicircular canal dehiscence.