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LITERATURE REVIEW J Neurosurg 127:1268–1276, 2017

Superior semicircular canal dehiscence syndrome

Wenya Linda Bi, MD, PhD,1 Ryan Brewster, BA,1 Dennis Poe, MD,2,3 David Vernick, MD,3 Daniel J. Lee, MD,3–5 C. Eduardo Corrales, MD,3,5 and Ian F. Dunn, MD1

1Center for Skull Base and Pituitary Surgery, Department of Neurosurgery, Brigham and Women’s Hospital; 2Department of Otolaryngology and Communication Enhancement, Boston Children’s Hospital; 3Department of Otolaryngology, Harvard Medical School; 4Department of Otolaryngology, Massachusetts Eye and Infirmary; and 5Division of Otolaryngology, Brigham and Women’s Hospital, Boston, Massachusetts

Superior semicircular canal dehiscence (SSCD) syndrome is an increasingly recognized cause of vestibular and/or auditory symptoms in both adults and children. These symptoms are believed to result from the presence of a pathologi- cal mobile “third window” into the labyrinth due to deficiency in the osseous shell, leading to inadvertent hydroacoustic transmissions through the and labyrinth. The most common bony defect of the superior canal is found over the arcuate eminence, with rare cases involving the posteromedial limb of the superior canal associated with the superior petrosal sinus. Operative intervention is indicated for intractable or debilitating symptoms that persist despite conserva- tive management and vestibular sedation. Surgical repair can be accomplished by reconstruction or plugging of the bony defect or reinforcement of the through a variety of operative approaches. The authors review the etiology, pathophysiology, presentation, diagnosis, surgical options, and outcomes in the treatment of this entity, with a focus on potential pitfalls that may be encountered during clinical management. https://thejns.org/doi/abs/10.3171/2016.9.JNS16503 KEY WORDS superior semicircular canal dehiscence syndrome; superior semicircular canal; loss; dizziness; transtemporal repair; transmastoid approach; skull base

uperior semicircular canal dehiscence (SSCD) syn- tentials (VEMPs), and confirmatory findings on high-res- drome has been an increasingly recognized cause of olution CT (HRCT) scans. Operative intervention is indi- vestibular and/or auditory symptoms in both adults cated for intractable or debilitating symptoms that persist Sand children since its initial description less than 2 decades despite conservative management and vestibular sedation. ago.60 Patients commonly present with , disequilib- Surgical repair can be accomplished by reconstruction or rium, conductive hyperacusis, autophony, conductive hear- plugging of the bony defect or reinforcement of the round ing loss, pulsatile tinnitus, or aural fullness. Dizziness can window via a variety of operative approaches. We review be associated with sound-induced (Tullio’s phenomenon) the etiology, pathophysiology, presentation, diagnosis, sur- or pressure-induced (Hennebert’s sign) triggers. These gical options, and outcomes in treatment of SSCD, with a symptoms are believed to result from the presence of a focus on potential pitfalls that may be encountered during pathological mobile “third window” into the labyrinth due clinical management. to deficiency in the osseous shell, which possibly results in inadvertent hydroacoustic transmissions through the co- chlea and labyrinth. The most common bony defect of the Epidemiology superior canal is found over the arcuate eminence, with The roof of the SSC is dehiscent in 0.5% and nearly de- rare cases involving the posteromedial limb of the superior hiscent in another 1.4% of cadaveric temporal bone speci- canal associated with the superior petrosal sinus. Symp- mens, localized to either the floor of the middle fossa or toms vary widely from patient to patient, and diagnosis between the SSC and the superior petrosal sinus.18,82 Near is aided by audiometry, vestibular-evoked myogenic po- dehiscence, established at a bone thickness of 0.1 mm or

ABBREVIATIONS ECoG = electrocochleography; HRCT = high-resolution CT; ICP = intracranial pressure; SSC = superior semicircular canal; SSCD = superior semicircu- lar canal dehiscence; VEMP = vestibular-evoked myogenic potential. SUBMITTED February 28, 2016. ACCEPTED September 7, 2016. INCLUDE WHEN CITING Published online January 13, 2017; DOI: 10.3171/2016.9.JNS16503.

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Unauthenticated | Downloaded 09/27/21 12:14 PM UTC Superior semicircular canal dehiscence less in 1 study, compares to an average roof depth of 1 mm HMX3 and POU3F4, Netrin1, cochlin (COCH), and the in control adult specimens.18 Series in which HRCT was solute carrier SLC26A4, to SSCD remains unclear.28,40,71 used have estimated an incidence of SSCD of 3%–10% in both adults and children, which may be an overestimate Pathophysiology given that even HRCT slices are thicker than the thickness of some middle fossa floors.21,23,34,51,63,73,89 Superior semi- Superior semicircular canal dehiscence is hypoth- circular canal dehiscence on one side is also associated esized to cause symptoms by creation of a mobile “third with contralateral thinning or dehiscence in one-third to window.” In normal conditions, the , to which half of all cases on both cadaveric and radiological stud- the footplate attaches, regulates sound input into ies.18,74,92 the , whereas the round window regulates sound and mechanical energy release from the scala tympani of the inner ear, among other functions. These 2 windows Etiology typically direct forces associated with sound waves along The SSC resides under the floor of the middle cranial the spiral . In contrast, the membranous fossa, and is often denoted by the presence of a prominence vestibular labyrinth is insulated from sound or pressure protruding into the floor known as the arcuate eminence. changes in the and CSF by a bony capsule, but In up to 15% of the population, no arcuate eminence is becomes sensitive to such changes if an osseous defect discernible. In other patients, the arcuate eminence may occurs (Fig. 1A and B). Hence, addition of a nonphysi- be rotated posteriorly from the position of the SSC.44 Both ological third window at the roof of the SSC results in congenital and acquired causes of SSCD have been pro- preferential hydroacoustic shunting toward the pathologi- posed. cal bony defect and away from the cochlear partition, to During development, the covering of the SSC grows produce symptoms of vertigo, conductive hyperacusis, or from a diaphanous state to a robust trilaminar capsule be- conductive hearing loss. Transmission of ICP through the tween birth and 3 years of age.18 The SSC also protrudes from the SSCD to the round window prominently into the middle fossa during gestation, com- also produces increased compliance of the inner ear, with pared with a reduced prominent temporal bone location Hennebert’s sign, conductive hearing loss, and the percep- in adults, which may lead to adhesion of the membranous tion of pulsatile tinnitus. labyrinth to dura mater before complete ossification of the The concept of a third window has been conjectured to 78 result in stimuli-induced vertigo in chronic adhesive oti- . A computer simulation model of inner- 20 ear ontogeny has attributed SSCD to a malpositioned tis by disrupting the bony labyrinth. Similar phenomena primitive otocyst and impaired migration of mesenchymal have been observed in dehiscence of posterior and hori- cells to form the apical cap of the canal.82 Failure or inad- zontal from various pathologies such equate osseous development may then manifest in overt as . Animal models, in which the bony apex of the SSC is drilled while preserving the membranous clinical symptoms following a second hit, such as minor 8,16,42 trauma, infection, inflammation, or chronic pressure from labyrinth, corroborate this hypothesis. Fenestration CSF pulsations or the overlying temporal lobe. of the bone overlying selected semicircular canals evokes The presence of SSCD in young children supports a eye and head movements in the plane of the canal with 73 loud noises, producing a sound-induced vestibular activa- congenital etiology. An increasing prevalence of canal 83 dehiscence with age in temporal bone imaging series tion known as the Tullio phenomenon. Removal of the suggests additional acquired factors.30,63 Frequent co- bony cap of the SSC in rodents also produces a signifi- occurrence with tegmen mastoideum and tympani bony cant air-bone gap in response to clicks and a pattern of auditory brain responses, consistent with SSCD findings erosion and the incidence of bilateral SSCD can support 8 either acquired or congenital etiologies. Dehiscence in the in patients. This underlying pathophysiology of an al- posterior semicircular canal and other locations has been tered pressure gradient between mobile window outlets reported, but is much more rare.72 has prompted targeted treatment strategies, as discussed below. Chronic elevated intracranial pressure (ICP) has been hypothesized to underlie co-occurrence of tegmen defects, patulous internal auditory canal, and SSCD, because id- Clinical Presentation iopathic intracranial hypertension is associated with teg- Patients can present with vertigo, disequilibrium, os- men defects and CSF leakage.33,74 Indeed, up to 15% of cillopsia, conductive hyperacusis, autophony, conductive patients undergoing middle fossa craniotomy for repair of hearing loss, hearing distortion, gaze-evoked tinnitus, spontaneous CSF otorrhea are noted to have dehiscence of and aural fullness or blockage.22,47,55,57,81,90,92 A quarter the SSC apex—higher than the reported prevalence in the of patients report an auditory sensation, described as a general population.5 Some patients with SSCD are also “swishing,” associated with motion of the eyes or body, observed to have higher rates of obstructive sleep apnea particularly toward the affected ear. There is an enhanced and a higher body mass index, suggestive of a correlation perception of bone-conducted sounds producing autopho- between elevated ICP and development of dehiscence.64,74 ny of one’s own voice, neck creaking, chewing, and foot- Several families with multiple members who have been steps hitting the ground. As opposed to the autophony of treated for SSCD have been reported.65 However, the con- patulous , there is little or no autophony of tribution of genes implicated in inner-ear development and one’s breathing sounds. Less commonly, dysautonomia, familial deafness syndromes, such as the homeobox genes such as bradycardia and hypotension, may be triggered by

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FIG. 1. Dehiscence of the SSC apical bony labyrinth introduces a mobile third window into the vestibular conduit, leading to perturbation of the normal (A, arrows) to an aberrant state (B, counter arrows). Reconstruction of this osseous defect can be accomplished through resurfacing or capping of the middle cranial fossa floor, including any adjacent tegmen defects C( ; illustrated with a layer of temporalis fascia overlaid by hydroxyapatite) or plugging of the dehiscence (D). Copyright Ryan Brewster. Published with permission. sound or pressure alteration of vestibulosympathetic re- ics produces several localizing signs that aid diagnosis. flexes.58 Unprovoked drop attacks have also been reported Adjunctive testing, including provocative testing, audiom- in isolated cases, with amelioration following SSCD re- etry, electrocochleography (ECoG), and sound-induced pair.14 Symptoms vary widely from patient to patient. cervical VEMPs are necessary to confirm the clinical sig- Precipitating factors for the vertigo or oscillopsia in- nificance of the radiology findings.10 clude loud noise, or activities that produce changes in the middle ear or ICP, such as lifting, straining, nose blowing, Examination and Provocative Testing Valsalva maneuvers, or pressure on the ear. Exercise and Signs of SSCD syndrome can be induced with tones at exertion-induced vestibular symptoms have been associ- escalating frequencies and intensities, compression of the ated with SSCD adjacent to the superior petrosal sinus in 52 to increase external auditory canal pressure, jugu- particular. Antecedent head trauma or barotrauma may lar venous compression, and Valsalva maneuvers. Verti- be elicited in the history. cal torsional eye movements produced by these stimuli and observed with the patient wearing Frenzel lenses are Diagnostic Evaluation pathognomonic for SSCD syndrome.26 Nystagmus or ves- Differential diagnoses that often mimic SSCD syn- tibular activation elicited by pressure changes at the ex- drome include eustachian tube dilatory dysfunction, ternal auditory canal, known as Hennebert’s sign, is also classically associated with canal dehiscence but is not patulous eustachian tube, , chronic otitis me- 39 dia, fistula, labyrinthitis, Ménière’s disease, diagnostic of it. Weber’s test typically lateralizes to the symptomatic ear; this is attributed to a conductive hearing migraine-associated vertigo, and vestibular schwannoma, 13 establishing it as a great otological mimicker.92 Accurate loss or intralabyrinthine hearing loss. diagnosis relies on consistent symptoms, signs, audiomet- ric and vestibular results, and imaging confirmation. In Audiometry Testing particular, HRCT is increasingly found to overestimate Hearing loss may be conductive, sensorineural, or the true incidence of the clinical syndrome, because the mixed. Bone conduction is decreased and air conduction presence of bony dehiscence alone does not necessarily is increased due to the presence of a mobile third window, indicate a pathological condition. Fortunately, the direc- thereby producing the air-bone gap. Normal symmetri- tion-specific physiology of semicircular canal biomechan- cal hearing helps eliminate retrocochlear pathologies as

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Unauthenticated | Downloaded 09/27/21 12:14 PM UTC Superior semicircular canal dehiscence a cause of vertigo. Furthermore, the stapedial (or acous- tic) reflex is typically preserved in SSCD, in contrast to other causes of hearing loss such as otosclerosis, where it is characteristically absent.59 Patients with predominantly vestibular rather than auditory symptoms may still exhibit some degree of hearing loss. Therefore, formal pure-tone audiometry is frequently useful to establish a baseline, es- pecially before planned operative interventions. After op- erative repair of SSCD, the air-bone gap may partially or completely resolve in long-term follow-up.43

Electrocochleography Testing Electrocochleography offers an alternative periopera- tive testing modality to assess SSCD pathological features FIG. 2. Temporal bone CT demonstrating illustrative case with (A) de- and repair. ECoG measurements reveal a significantly hiscence of the SSC (arrow) and tegmen (arrowheads) on the left, and with (B) intact middle cranial fossa floor on the right. Resurfacing of the higher cochlear summating potential/action potential ratio left middle fossa floor defects was performed with temporalis fascia and in affected by SSCD, with improvement observed fol- hydroxyapatite bone cement (C). lowing operative repair.1,7 The ECoG measurement is not specific to canal dehiscence because abnormal values are also observed in other inner-ear conditions such as Mé- techniques.32 An MRI study with a fast imaging employ- nière’s disease and perilymphatic fistula. Isolated observa- ing steady-state acquisition (FIESTA) sequence demon- tion of intraoperative ECoG has also noted normalization strates 100% sensitivity and negative predictive value, but of the summating potential/action potential ratio immedi- 96.5% specificity and 61% positive predictive value com- ately following canal occlusion. pared with CT in evaluating SSCD, suggesting that MRI might be adequate in excluding the diagnosis.15 Of note, Vestibular Evoked Myogenic Potential Testing near dehiscence with extremely thin bone can produce The VEMP assesses the response of postural muscles similar signs and symptoms as a fully dehiscent apical that are under tonic control of the medial vestibulospi- cap, and may benefit from operative intervention.86 Most nal tract to vestibular activation. Auditory stimuli, such importantly, imaging findings, as with all other diagnostic as loud clicks, usually induce relaxation of the ipsilateral adjuncts, should be interpreted against the background of sternocleidomastoid VEMP or orbicularis oculi VEMP, appropriate clinical symptoms and signs for a definitive which is measurable on electromyography. The pres- diagnosis of SSCD. ence of SSCD renders patients more sensitive to the au- ditory stimulus and produces a vestibulocollic response, Management in which the sternocleidomastoid muscle relaxes to ves- Management after clinical diagnosis begins with avoid- tibular stimulation, at a lower (< 65 dB) threshold than in 87 ance of provocative stimuli and vestibular sedation. It is control subjects on the affected side. Sternocleidomas- important to note that a majority of patients identified toid VEMP has 80%–96% sensitivity and specificity in with SSCD syndrome in the literature have not undergone confirming CT-proven SSCD, compared with > 90% for orbicularis oculi VEMP; both may provide an appropriate screening or confirmatory test in the diagnosis of SSCD syndrome.92,94 The VEMP can also distinguish between patients with near dehiscence, or thin bone, versus those with true dehiscence over the SSC, both of whom can present with similar symptoms.53 Following successful re- pair of the dehiscence, the VEMP normalizes.13,88

Imaging A thin-cut HRCT scan, particularly in the coronal plane, or an oblique cut directed to the plane of the semi- circular canal, is confirmatory of the clinical diagnosis (Fig. 2).9,12,49 However, even HRCT can produce false- positive results if the canal roof is thinner than the image resolution slice thickness, as might be expected given an average SSC roof thickness of 1 mm in cadaveric stud- ies.23,51,58,61,79 Osteoporosis can also lead to a false-positive FIG. 3. Reformatted CT images perpendicular (A, Stenver’s plane) or reading because of lack of calcium in the imaged bone. parallel (B, Pöschl’s plane) to the SSC may aid visualization of a bony Reformatted images parallel (Pöschl’s plane) or perpen- dehiscence (arrows). Lines superimposed on an axial temporal bone dicular (Stenver’s plane) to the SSC may aid visualization CT image indicate the plane of reconstruction for (C) Stenver and (D) of a dehiscence (Fig. 3),9,29 as do novel 3D reconstruction Pöschl views.

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Unauthenticated | Downloaded 09/27/21 12:14 PM UTC W. L. Bi et al. surgical repair. Operative intervention is indicated for in- reconstruction, and surgical corridor.6,27,80 Endoscopic as- tractable or debilitating symptoms. Surgical repair can be sistance provides another adjunct, based on surgeon pref- accomplished through resurfacing of the SSC roof, plug- erence.75 ging of the osseous defect, or reinforcement of the round Analysis of select cases of recurrent SSCD symptoms or oval window to diminish the third window effect (Fig. after use of an autologous temporal bone split-thickness 1C and D). calvarial bone graft to resurface the middle fossa has revealed resorption of the bone graft; this prompted the Canal Plugging conclusion that the entire temporal bone is abnormal in patients with SSCD and that resurfacing using a calvarial The original report of SSCD operative repair described 36 a middle fossa subtemporal extradural approach to ex- bone graft carries a higher risk of resorption. Concern pose the roof of the SSC and plug the defect with fascia,60 for graft resorption or migration as a mechanism of re- which has been subsequently expanded to muscle, bone surfacing failure over time prompts some surgeons to fa- 56,70 69 vor bone source substitute or silicone elastomer over au- wax, and bone pâté. Given the risk of false-positive 38 CT diagnoses, the middle fossa approach allows en face tologous grafts. Securing of the fascia-bone graft to the calvaria with a small plate has also been performed, with visualization and confirmation of the defect prior to op- 24 erative repair (either occlusion or resurfacing), and can be satisfactory results. Evolving appreciation of the biologi- further augmented by endoscopy in select cases.19 cal sequelae of reconstruction suggests that experience from earlier resurfacing series may not be comparable to As an alternative, transmastoid occlusion of the SSC contemporary results because of modifications to the tech- appeals to otologists due to their ability to access large nique. areas of dehiscence via a familiar approach, the ability to occlude the canal without manipulating the defect, and Round Window Reinforcement the relatively lower invasiveness of a mastoidectomy com- pared with a craniotomy.2,11,13,46,91 This can be achieved Several groups empirically investigated tissue graft with bone pâté or temporalis fascia placed within the reinforcement of the round window, having observed SSC, with > 90% postoperative improvement in vestibu- that patients who had undergone procedures to repair a lar and hearing symptoms.11 Some prefer the transmastoid presumed perilymph fistula prior to the initial report of approach for repair of medially located SSCD adjacent SSCD, in retrospect may have had SSCD and may have to the superior petrosal sinus.53,80 This surgical approach, experienced significant benefit. The mechanism for why however, offers more limited visualization of the dehis- it may help is uncertain, but it has been postulated that it cence and may be less favorable in the setting of a poorly may be influencing the impedance of the inner-ear system, perhaps reducing global hypercompliance and consequent pneumatized temporal bone, low-lying temporal fossa, or 67,76,77 extensive concurrent tegmen defects. Concurrent plugging compression-related endolymph displacement. The of the defect, along with reconstruction or resurfacing of round window is directly accessible through a tympanic the floor, is achievable through either a middle fossa or a membrane opening and can be reinforced with soft tis- transmastoid approach.31,35,37 sue such as fascia, perichondrium, or muscle, gently filling The choice of reconstructive material may also influ- the round window niche after excoriating the mucosa, but ence long-term outcome, although experience remains carefully preserving the membrane. Gelfoam or an autolo- limited. In an animal model of semicircular canal oc- gous blood patch placed through a myringotomy can be clusion, comparison of bone dust, bone wax, or muscle done as a trial in an office setting. All of these can also be revealed that the bone dust group had the best hearing removed in the event of symptom worsening. Over-stiffen- outcomes, with periosteal osteoneogenesis; the bone wax ing of the round window with bone wax or cartilage may divert additional acoustic energy into the dehiscence and group had the poorest hearing outcomes, with no osteo- cause a worsening of symptoms that can be reversed by neogenesis observed but with the presence of perilym- removal of the material.75 It appears that gentle reinforce- phatic inflammation.46 ment of the round window may be beneficial—for reasons to be determined—as opposed to severe dampening of the Canal Roof Resurfacing and Capping round window, which exacerbates the condition, as may be Reconstruction or resurfacing of the dehiscent middle predicted from the “third window” model.67,75 fossa floor with fascia, perichondrium, cartilage,6 split- There is a paucity of clinical data examining outcomes thickness cortical bone,59 bone substitute (e.g., hydroxy- following round window reinforcement for SSCD syn- apatite or calcium phosphate),50,68 synthetic elastomer,38 or drome. Postoperative improvement in the full gamut of a combination thereof, is a common alternative to canal SSCD-related symptoms has been reported, with the ex- plugging. The use of hydroxyapatite cement for reconsti- ception that conductive hearing loss does not improve.77 tuting the apical defect has also been termed capping.41,62 Although some advocate that round window occlusion Notably, resurfacing allows for reconstruction of multiple should be performed in patients whose primary symptom middle fossa floor defects, which is regularly encountered is conductive hyperacusis,67 others suggest that both oval in the setting of SSCD. and round window reinforcement may be beneficial for As with canal plugging, resurfacing can be accom- that symptom.75 plished via either a middle fossa or a transmastoid ap- A concern is that the clinical outcome following round proach, with their respective strengths and limitations in window reinforcement may not be as durable as superior terms of ease of visualization, available surface area for canal plugging or resurfacing techniques; symptoms may

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Unauthenticated | Downloaded 09/27/21 12:14 PM UTC Superior semicircular canal dehiscence recur as the obliterated tissue atrophies. The minimally in- cite a higher success rate with canal plugging compared vasive nature of this outpatient procedure, and its distinct with resurfacing,57 especially as a means to treat vestibular anatomical corridor compared with the middle fossa or imbalance; however, canal plugging demonstrates efficacy transmastoid approaches, allows for subsequent resurfac- equivalent to capping with hydroxyapatite, which is in es- ing or plugging if symptoms fail to improve. Alternatively, sence a reconstruction operation with nonmigratory mate- some practitioners use obliteration of the round window rial.84 In a meta-analysis, all operative modalities achieved in a diagnostic setting for patients with highly suspect equal success if auditory symptomatology was the pri- clinical findings, absent or equivocal CT evidence of de- mary indication for intervention. In addition to symptom hiscence, but lowered thresholds with cervical VEMP or resolution, improvements in the VEMP threshold and air- increased amplitude with ocular VEMP; clinical improve- bone conduction gap are frequently observed following ment may prompt subsequent transcranial repair or contin- successful repair of canal dehiscence. ued monitoring.77 Vestibular hypofunction3,58 and hearing loss60 are the most feared complications following SSCD repair. Im- Considerations in Bilateral SSCD pairment of the SSC function in isolation is common after In the setting of bilateral SSCD, operative intervention plugging.17 More global vestibular hypofunction is ob- should address the symptomatic or more severely symp- served in approximately one-third of patients in the early tomatic side first.54 The radiographic appearance of bi- postoperative period following middle fossa plugging, lateral SSCD is frequently detected and does not warrant with higher risk associated with an increased length of the intervention in the absence of symptoms. Repair of SSCD dehiscent area.3 This may result from intraoperative loss on one side can provoke or be followed by development or displacement of perilymph and redistribution of endo- of contralateral symptoms attributable to the second canal lymph into the horizontal and posterior canals by the plug dehiscence, and patients must be counseled appropriately.4 or during dural elevation over the dehiscent canal, during Subsequent plugging of the second side is associated with which extra caution should be exerted. These symptoms oscillopsia in half of the patients, but still provides satis- typically resolve over time as perioperative fluid resolves factory relief of the primary debilitating symptoms. Bilat- and physiological vestibular compensation is attained,43 eral canal dehiscence is also associated with a prolonged with 11% of patients demonstrating vestibular impairment course of symptom recovery following unilateral canal at 6 weeks postoperatively.3 Because of the concern for plugging, for which patients should be counseled.66 compromise of SSC function, some surgeons favor resur- facing over plugging strategies; capping with hydroxyapa- Considerations in Pediatric Patients tite may offer a suitable option of minimizing postopera- Experience with SSCD diagnosis and management in tive vestibular side effects while providing high rates of children remains limited,47,52,93 although imaging series relief from preoperative vestibular handicap. suggest a 3%–10% incidence.21,73 Children present with a Significant hearing loss is uncommon after SSCD re- varied constellation of hearing loss, vertigo, and disequi- pair, and does not correlate with either the plugging or re- librium, with auditory symptoms typically occurring first. surfacing technique.48 In comparison, mild high-frequen- Diagnosis of vestibular symptoms is more challenging in cy sensorineural hearing loss, without change in speech younger children, and may manifest as delayed onset of discrimination, has been observed in 25% of patients after walking.47 The radiographic appearance of SSCD in chil- canal plugging via a middle fossa approach.85 Early meth- dren younger than 3 years of age is consistent with normal ods emphasized full occlusion of the membranous supe- development, and should be handled with observation. rior canal during plugging, which might incur a higher Conservative treatment is favored in children, including risk of postoperative hearing loss.60 Use of bone pâté for the use of hearing aids, with operative intervention re- plugging may be associated with a lower risk of hearing served for intractable vestibular handicap. impairment compared with other occlusive materials.2,45 Not surprisingly, the incidence of hearing loss rises in re- Perioperative Considerations vision procedures for SSCD, presumably due to adhesions Perioperative steroids are given variably across reports, at the surgical site and injury to the often for longer durations if signs of sensorineural hearing while separating the dura. Prior surgery on the cochlea or loss, labyrinthine hypofunction, or facial paresis are de- stapes also increases the risk for hearing loss following tected postoperatively.66,85 Early postoperative persistence SSCD repair.48 or slight decline in auditory and vestibular function may Patients with bilateral SSCD, larger defects, and a his- be due to fluid, blood, or air at the surgical site, and may tory of migraines are more likely to experience a pro- be monitored. Preoperative and postoperative audiometry longed duration of symptoms following operative repair.66 and vestibular testing allow objective tracking of symp- dysfunction, CSF leakage, and other neu- toms and outcomes, especially as experience with this dis- rological morbidities are rare after SSCD repair. On the ease entity accrues. whole, quality of life measures and outcomes remain to be clarified for patients with SSCD. Outcomes The majority of patients report improvement in pre- Conclusions senting symptoms following operative repair of SSCD, Over the past 2 decades, SSCD has been increasing- regardless of the technique.6,11,25,37,41,57,62,66 Many studies ly recognized as a treatable cause of disequilibrium and

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Unauthenticated | Downloaded 09/27/21 12:14 PM UTC W. L. Bi et al. hearing loss. Its distinctive pathophysiology, arising from sponses of vestibular afferents in a model of superior canal the introduction of a mobile “third window” formed by dehiscence. Otol Neurotol 25:345–352, 2004 an unprotected membranous labyrinth at the apex of the 17. Carey JP, Migliaccio AA, Minor LB: Semicircular canal function before and after surgery for superior canal dehis- superior canal, accounts for characteristic symptoms, di- cence. Otol Neurotol 28:356–364, 2007 agnostic signs, and treatment options. Regardless of the 18. Carey JP, Minor LB, Nager GT: Dehiscence or thinning of approach, most patients experience alleviation of present- bone overlying the superior semicircular canal in a temporal ing symptoms following operative repair of the SSCD, al- bone survey. Arch Otolaryngol Head Neck Surg 126:137– though risk of vestibular hypofunction and hearing loss 147, 2000 remain avenues for future improvement. The choice of op- 19. Carter MS, Lookabaugh S, Lee DJ: Endoscopic-assisted re- erative strategy ultimately depends on the surgeon’s expe- pair of superior canal dehiscence syndrome. Laryngoscope rience and preference. A multidisciplinary approach to the 124:1464–1468, 2014 management of SSCD will continue to optimize outcomes 20. Cawthorne T: Chronic adhesive otitis. J Laryngol Otol 70:559–564, 1956 for this newly recognized disease entity. 21. Chen EY, Paladin A, Phillips G, Raske M, Vega L, Peterson D, et al: Semicircular canal dehiscence in the pediatric popu- References lation. Int J Pediatr Otorhinolaryngol 73:321–327, 2009 22. Chi FL, Ren DD, Dai CF: Variety of audiologic manifesta- 1. 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