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Superior semicircular canal dehiscence: Diagnosis and management
Journal of Clinical Neuroscience xxx (2017) xxx–xxx
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Journal of Clinical Neuroscience journal homepage: www.elsevier.com/locate/jocn
Review article
Superior semicircular canal dehiscence: Diagnosis and management Christine Mau a,c, Naveed Kamal c, Saiaditya Badeti c, Renuka Reddy b, Yu-Lan Mary Ying b, Robert W. Jyung b, James K. Liu b,c,⇑ a
Department of Neurological Surgery, Milton S. Hershey Penn State Medical Center, Hershey, PA, USA Department of Otolaryngology, Rutgers New Jersey Medical School, Newark, NJ, USA c Department of Neurological Surgery, Rutgers New Jersey Medical School, Newark, NJ, USA b
a r t i c l e
i n f o
Article history: Received 4 August 2017 Accepted 15 November 2017 Available online xxxx Keywords: Superior semicircular canal dehiscence SSCD Surgical techniques Neurosurgery Otolaryngology
a b s t r a c t The authors provide an update on the clinical manifestations, diagnosis and various approaches to the treatment of superior semicircular canal dehiscence (SSCD). SSCD is a rare condition where the bone overlying the superior semicircular canal thins or dehisces causing characteristic clinical findings. Since this was first reported in 1998 by Minor and colleagues, there has been much advancement made in terms of diagnosis and treatment. Signs and symptoms include a wide variation of both vestibular and auditory manifestations. Diagnosis made solely on clinical signs is difficult due to how varied the presentations can be and the overlap with other otologic pathologies. High-resolution CT temporal scans have been the standard in confirming superior semicircular canal dehiscence, however, MRI FIESTA scans have recently been used to image SSCD. Additionally, audiometry and vestibular evoked myogenic potential (VEMP) testing are useful screening tools. Currently, the middle fossa approach is the most common and standard surgical approach to repair SSCD. The transmastoid, endoscopic and transcanal or endaural approaches have also been recently utilized. Presently, there is no consensus as to the best approach, material or technique for repair of SSCD. As we learn more, newer and less invasive approaches and techniques are being used to treat SSCD. We present a comprehensive review of SSCD, including clinical symptoms and presentation, histopathology, diagnosis, treatment strategies and outcomes of intervention. Ó 2017 Elsevier Ltd. All rights reserved.
1. Introduction Superior semicircular canal dehiscence (SSCD) was first described by Minor and colleagues in 1998 as the cause for sound-induced vertigo (Tullio phenomenon) not otherwise explained by infectious causes [1]. Patients experienced either vertigo or oscillopsia after exposure to certain frequencies of sounds or maneuvers which induced pressure changes within the labyrinth. The diagnosis was made radiographically by computed tomography (CT) of the temporal bones and treatment involved plugging the dehiscent area. Dehiscence of the otic capsule overlying the superior semicircular canal leads to creation of a ‘‘mobile third window” of the innerear, with the first and second windows referring to the round and oval windows, respectively. When exposed to either high-intensity sounds or pressure changes such as in valsalva maneuvers, pressure changes occur across this third window. Theoretically, the ⇑ Corresponding author at: 90 Bergen Street, Suite 8100, PO Box 1709, Newark, NJ 07101-1709, USA. E-mail address: [email protected] (J.K. Liu).
pressure change generates a displacement of endolymph through positive or negative pressure in the external auditory canal towards the dehiscence in the arcuate eminence [2]. This endolymph displacement causes deflection of the cupula resulting in the wide array of symptoms associated with SSCD. The increased elasticity provided by the third window may lead to loss of acoustic energy, which would explain the manifestation of lowfrequency conductive hearing loss, but also provide a mechanism for improved cochlear bone conduction by lowering the impedence on the scala vestibuli side of the cochlea [2–5]. The prevalence of SSCD is not well-defined in the literature. There have been several studies to determine its prevalence, however, the diagnosis requires both clinical symptoms and highresolution CT temporal bone scans, which skew the population being examined. The literature reports a prevalence rate between 0.7 and 9.0% in non-pediatric populations [6–10]. In pediatric populations over 3 years of age, prevalence has been reported to be 10.7% [11]. Patients under 3 years of age are excluded from prevalence studies, because they have not fully formed the temporal bone overlying the superior semicircular canal. A recent publica-
https://doi.org/10.1016/j.jocn.2017.11.019 0967-5868/Ó 2017 Elsevier Ltd. All rights reserved.
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tion reported a correlation between patients with SSCD and higher body mass index, obstructive sleep apnea rates, and accompanying tegmen defects; suggesting a causal relationship between increased intracranial pressure and formation of SCCD [12].
2. Clinical symptoms and presentation The range of symptoms seen in SSCD patients are all manifestations of thinning or complete dehiscence of the bone overlying the superior semicircular canal which creates a ‘‘third window”. The clinical symptoms range from vertical-torsional nystagmus to autophony to bone-conduction hyperacusis (see Table 1). Vestibular manifestations include vertigo, nystagmus and oscillopsia provoked by loud sounds or pressure changes. Auditory manifestations include autophony for internally conducted sounds, bone-conduction hyperacusis on audiometry, pulsatile tinnitus, phonophobia, and aural fullness [1,13–16]. The acoustic vibrations transmitted to the oval window are partially absorbed by this third window manifesting in the distinct symptomatologies described above. Diagnosis is often challenging based on clinical presentation alone because SSCD patients have various vestibular and auditory symptoms that may mimic other otologic pathologies [13,17,18]. Because vertigo provoked by pressure changes can be associated with other entities where there is leakage of inner ear fluid (i.e. perilymphatic fistulae), it is suspected that numerous cases of SSCD have been mistaken for other conditions. Many patients exhibit a characteristic torsional eye movement upward and away from the affected ear. This nystagmus can be induced by sound (Tullio phenomenon) or pressure change (Hennebert’s sign) when the patient is straining, as during coughing. It occurs when sound or pressure waves are transmitted over the superior canal ampulla and through the dehiscence. This stimulates the superior canal ampulla causing the characteristic nystagmus. The direction of the nystagmus is due to the direction of
Table 1 Table of Symptoms. Symptoms of Superior Semicircular Canal Dehiscence [1,12,14–16] Category
Symptom
Description
Auditory
Autophony
Amplified heartbeat, amplified footstep, ability to hear eyeball movements Test: place vibrating force at medial malleolus of the ankle, patient will report being able to hear but not feel the tuning fork in the affected ear May be induced by the patients’ own voice
Boneconduction hyperacusis Pulsatile tinnitus Low frequency hearing loss
Vestibular
Phonophobia Aural fullness Tullio phenomenon Hennebert’s sign Oscillopsia
Vertigo Chronic disequilibrium
Low frequency sounds exit preferentially through the dehiscence and are lost unless at elevated thresholds Common and debilitating symptom of SSCD Common symptom, but oftentimes tolerable Characteristic torsional eye movement upward and away from the affected ear induced by sound Characteristic torsional eye movement upward and away from the affected ear induced by pressure changes Disturbance of the visual field where objects appear to oscillate; may be induced by loud sound or pressure changes May be induced by sound or pressure changes Thought to be related to persistent abnormal activation of vestibular receptors; most debilitating symptom
endolymph flow [15,17]. This nystagmus is specific to SSCD [15,16,19]. Another characteristic sign can be elicited using tuning fork testing. By placing a vibrating fork at the medial malleolus of the ankle, the patient will report being able to hear but not feel the tuning fork in the affected ear (bone-conduction hyperacusis). A majority of patients with SSCD are acutely sensitive to internally generated or conducted sounds in the affected ear (autophony). Classic examples of autophony are an amplified heartbeat, amplified footstep, and sometimes even being able to hear eyeball movements. The dehiscence acts as a low impedance window allowing the internally generated sounds to be directed into the labyrinth. Patients with SSCD can be exquisitely sensitive to changes in pressure of the affected ear. Patients often report finding relief from various symptoms by lying supine or sustaining a Valsalva maneuver [18]. During examination, use of the Valsalva maneuver can be exploited to illicit symptoms. The release of the Valsalva maneuver can cause a transient excitation of the superior ampulla due to a pressure change in the middle ear or the intracranial space, similar to dizziness evoked with pressure changes in the external auditory canal (Hennebert’s sign). 3. Histopathologic findings Infants uniformly have thin bone over the superior semicircular canals, which contributes to the hypothesis that dehiscence may result from failure of postnatal bone development [2]. Furthermore, the thin bone may contribute to a higher chance of dehiscence following trauma and precipitate SSCD. The roof of the superior semicircular canal is composed of layers of the otic capsule, which varies from 0.5 to 0.9 mm in thickness [20]. The erosion of bone is non-focal, and spans along the length of temporal bone overlying the superior semicircular canals. On histopathology, lamellae can be seen parallel to the surface of the superior petrosal sinus indicating that ossification is stable at one point [7]. This implies that the process leading to dehiscence could be a chronic, progressive condition. However, in 1000 specimens of temporal bones, there were no local bone changes, osteoporotic changes or underlying bone diseases found in any specimens to explain the thinning. Furthermore, the prevalence of otosclerosis is not significantly different in cases of SSCD [7]. 4. Diagnosis The diagnosis of SSCD can be elusive, requiring the clinician to consider all of the following: auditory and vestibular symptoms, audiogram and vestibular evoked myogenic potential (VEMP) testing results, and CT temporal bone scans findings. Although the diagnosis cannot be based on symptoms alone, the combination of autophony for internally-conducted sounds, hyperacusis, and imbalance or vertigo provoked with loud sounds or pressure changes should raise suspicion for SSCD [5]. Similarly, while a wide range of audiogram results can be found in SSCD cases, a lowfrequency conductive hearing loss with bone conduction hyperacusis, combined with preserved acoustic reflexes should prompt suspicion. Thus, the diagnosis of SSCD can be further elucidated by the use of audiometry testing. Conductive hearing loss can be measured by air-bone gaps, which is calculated by the difference between air and bone conduction thresholds on audiograms. The low frequency conductive hearing loss may be explained by the preferential loss of these frequencies through the dehiscence [3–5,17]. Sounds are only able to reach the cochlea at elevated thresholds. However, this low frequency hearing loss is not specific to SSCD and cannot be used as
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the only screening tool without reviewing high-resolution CT temporal bone scans. CT scans of the temporal bones are required to confirm SSCD. However, it is impractical to use as a screening measure for all patients who are suspected to have SSCD based solely on clinical presentation [18]. Vestibular evoked myogenic potential (VEMP) testing can be a very useful screening tool to evaluate SSCD, to differentiate between middle and inner ear pathologies [21]. A VEMP response is a measure of function of the inferior vestibular nerve [17]. There are two types of VEMP testing: cervical (cVEMP) and ocular (oVEMP). The cervical VEMP is an inhibitory electromyographic signal measured over the contracted sternocleidomastoid muscle ipsilateral to the ear being stimulated with sound; a consequence of saccular activation. Patients with SSCD have a lower than normal threshold for eliciting cVEMP responses (relaxation potential in the ipsilateral sternocleidomastoid muscle), and enlarged peak-to-peak amplitudes in the affected ear. This may be secondary to lower impedence of the vestibular system resulting in a lower resistance for pressure and sound transmission due to the dehiscent semicircular canal. Thus, cVEMP signals are enhanced in patients with SSCD. The ocular (oVEMP) is an excita-
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tory EMG response generated by the inferior oblique muscle contralateral to the stimulated ear; consequence of utricular activation. In patients with SSCD, oVEMPs also have lower thresholds and increased amplitudes, even to a greater extent than observed in cVEMP responses [22]. Air-conducted oVEMP responses appear to be more sensitive than cVEMP responses in diagnosing SSCD. VEMP testing can offer 91.4% sensitivity and 95.8% specificity; therefore, it is cost-effective and can serve as a practical screening method for SSCD before performing CT imaging [18]. High-resolution CT scans of the temporal bones are useful to confirm the diagnosis of SSCD due to its high sensitivity (Fig. 1) [20]. There is dispute over the accuracy of these scans due to their potentially high rate of false positives. In prevalence studies for SSCD, those assessed by using CT scans are higher by several folds than those assessed with cadaver studies [23,24]. Furthermore, the term ‘‘high-resolution” encompasses a wide span of parameters, including collimation, alignment of the scan and use of 3dimensional (3D) versus multi-planar CT reconstructions [25]. When examining data acquired from 1.0-mm, 0.55-mm and 0.5 mm collimated CT scans in the transverse and coronal planes, the
Fig. 1. High Resolution axial CT scan of the temporal bone, seen in the bone window. There is frank dehiscence (arrow) of at the anterior crus of the superior margin of the superior semicircular canal (A, B). Normal margins of the superior semicircular canal are shown for comparison (C, D).
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Table 2 Table of Treatment Options. Treatment Options for Superior Semicircular Canal Dehiscence [26–44] Approaches Approach
Description
Advantages
Disadvantages
Middle cranial fossa
4 4 craniotomy, temporal lobe retraction
Most invasive approach
Transmastoid
Standard mastoidectomy, visualization of lateral horizontal canal
Endoscopic
3 2 craniotomy, temporal lobe retraction
Transcanal/ Endaural
Reinforcement or occlusion of the round window
Direct visualization of the arcuate eminence and dehiscence; can use canal plugging, resurfacing or capping Less invasive than middle cranial fossa approach; may use canal plugging and modified resurfacing Less invasive than middle cranial fossa approach, less temporal lobe retraction, improved visualization of the dehiscence Can be performed in outpatient setting, eliminates need for ICU stay
No direct visualization of the dehiscence
Still requires temporal lobe retraction
Potentially decreased longevity of treatment
Techniques Technique
Description
Advantages
Disadvantages
Canal plugging
Drilling the dehiscence to open the canal further, then occluding it with bone wax, temporalis fascia, or plugging the lumen distal and proximal to the dehiscence Traditional technique involving resurfacing of the tegmen floor using fascia, bone and/or glue Modified resurfacing using hydroxyapatite bone cement to seal the dehiscence Use of fascia graft to reinforce the round or oval window through a transcanal or endaural approach
Provides relief of Tullio’s phenomenon, Hennebert’s sign and autophony within one month of surgery; may improve chronic dysequilibrium
Complications may include global vestibular hypofunction, poor improvement in boneconduction hyperacusis, oscillopsia; may cause high-frequency sensorineural hearing loss Significantly less effective than plugging or capping and has a high failure rate Less successful in treating hyperacusis; overall success comparable to canal plugging Fascia tends to atrophy and leads to failure as early as 6 months after treatment
Canal surfacing Canal capping Reinforcement of the round or oval window
High success rate in treating Tullio’s phenomenon and autophony Least invasive and can be done in an outpatient setting
positive predictive value (PPV) overall is 67% [20,26]. The PPV of 3D surface reconstructions is 68%, whereas the PPV of multi-planar reconstructions is 87% [25]. In comparison, the PPV of a lowthreshold VEMP response, conductive hearing loss and toneevoked nystagmus is 84%, 95% and 100%, respectively when examined individually [25]. There are shortcomings to relying on high-resolution CT scans. Aside from the potential inaccuracy of the scans, even with evolving technology by increasing the resolution, the amount of radiation exposure to patients may outweigh the benefits. While there have been publications highlighting the role of magnetic resonance imaging (MRI) in evaluating SSCD, specifically in analysis of fast imaging employing steady state acquisition (FIESTA) sequence, CT scan is still the gold standard and mandatory to confirm dehiscence in cases in which it is suspected on FIESTA imaging, due to false positive cases and subsequent low positive predictive value [27]. High-resolution CT scans reformatted in the planes of Stenver and Poschl are still needed to detect thin and dehiscent SSCD in some cases. Digital volume tomography (DVT) is currently used for dental procedures. The amount of radiation exposure is only 1% of that with spiral CTs and the resolution is comparable or better than highresolution CT and the total examination time is greatly shortened [24]. DVT is already used for high-resolution dental procedures, but its application for neuro-otologic pathologies has not been greatly explored. 5. Treatment strategies There are various approaches and techniques to surgically manage SSCD (Table 2). A review of the literature (see Table 3) currently shows four surgical approaches, which have demonstrated varying degrees of success: middle fossa, transmastoid, endoscopic, and transcanal or endaural. The surgical techniques used to repair the SSCD include canal plugging, canal resurfac-
ing, canal capping, and reinforcement of the round or oval window. The middle fossa approach involves a standard low temporal craniotomy, extradural temporal lobe retraction, and direct subtemporal exposure of the bony middle fossa floor to identify the arcuate eminence and SCCD [28]. Advantages of the middle fossa approach include the ability to directly visualize the dehiscence, and the ability to use various techniques to repair the dehiscence: canal plugging, resurfacing, and capping. Possible complications are facial paralysis, CSF leakage, temporal lobe edema, delayed onset seizures and intracranial bleeding [28]. Although the middle fossa approach is the traditional approach and is used most often, it is also the most invasive since it requires a craniotomy with some degree of temporal lobe retraction. However, recently a minimally invasive middle fossa keyhole craniectomy approach has been developed that offers an alternative to the standard approach with added benefits including a shorter operative time, a potential decrease in complication rate due to the smaller incision size, reduced postoperative pain and discomfort, and improved wound healing [29]. Alternatively, the transmastoid approach, first reported in North America in 2008, has been used as a less invasive approach as it avoids having to perform a craniotomy and can be performed under local anesthesia [30]. The transmastoid approach has been used with both canal plugging and modified resurfacing techniques. It involves a standard mastoidectomy that provides visualization of the superior semicircular canal. However, unlike the middle fossa approach, the transmastoid approach does not achieve direct visualization of the dehiscence over the semicircular canal [28,30–32]. More recently, endoscopic approaches have been described to perform plugging and resurfacing. The endoscopic approach utilizes a smaller keyhole craniotomy (approximately 3 2 cm), requires less retraction of the temporal lobe, and provides improved visualization of the dehiscence [28,33].
Please cite this article in press as: Mau C et al. Superior semicircular canal dehiscence: Diagnosis and management. J Clin Neurosci (2017), https://doi.org/ 10.1016/j.jocn.2017.11.019
Study
No. Patients (No. ears)
Approach
Technique
Material
Results
Amoodi et al. (2011) [37] Beyea et al. (2012) [32]
4 (5)
Transmastoid
Resurfacing
16 patients (Includes 3 from Agrawal et al. (2008) [30]) 19 with follow-up
Transmastoid
Plugging
Silastic with bone pâté or fascia Bone pâté
Postoperatively all patients experienced disequilibrium which resolved in all but 1 (bone pâté) 15 with complete resolution, 1 with vestibular symptoms not improved. 2 with small dural tears that were repaired
Middle fossa
Carter et al. (2014) [33] Crane et al. (2010) [38] Friedland et al. (2006) [45] Hahn et al. (2010) [50]
5 19 (19) 2
Endoscopic Middle fossa Middle fossa
Plugging (18), Resurfacing (1) Plugging Plugging Resurfacing
Fascia and bone graft (plugging and resurfacing) Fascia graft Fascia graft Fascia graft
2 patients (11%) with global vestibular hypofunction, all exhibited superior canal hypofunction All reported improvement in symptoms. 14 with complete resolution of autophony, 2 decreased to mild symptoms. Study specifically examined 2 patients with return of symptoms due to bone resorption
3
Middle fossa
Resurfacing
Hillman et al. (2006) [46] Janky et al. (2012) [40]
13 (16)
Middle fossa
Capping
All 3 with complete resolution of symptoms except for 1 with only partial resolution of hearing loss. 1 with continued vestibular symptoms and 1 with hearing loss.
20
Middle fossa
Plugging and resurfacing
Silastic with bone pâté or fascia Fascia graft and hydroxyapatite bone cement Fascia and bone pâté
Limb et al. (2006) [41]
19 without previous surgery, 10 with previous surgery 11 (11)
Middle fossa
Plugging and/or resurfacing
Fascia and bone graft
Middle fossa
Plugging (10) and resurfacing (1)
Bone Wax
5 (6)
Middle fossa
Fascia and bone pâté
1 (1)
Transcanal
Plugging (5) and resurfacing (1) Round window occlusion
19
Transcanal
5 (5) 40 (43) 10 (11)
Carey et al. (2007) [36]
Mikulec et al. (2005) [39] Phillips et al. (2010) [43] Silverstein et al. (2009) [34] Silverstein et al. (2014) [35] Teixido et al. (2011) [51] Ward et al. (2012) [42] Zhao et al. (2012) [31]
Transmastoid
Round window reinforcement – delicate coverage (19) Resurfacing
Cartilage, bone wax, perichondrium Fascia, cartilage, perichondrium, adipose, gelfoam and/or silastic Fascia and bone pâté
Middle fossa Transmastoid
Plugging Plugging
Fascia and bone graft Fascia and bone pâté
Spontaneous nystagmus (6/10 patients) and post head-shaking nystagmus (8/10 patients). 10/10 patients with positive head impulse test. Immediately post-op, increased fall risk. Patients with previous stapes procedure (1) and semicircular repair (2) had postoperative hearing loss. 2 of 6 surgery naïve patients with preoperative hearing loss had further hearing loss. 1 with mild hearing loss, 2 with both mild hearing loss and vestibular hypofunction. 10 (plugging) with significant reduction or complete resolution of symptoms. 1 unsuccessful (resurfacing) 1 with moderate vertigo, 2 with minimal vertigo. Transient hearing loss in 3 patients (1 resurfacing, 2 plugging) Complete resolution of symptoms Improvement in 8 symptoms, but worsened hearing loss
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No hearing loss. 1 with mild disequilibrium treated with tympanostomy tube Mild hearing loss in 25% of patients Hearing preservation in all patients, minor imbalance and tinnitus in 6 patients. Vertigo and phonophobia in 1 patient
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Please cite this article in press as: Mau C et al. Superior semicircular canal dehiscence: Diagnosis and management. J Clin Neurosci (2017), https://doi.org/ 10.1016/j.jocn.2017.11.019
Table 3 Surgical repair technique and approach used to treat Superior Semicircular Canal Dehiscence.
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Another minimally invasive approach is occlusion of the round window through a transcanal or endaural approach [28,34,35]. This economical approach can be performed in an outpatient same-day surgery setting, decreased anesthesia time (either general anesthesia or local with intravenous sedation), and eliminated need for ICU stay [35]. Identifying the round window membrane and reinforcing it by overlying with another material, the idea is to occlude the round window and eliminate a ‘‘third window” effect. In practice, this approach eliminated Tullio’s phenomenon and autophony [28,34,35]. Additionally, the approach achieved the same level of symptom improvement as studies that utilized other approaches [49]. Different materials have been tried including fascia and cartilage grafts, bone wax and perichondrium for reinforcement. The use of a fascia graft only as the occluding material may decrease the longevity of this treatment because it has been reported to fail as early as 6 months after treatment [28]. The three repair techniques: resurfacing, capping and plugging, are all designed to eliminate the third window, thus eliminating the symptoms of SSCD. Initially, treatment involved resurfacing the tegmen floor using fascia, bone graft, and glue through a middle fossa approach [1]. However, it was later discovered that in reality there was occlusion of the SSC in these patients [36]. Strictly, canal resurfacing involves the use of bone graft or cartilage to cover the dehiscence without occluding the canal. Capping is a modification to the resurfacing technique which uses hydroxyapatite bone cement to seal the dehiscence. Resurfacing and capping seal off communication between the labyrinth and the brain [37]. Plugging involves drilling the dehiscence to open the canal further and then occluding it using either bone wax or temporalis fascia or plugging the superior SSC lumen distal and proximal to the dehiscence. When comparing the three techniques, the resurfacing method of management is significantly less effective than both plugging and capping [34]. Using the middle fossa approach, the three aforementioned techniques can be utilized. However, plugging is most often reported in the literature, (Table 2). Plugging provides relief of Tullio’s phenomenon, Hennebert’s sign, and autophony within one month after surgery [38]. It also may improve chronic disequilibrium, which is the most debilitating, although not a universal symptom of SSCD [39]. However, other studies suggest complications associated with plugging including global vestibular hypofunction, no improvement in bone-conduction hyperacusis, and
deficits in vestibule-ocular reflex function [34,36,39–41]. Some studies have also suggested a higher risk of mild high-frequency sensorineural hearing loss with plugging, secondary to the manipulation of the membranous labyrinth and possible damage to the cochlea from insertion of the plugging materials [37,42]. However, the latter cause was only found in patients who underwent previous procedures involving the cochlea or labyrinth [41,43]. Resurfacing through the middle cranial fossa approach is generally unsuccessful and has a higher failure rate [44,45]. Resurfacing typically uses a combination of fascia and bone graft. The fascia has been shown to atrophy and the bone graft can be resorbed or migrate, resulting in relapse of SSCD symptoms months after treatment. Half of patients treated with resurfacing have relapse of symptoms [44]. Canal capping using hydroxyapatite has a high success rate in resolving preoperative symptoms of Tullio phenomenon and autophony (Fig. 2). However, it is less successful in resolving hyperacusis [2]. Nevertheless, it has an overall success rate that is comparable to that of plugging [2,44,46]. Recent investigation of SSCD repair techniques in cadavers have suggested that a combination of plugging and capping is superior to plugging alone [47]. The transmastoid approach can be used to perform plugging and modified resurfacing techniques [48]. As discussed above, plugging is successful in relieving autophony, Tullio’s phenomenon, hyperacusis, positional vertigo, and generally has good preservation of hearing [31,32]. Additionally, the transmastoid approach combined with resurfacing has been shown to be the best surgical treatment to treat ear fullness [48]. However, there is an increased chance of postoperative imbalance and tinnitus, and sometimes mild sensorineural hearing loss [28,31,32]. Also, while no significant difference has been shown between the transmastoid approach and the middle fossa approach, a difference in admission length, adverse events, and total follow-up time is observed with the transmastoid approach being the safer alternative to the middle fossa approach. However, this can be due to the fact that more patients are treated with the middle fossa approach with plugging and are subjected to a higher complication risk associated with intracranial procedures. In an effort to reduce the risk of craniotomy-related complications, a growing number of studies implement the transmastoid approach combined with the plugging technique to rectify the dehiscence [48,49].
Fig. 2. Intraoperative imaging of the SSCD from the middle fossa approach. (A) The SSCD can be seen via the middle fossa approach. The temporal lobe is retracted superiorly extradurally to expose the superior semicircular canal. The greater superficial petrosal nerve (GSPN) is seen in this exposure. (B) Capping with hydroxyapatite bone cement is utilized to repair the SSCD defect.
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Another technique that has been reported is the modified resurfacing [38,48]. Although resurfacing has been relatively unsuccessful previously due to atrophy and resorption of the fascia and bone grafts, modified resurfacing uses a small silicone elastomer (Silastic) sheeting material between the dura and the dehiscence to reinforce either bone pâté or fascia. In the reported cases of modified resurfacing technique using silastic, all patients experienced nearly complete resolution of preoperative symptoms and had preservation of hearing [37,50]. Since silastic material is used, there is a lower risk of resorption. Modified resurfacing has also been performed using a soft tissue graft of tragal perichondrium [51]. Overall, patients reported a lower mean number (i.e., 5.4) of symptoms and signs postoperatively when compared to a higher mean number (i.e., 12.2) of symptoms and signs preoperatively [51]. Hearing abilities were preserved in all patients [51]. There have been two reports of endoscopic middle fossa approaches to repair SSCD [28,33]. One report used a 0-degree endoscope and attempted resurfacing using hydroxyapatite bone cement. The authors used a 2-cm circular craniotomy to access the dehiscence and required less retraction of the temporal lobe. They reported a greater than 93% success rate in eliminating preoperative symptoms [28]. The other report used a 30-degree endoscope and a 3 2 cm craniotomy [33]. The endoscopes allowed for direct visualization of the defect in the arcuate eminence. The authors used bone wax to plug the superior semicircular canal in this study. All the patients reported improvement of their preoperative symptoms. Of the patients tested, hearing was preserved when compared to preoperative audiometry testing. In a recent systematic review assessing the surgical repair techniques for SSCD repair found that there was no significant difference between the plugging, capping, resurfacing, and plugging with resurfacing [52]. There were also no significant differences in outcome between the middle fossa and transmastoid approaches. Thus, surgical treatment for the patients experiencing severe symptoms of SSCD is safe and feasible. 6. Conclusion Superior Semicircular Canal Dehiscence (SSCD) is still a relatively new pathologic condition that requires a high clinical suspicion for its correct diagnosis. Varied symptoms and presentations highlight the importance of other diagnostic tools including audiovestibular testing and imaging studies that are necessary for proper diagnosis of SSCD. While different surgical approaches and techniques have been published in the literature, with the middle fossa approach as the standard and most familiar approach for both neurosurgeons and otolaryngologists, more investigation is needed to determine the outcomes and efficacy of treatment with other more recently described techniques. Newer modifications to the middle fossa approach suggest added benefits related to reduced complication rates and operative time. As we learn more about that pathophysiology of SCCD, more precise diagnostic tools and surgical strategies will be available to properly diagnose and treat this elusive medical condition. Conflict of interest and source of funding The authors have no personal, financial, consultant or institutional interest in any of the drugs, material, or devices described in this article. Appendix A. Supplementary data Supplementary data associated with this article can be found, in the online version, at https://doi.org/10.1016/j.jocn.2017.11.019.
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Review article
Superior semicircular canal dehiscence: Diagnosis and management Christine Mau a,c, Naveed Kamal c, Saiaditya Badeti c, Renuka Reddy b, Yu-Lan Mary Ying b, Robert W. Jyung b, James K. Liu b,c,⇑ a
Department of Neurological Surgery, Milton S. Hershey Penn State Medical Center, Hershey, PA, USA Department of Otolaryngology, Rutgers New Jersey Medical School, Newark, NJ, USA c Department of Neurological Surgery, Rutgers New Jersey Medical School, Newark, NJ, USA b
a r t i c l e
i n f o
Article history: Received 4 August 2017 Accepted 15 November 2017 Available online xxxx Keywords: Superior semicircular canal dehiscence SSCD Surgical techniques Neurosurgery Otolaryngology
a b s t r a c t The authors provide an update on the clinical manifestations, diagnosis and various approaches to the treatment of superior semicircular canal dehiscence (SSCD). SSCD is a rare condition where the bone overlying the superior semicircular canal thins or dehisces causing characteristic clinical findings. Since this was first reported in 1998 by Minor and colleagues, there has been much advancement made in terms of diagnosis and treatment. Signs and symptoms include a wide variation of both vestibular and auditory manifestations. Diagnosis made solely on clinical signs is difficult due to how varied the presentations can be and the overlap with other otologic pathologies. High-resolution CT temporal scans have been the standard in confirming superior semicircular canal dehiscence, however, MRI FIESTA scans have recently been used to image SSCD. Additionally, audiometry and vestibular evoked myogenic potential (VEMP) testing are useful screening tools. Currently, the middle fossa approach is the most common and standard surgical approach to repair SSCD. The transmastoid, endoscopic and transcanal or endaural approaches have also been recently utilized. Presently, there is no consensus as to the best approach, material or technique for repair of SSCD. As we learn more, newer and less invasive approaches and techniques are being used to treat SSCD. We present a comprehensive review of SSCD, including clinical symptoms and presentation, histopathology, diagnosis, treatment strategies and outcomes of intervention. Ó 2017 Elsevier Ltd. All rights reserved.
1. Introduction Superior semicircular canal dehiscence (SSCD) was first described by Minor and colleagues in 1998 as the cause for sound-induced vertigo (Tullio phenomenon) not otherwise explained by infectious causes [1]. Patients experienced either vertigo or oscillopsia after exposure to certain frequencies of sounds or maneuvers which induced pressure changes within the labyrinth. The diagnosis was made radiographically by computed tomography (CT) of the temporal bones and treatment involved plugging the dehiscent area. Dehiscence of the otic capsule overlying the superior semicircular canal leads to creation of a ‘‘mobile third window” of the innerear, with the first and second windows referring to the round and oval windows, respectively. When exposed to either high-intensity sounds or pressure changes such as in valsalva maneuvers, pressure changes occur across this third window. Theoretically, the ⇑ Corresponding author at: 90 Bergen Street, Suite 8100, PO Box 1709, Newark, NJ 07101-1709, USA. E-mail address: [email protected] (J.K. Liu).
pressure change generates a displacement of endolymph through positive or negative pressure in the external auditory canal towards the dehiscence in the arcuate eminence [2]. This endolymph displacement causes deflection of the cupula resulting in the wide array of symptoms associated with SSCD. The increased elasticity provided by the third window may lead to loss of acoustic energy, which would explain the manifestation of lowfrequency conductive hearing loss, but also provide a mechanism for improved cochlear bone conduction by lowering the impedence on the scala vestibuli side of the cochlea [2–5]. The prevalence of SSCD is not well-defined in the literature. There have been several studies to determine its prevalence, however, the diagnosis requires both clinical symptoms and highresolution CT temporal bone scans, which skew the population being examined. The literature reports a prevalence rate between 0.7 and 9.0% in non-pediatric populations [6–10]. In pediatric populations over 3 years of age, prevalence has been reported to be 10.7% [11]. Patients under 3 years of age are excluded from prevalence studies, because they have not fully formed the temporal bone overlying the superior semicircular canal. A recent publica-
https://doi.org/10.1016/j.jocn.2017.11.019 0967-5868/Ó 2017 Elsevier Ltd. All rights reserved.
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tion reported a correlation between patients with SSCD and higher body mass index, obstructive sleep apnea rates, and accompanying tegmen defects; suggesting a causal relationship between increased intracranial pressure and formation of SCCD [12].
2. Clinical symptoms and presentation The range of symptoms seen in SSCD patients are all manifestations of thinning or complete dehiscence of the bone overlying the superior semicircular canal which creates a ‘‘third window”. The clinical symptoms range from vertical-torsional nystagmus to autophony to bone-conduction hyperacusis (see Table 1). Vestibular manifestations include vertigo, nystagmus and oscillopsia provoked by loud sounds or pressure changes. Auditory manifestations include autophony for internally conducted sounds, bone-conduction hyperacusis on audiometry, pulsatile tinnitus, phonophobia, and aural fullness [1,13–16]. The acoustic vibrations transmitted to the oval window are partially absorbed by this third window manifesting in the distinct symptomatologies described above. Diagnosis is often challenging based on clinical presentation alone because SSCD patients have various vestibular and auditory symptoms that may mimic other otologic pathologies [13,17,18]. Because vertigo provoked by pressure changes can be associated with other entities where there is leakage of inner ear fluid (i.e. perilymphatic fistulae), it is suspected that numerous cases of SSCD have been mistaken for other conditions. Many patients exhibit a characteristic torsional eye movement upward and away from the affected ear. This nystagmus can be induced by sound (Tullio phenomenon) or pressure change (Hennebert’s sign) when the patient is straining, as during coughing. It occurs when sound or pressure waves are transmitted over the superior canal ampulla and through the dehiscence. This stimulates the superior canal ampulla causing the characteristic nystagmus. The direction of the nystagmus is due to the direction of
Table 1 Table of Symptoms. Symptoms of Superior Semicircular Canal Dehiscence [1,12,14–16] Category
Symptom
Description
Auditory
Autophony
Amplified heartbeat, amplified footstep, ability to hear eyeball movements Test: place vibrating force at medial malleolus of the ankle, patient will report being able to hear but not feel the tuning fork in the affected ear May be induced by the patients’ own voice
Boneconduction hyperacusis Pulsatile tinnitus Low frequency hearing loss
Vestibular
Phonophobia Aural fullness Tullio phenomenon Hennebert’s sign Oscillopsia
Vertigo Chronic disequilibrium
Low frequency sounds exit preferentially through the dehiscence and are lost unless at elevated thresholds Common and debilitating symptom of SSCD Common symptom, but oftentimes tolerable Characteristic torsional eye movement upward and away from the affected ear induced by sound Characteristic torsional eye movement upward and away from the affected ear induced by pressure changes Disturbance of the visual field where objects appear to oscillate; may be induced by loud sound or pressure changes May be induced by sound or pressure changes Thought to be related to persistent abnormal activation of vestibular receptors; most debilitating symptom
endolymph flow [15,17]. This nystagmus is specific to SSCD [15,16,19]. Another characteristic sign can be elicited using tuning fork testing. By placing a vibrating fork at the medial malleolus of the ankle, the patient will report being able to hear but not feel the tuning fork in the affected ear (bone-conduction hyperacusis). A majority of patients with SSCD are acutely sensitive to internally generated or conducted sounds in the affected ear (autophony). Classic examples of autophony are an amplified heartbeat, amplified footstep, and sometimes even being able to hear eyeball movements. The dehiscence acts as a low impedance window allowing the internally generated sounds to be directed into the labyrinth. Patients with SSCD can be exquisitely sensitive to changes in pressure of the affected ear. Patients often report finding relief from various symptoms by lying supine or sustaining a Valsalva maneuver [18]. During examination, use of the Valsalva maneuver can be exploited to illicit symptoms. The release of the Valsalva maneuver can cause a transient excitation of the superior ampulla due to a pressure change in the middle ear or the intracranial space, similar to dizziness evoked with pressure changes in the external auditory canal (Hennebert’s sign). 3. Histopathologic findings Infants uniformly have thin bone over the superior semicircular canals, which contributes to the hypothesis that dehiscence may result from failure of postnatal bone development [2]. Furthermore, the thin bone may contribute to a higher chance of dehiscence following trauma and precipitate SSCD. The roof of the superior semicircular canal is composed of layers of the otic capsule, which varies from 0.5 to 0.9 mm in thickness [20]. The erosion of bone is non-focal, and spans along the length of temporal bone overlying the superior semicircular canals. On histopathology, lamellae can be seen parallel to the surface of the superior petrosal sinus indicating that ossification is stable at one point [7]. This implies that the process leading to dehiscence could be a chronic, progressive condition. However, in 1000 specimens of temporal bones, there were no local bone changes, osteoporotic changes or underlying bone diseases found in any specimens to explain the thinning. Furthermore, the prevalence of otosclerosis is not significantly different in cases of SSCD [7]. 4. Diagnosis The diagnosis of SSCD can be elusive, requiring the clinician to consider all of the following: auditory and vestibular symptoms, audiogram and vestibular evoked myogenic potential (VEMP) testing results, and CT temporal bone scans findings. Although the diagnosis cannot be based on symptoms alone, the combination of autophony for internally-conducted sounds, hyperacusis, and imbalance or vertigo provoked with loud sounds or pressure changes should raise suspicion for SSCD [5]. Similarly, while a wide range of audiogram results can be found in SSCD cases, a lowfrequency conductive hearing loss with bone conduction hyperacusis, combined with preserved acoustic reflexes should prompt suspicion. Thus, the diagnosis of SSCD can be further elucidated by the use of audiometry testing. Conductive hearing loss can be measured by air-bone gaps, which is calculated by the difference between air and bone conduction thresholds on audiograms. The low frequency conductive hearing loss may be explained by the preferential loss of these frequencies through the dehiscence [3–5,17]. Sounds are only able to reach the cochlea at elevated thresholds. However, this low frequency hearing loss is not specific to SSCD and cannot be used as
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the only screening tool without reviewing high-resolution CT temporal bone scans. CT scans of the temporal bones are required to confirm SSCD. However, it is impractical to use as a screening measure for all patients who are suspected to have SSCD based solely on clinical presentation [18]. Vestibular evoked myogenic potential (VEMP) testing can be a very useful screening tool to evaluate SSCD, to differentiate between middle and inner ear pathologies [21]. A VEMP response is a measure of function of the inferior vestibular nerve [17]. There are two types of VEMP testing: cervical (cVEMP) and ocular (oVEMP). The cervical VEMP is an inhibitory electromyographic signal measured over the contracted sternocleidomastoid muscle ipsilateral to the ear being stimulated with sound; a consequence of saccular activation. Patients with SSCD have a lower than normal threshold for eliciting cVEMP responses (relaxation potential in the ipsilateral sternocleidomastoid muscle), and enlarged peak-to-peak amplitudes in the affected ear. This may be secondary to lower impedence of the vestibular system resulting in a lower resistance for pressure and sound transmission due to the dehiscent semicircular canal. Thus, cVEMP signals are enhanced in patients with SSCD. The ocular (oVEMP) is an excita-
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tory EMG response generated by the inferior oblique muscle contralateral to the stimulated ear; consequence of utricular activation. In patients with SSCD, oVEMPs also have lower thresholds and increased amplitudes, even to a greater extent than observed in cVEMP responses [22]. Air-conducted oVEMP responses appear to be more sensitive than cVEMP responses in diagnosing SSCD. VEMP testing can offer 91.4% sensitivity and 95.8% specificity; therefore, it is cost-effective and can serve as a practical screening method for SSCD before performing CT imaging [18]. High-resolution CT scans of the temporal bones are useful to confirm the diagnosis of SSCD due to its high sensitivity (Fig. 1) [20]. There is dispute over the accuracy of these scans due to their potentially high rate of false positives. In prevalence studies for SSCD, those assessed by using CT scans are higher by several folds than those assessed with cadaver studies [23,24]. Furthermore, the term ‘‘high-resolution” encompasses a wide span of parameters, including collimation, alignment of the scan and use of 3dimensional (3D) versus multi-planar CT reconstructions [25]. When examining data acquired from 1.0-mm, 0.55-mm and 0.5 mm collimated CT scans in the transverse and coronal planes, the
Fig. 1. High Resolution axial CT scan of the temporal bone, seen in the bone window. There is frank dehiscence (arrow) of at the anterior crus of the superior margin of the superior semicircular canal (A, B). Normal margins of the superior semicircular canal are shown for comparison (C, D).
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Table 2 Table of Treatment Options. Treatment Options for Superior Semicircular Canal Dehiscence [26–44] Approaches Approach
Description
Advantages
Disadvantages
Middle cranial fossa
4 4 craniotomy, temporal lobe retraction
Most invasive approach
Transmastoid
Standard mastoidectomy, visualization of lateral horizontal canal
Endoscopic
3 2 craniotomy, temporal lobe retraction
Transcanal/ Endaural
Reinforcement or occlusion of the round window
Direct visualization of the arcuate eminence and dehiscence; can use canal plugging, resurfacing or capping Less invasive than middle cranial fossa approach; may use canal plugging and modified resurfacing Less invasive than middle cranial fossa approach, less temporal lobe retraction, improved visualization of the dehiscence Can be performed in outpatient setting, eliminates need for ICU stay
No direct visualization of the dehiscence
Still requires temporal lobe retraction
Potentially decreased longevity of treatment
Techniques Technique
Description
Advantages
Disadvantages
Canal plugging
Drilling the dehiscence to open the canal further, then occluding it with bone wax, temporalis fascia, or plugging the lumen distal and proximal to the dehiscence Traditional technique involving resurfacing of the tegmen floor using fascia, bone and/or glue Modified resurfacing using hydroxyapatite bone cement to seal the dehiscence Use of fascia graft to reinforce the round or oval window through a transcanal or endaural approach
Provides relief of Tullio’s phenomenon, Hennebert’s sign and autophony within one month of surgery; may improve chronic dysequilibrium
Complications may include global vestibular hypofunction, poor improvement in boneconduction hyperacusis, oscillopsia; may cause high-frequency sensorineural hearing loss Significantly less effective than plugging or capping and has a high failure rate Less successful in treating hyperacusis; overall success comparable to canal plugging Fascia tends to atrophy and leads to failure as early as 6 months after treatment
Canal surfacing Canal capping Reinforcement of the round or oval window
High success rate in treating Tullio’s phenomenon and autophony Least invasive and can be done in an outpatient setting
positive predictive value (PPV) overall is 67% [20,26]. The PPV of 3D surface reconstructions is 68%, whereas the PPV of multi-planar reconstructions is 87% [25]. In comparison, the PPV of a lowthreshold VEMP response, conductive hearing loss and toneevoked nystagmus is 84%, 95% and 100%, respectively when examined individually [25]. There are shortcomings to relying on high-resolution CT scans. Aside from the potential inaccuracy of the scans, even with evolving technology by increasing the resolution, the amount of radiation exposure to patients may outweigh the benefits. While there have been publications highlighting the role of magnetic resonance imaging (MRI) in evaluating SSCD, specifically in analysis of fast imaging employing steady state acquisition (FIESTA) sequence, CT scan is still the gold standard and mandatory to confirm dehiscence in cases in which it is suspected on FIESTA imaging, due to false positive cases and subsequent low positive predictive value [27]. High-resolution CT scans reformatted in the planes of Stenver and Poschl are still needed to detect thin and dehiscent SSCD in some cases. Digital volume tomography (DVT) is currently used for dental procedures. The amount of radiation exposure is only 1% of that with spiral CTs and the resolution is comparable or better than highresolution CT and the total examination time is greatly shortened [24]. DVT is already used for high-resolution dental procedures, but its application for neuro-otologic pathologies has not been greatly explored. 5. Treatment strategies There are various approaches and techniques to surgically manage SSCD (Table 2). A review of the literature (see Table 3) currently shows four surgical approaches, which have demonstrated varying degrees of success: middle fossa, transmastoid, endoscopic, and transcanal or endaural. The surgical techniques used to repair the SSCD include canal plugging, canal resurfac-
ing, canal capping, and reinforcement of the round or oval window. The middle fossa approach involves a standard low temporal craniotomy, extradural temporal lobe retraction, and direct subtemporal exposure of the bony middle fossa floor to identify the arcuate eminence and SCCD [28]. Advantages of the middle fossa approach include the ability to directly visualize the dehiscence, and the ability to use various techniques to repair the dehiscence: canal plugging, resurfacing, and capping. Possible complications are facial paralysis, CSF leakage, temporal lobe edema, delayed onset seizures and intracranial bleeding [28]. Although the middle fossa approach is the traditional approach and is used most often, it is also the most invasive since it requires a craniotomy with some degree of temporal lobe retraction. However, recently a minimally invasive middle fossa keyhole craniectomy approach has been developed that offers an alternative to the standard approach with added benefits including a shorter operative time, a potential decrease in complication rate due to the smaller incision size, reduced postoperative pain and discomfort, and improved wound healing [29]. Alternatively, the transmastoid approach, first reported in North America in 2008, has been used as a less invasive approach as it avoids having to perform a craniotomy and can be performed under local anesthesia [30]. The transmastoid approach has been used with both canal plugging and modified resurfacing techniques. It involves a standard mastoidectomy that provides visualization of the superior semicircular canal. However, unlike the middle fossa approach, the transmastoid approach does not achieve direct visualization of the dehiscence over the semicircular canal [28,30–32]. More recently, endoscopic approaches have been described to perform plugging and resurfacing. The endoscopic approach utilizes a smaller keyhole craniotomy (approximately 3 2 cm), requires less retraction of the temporal lobe, and provides improved visualization of the dehiscence [28,33].
Please cite this article in press as: Mau C et al. Superior semicircular canal dehiscence: Diagnosis and management. J Clin Neurosci (2017), https://doi.org/ 10.1016/j.jocn.2017.11.019
Study
No. Patients (No. ears)
Approach
Technique
Material
Results
Amoodi et al. (2011) [37] Beyea et al. (2012) [32]
4 (5)
Transmastoid
Resurfacing
16 patients (Includes 3 from Agrawal et al. (2008) [30]) 19 with follow-up
Transmastoid
Plugging
Silastic with bone pâté or fascia Bone pâté
Postoperatively all patients experienced disequilibrium which resolved in all but 1 (bone pâté) 15 with complete resolution, 1 with vestibular symptoms not improved. 2 with small dural tears that were repaired
Middle fossa
Carter et al. (2014) [33] Crane et al. (2010) [38] Friedland et al. (2006) [45] Hahn et al. (2010) [50]
5 19 (19) 2
Endoscopic Middle fossa Middle fossa
Plugging (18), Resurfacing (1) Plugging Plugging Resurfacing
Fascia and bone graft (plugging and resurfacing) Fascia graft Fascia graft Fascia graft
2 patients (11%) with global vestibular hypofunction, all exhibited superior canal hypofunction All reported improvement in symptoms. 14 with complete resolution of autophony, 2 decreased to mild symptoms. Study specifically examined 2 patients with return of symptoms due to bone resorption
3
Middle fossa
Resurfacing
Hillman et al. (2006) [46] Janky et al. (2012) [40]
13 (16)
Middle fossa
Capping
All 3 with complete resolution of symptoms except for 1 with only partial resolution of hearing loss. 1 with continued vestibular symptoms and 1 with hearing loss.
20
Middle fossa
Plugging and resurfacing
Silastic with bone pâté or fascia Fascia graft and hydroxyapatite bone cement Fascia and bone pâté
Limb et al. (2006) [41]
19 without previous surgery, 10 with previous surgery 11 (11)
Middle fossa
Plugging and/or resurfacing
Fascia and bone graft
Middle fossa
Plugging (10) and resurfacing (1)
Bone Wax
5 (6)
Middle fossa
Fascia and bone pâté
1 (1)
Transcanal
Plugging (5) and resurfacing (1) Round window occlusion
19
Transcanal
5 (5) 40 (43) 10 (11)
Carey et al. (2007) [36]
Mikulec et al. (2005) [39] Phillips et al. (2010) [43] Silverstein et al. (2009) [34] Silverstein et al. (2014) [35] Teixido et al. (2011) [51] Ward et al. (2012) [42] Zhao et al. (2012) [31]
Transmastoid
Round window reinforcement – delicate coverage (19) Resurfacing
Cartilage, bone wax, perichondrium Fascia, cartilage, perichondrium, adipose, gelfoam and/or silastic Fascia and bone pâté
Middle fossa Transmastoid
Plugging Plugging
Fascia and bone graft Fascia and bone pâté
Spontaneous nystagmus (6/10 patients) and post head-shaking nystagmus (8/10 patients). 10/10 patients with positive head impulse test. Immediately post-op, increased fall risk. Patients with previous stapes procedure (1) and semicircular repair (2) had postoperative hearing loss. 2 of 6 surgery naïve patients with preoperative hearing loss had further hearing loss. 1 with mild hearing loss, 2 with both mild hearing loss and vestibular hypofunction. 10 (plugging) with significant reduction or complete resolution of symptoms. 1 unsuccessful (resurfacing) 1 with moderate vertigo, 2 with minimal vertigo. Transient hearing loss in 3 patients (1 resurfacing, 2 plugging) Complete resolution of symptoms Improvement in 8 symptoms, but worsened hearing loss
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No hearing loss. 1 with mild disequilibrium treated with tympanostomy tube Mild hearing loss in 25% of patients Hearing preservation in all patients, minor imbalance and tinnitus in 6 patients. Vertigo and phonophobia in 1 patient
5
Please cite this article in press as: Mau C et al. Superior semicircular canal dehiscence: Diagnosis and management. J Clin Neurosci (2017), https://doi.org/ 10.1016/j.jocn.2017.11.019
Table 3 Surgical repair technique and approach used to treat Superior Semicircular Canal Dehiscence.
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Another minimally invasive approach is occlusion of the round window through a transcanal or endaural approach [28,34,35]. This economical approach can be performed in an outpatient same-day surgery setting, decreased anesthesia time (either general anesthesia or local with intravenous sedation), and eliminated need for ICU stay [35]. Identifying the round window membrane and reinforcing it by overlying with another material, the idea is to occlude the round window and eliminate a ‘‘third window” effect. In practice, this approach eliminated Tullio’s phenomenon and autophony [28,34,35]. Additionally, the approach achieved the same level of symptom improvement as studies that utilized other approaches [49]. Different materials have been tried including fascia and cartilage grafts, bone wax and perichondrium for reinforcement. The use of a fascia graft only as the occluding material may decrease the longevity of this treatment because it has been reported to fail as early as 6 months after treatment [28]. The three repair techniques: resurfacing, capping and plugging, are all designed to eliminate the third window, thus eliminating the symptoms of SSCD. Initially, treatment involved resurfacing the tegmen floor using fascia, bone graft, and glue through a middle fossa approach [1]. However, it was later discovered that in reality there was occlusion of the SSC in these patients [36]. Strictly, canal resurfacing involves the use of bone graft or cartilage to cover the dehiscence without occluding the canal. Capping is a modification to the resurfacing technique which uses hydroxyapatite bone cement to seal the dehiscence. Resurfacing and capping seal off communication between the labyrinth and the brain [37]. Plugging involves drilling the dehiscence to open the canal further and then occluding it using either bone wax or temporalis fascia or plugging the superior SSC lumen distal and proximal to the dehiscence. When comparing the three techniques, the resurfacing method of management is significantly less effective than both plugging and capping [34]. Using the middle fossa approach, the three aforementioned techniques can be utilized. However, plugging is most often reported in the literature, (Table 2). Plugging provides relief of Tullio’s phenomenon, Hennebert’s sign, and autophony within one month after surgery [38]. It also may improve chronic disequilibrium, which is the most debilitating, although not a universal symptom of SSCD [39]. However, other studies suggest complications associated with plugging including global vestibular hypofunction, no improvement in bone-conduction hyperacusis, and
deficits in vestibule-ocular reflex function [34,36,39–41]. Some studies have also suggested a higher risk of mild high-frequency sensorineural hearing loss with plugging, secondary to the manipulation of the membranous labyrinth and possible damage to the cochlea from insertion of the plugging materials [37,42]. However, the latter cause was only found in patients who underwent previous procedures involving the cochlea or labyrinth [41,43]. Resurfacing through the middle cranial fossa approach is generally unsuccessful and has a higher failure rate [44,45]. Resurfacing typically uses a combination of fascia and bone graft. The fascia has been shown to atrophy and the bone graft can be resorbed or migrate, resulting in relapse of SSCD symptoms months after treatment. Half of patients treated with resurfacing have relapse of symptoms [44]. Canal capping using hydroxyapatite has a high success rate in resolving preoperative symptoms of Tullio phenomenon and autophony (Fig. 2). However, it is less successful in resolving hyperacusis [2]. Nevertheless, it has an overall success rate that is comparable to that of plugging [2,44,46]. Recent investigation of SSCD repair techniques in cadavers have suggested that a combination of plugging and capping is superior to plugging alone [47]. The transmastoid approach can be used to perform plugging and modified resurfacing techniques [48]. As discussed above, plugging is successful in relieving autophony, Tullio’s phenomenon, hyperacusis, positional vertigo, and generally has good preservation of hearing [31,32]. Additionally, the transmastoid approach combined with resurfacing has been shown to be the best surgical treatment to treat ear fullness [48]. However, there is an increased chance of postoperative imbalance and tinnitus, and sometimes mild sensorineural hearing loss [28,31,32]. Also, while no significant difference has been shown between the transmastoid approach and the middle fossa approach, a difference in admission length, adverse events, and total follow-up time is observed with the transmastoid approach being the safer alternative to the middle fossa approach. However, this can be due to the fact that more patients are treated with the middle fossa approach with plugging and are subjected to a higher complication risk associated with intracranial procedures. In an effort to reduce the risk of craniotomy-related complications, a growing number of studies implement the transmastoid approach combined with the plugging technique to rectify the dehiscence [48,49].
Fig. 2. Intraoperative imaging of the SSCD from the middle fossa approach. (A) The SSCD can be seen via the middle fossa approach. The temporal lobe is retracted superiorly extradurally to expose the superior semicircular canal. The greater superficial petrosal nerve (GSPN) is seen in this exposure. (B) Capping with hydroxyapatite bone cement is utilized to repair the SSCD defect.
Please cite this article in press as: Mau C et al. Superior semicircular canal dehiscence: Diagnosis and management. J Clin Neurosci (2017), https://doi.org/ 10.1016/j.jocn.2017.11.019
C. Mau et al. / Journal of Clinical Neuroscience xxx (2017) xxx–xxx
Another technique that has been reported is the modified resurfacing [38,48]. Although resurfacing has been relatively unsuccessful previously due to atrophy and resorption of the fascia and bone grafts, modified resurfacing uses a small silicone elastomer (Silastic) sheeting material between the dura and the dehiscence to reinforce either bone pâté or fascia. In the reported cases of modified resurfacing technique using silastic, all patients experienced nearly complete resolution of preoperative symptoms and had preservation of hearing [37,50]. Since silastic material is used, there is a lower risk of resorption. Modified resurfacing has also been performed using a soft tissue graft of tragal perichondrium [51]. Overall, patients reported a lower mean number (i.e., 5.4) of symptoms and signs postoperatively when compared to a higher mean number (i.e., 12.2) of symptoms and signs preoperatively [51]. Hearing abilities were preserved in all patients [51]. There have been two reports of endoscopic middle fossa approaches to repair SSCD [28,33]. One report used a 0-degree endoscope and attempted resurfacing using hydroxyapatite bone cement. The authors used a 2-cm circular craniotomy to access the dehiscence and required less retraction of the temporal lobe. They reported a greater than 93% success rate in eliminating preoperative symptoms [28]. The other report used a 30-degree endoscope and a 3 2 cm craniotomy [33]. The endoscopes allowed for direct visualization of the defect in the arcuate eminence. The authors used bone wax to plug the superior semicircular canal in this study. All the patients reported improvement of their preoperative symptoms. Of the patients tested, hearing was preserved when compared to preoperative audiometry testing. In a recent systematic review assessing the surgical repair techniques for SSCD repair found that there was no significant difference between the plugging, capping, resurfacing, and plugging with resurfacing [52]. There were also no significant differences in outcome between the middle fossa and transmastoid approaches. Thus, surgical treatment for the patients experiencing severe symptoms of SSCD is safe and feasible. 6. Conclusion Superior Semicircular Canal Dehiscence (SSCD) is still a relatively new pathologic condition that requires a high clinical suspicion for its correct diagnosis. Varied symptoms and presentations highlight the importance of other diagnostic tools including audiovestibular testing and imaging studies that are necessary for proper diagnosis of SSCD. While different surgical approaches and techniques have been published in the literature, with the middle fossa approach as the standard and most familiar approach for both neurosurgeons and otolaryngologists, more investigation is needed to determine the outcomes and efficacy of treatment with other more recently described techniques. Newer modifications to the middle fossa approach suggest added benefits related to reduced complication rates and operative time. As we learn more about that pathophysiology of SCCD, more precise diagnostic tools and surgical strategies will be available to properly diagnose and treat this elusive medical condition. Conflict of interest and source of funding The authors have no personal, financial, consultant or institutional interest in any of the drugs, material, or devices described in this article. Appendix A. Supplementary data Supplementary data associated with this article can be found, in the online version, at https://doi.org/10.1016/j.jocn.2017.11.019.
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