Third Window Syndrome: An Up-to-Date Systematic Review of Causes, Diagnosis, and Treatment

Ilias Lazarou; Giorgos Sideris; Nikolaos Papadimitriou; Alexander Delides; George Korres

doi:10.7874/jao.2024.00696

J Audiol Otol > Volume 29(2); 2025 > Article

Lazarou, Sideris, Papadimitriou, Delides, and Korres: Third Window Syndrome: An Up-to-Date Systematic Review of Causes, Diagnosis, and Treatment

Review

Journal of Audiology and Otology 2025;29(2):86-94.

Published online: April 18, 2025

DOI: https://doi.org/10.7874/jao.2024.00696

Third Window Syndrome: An Up-to-Date Systematic Review of Causes, Diagnosis, and Treatment

Ilias Lazarou

, Giorgos Sideris

, Nikolaos Papadimitriou

, Alexander Delides

, George Korres

2nd Otolaryngology Department, School of Medicine, National and Kapodistrian University of Athens, "Attikon" University Hospital, Athens, Greece

Address for correspondence Giorgos Sideris, MD, PhD 2nd Otolaryngology Department, “Attikon” University Hospital, Rimini 1, Chaidari, Athens 124 62, Greece Tel +302105831393 E-mail siderisgior@gmail.com

Received December 5, 2024 Revised January 11, 2025 Accepted February 17, 2025

This is an Open Access article distributed under the terms of the Creative Commons Attribution Non-Commercial License (http://creativecommons.org/licenses/by-nc/4.0/) which permits unrestricted non-commercial use, distribution, and reproduction in any medium, provided the original work is properly cited.

Abstract

Third window syndrome (TWS) is an inner ear condition caused by an additional compliant point in the otic capsule that disrupts auditory and vestibular functions. Superior semicircular canal dehiscence is the most common cause, presenting with hearing loss, vertigo, and autophony, significantly impairing quality of life. This study evaluated the pathophysiology, diagnostics, treatments, and recent advancements in TWS while identifying research gaps. Using the Preferred Reporting Items for Systematic Reviews and Meta-Analyses guidelines, 70 studies from Embase, MEDLINE, Cochrane, and UpToDate databases were analyzed. TWS affects inner ear mechanics, enhancing bone conduction and reducing air conduction. Diagnosis involves clinical evaluations, high-resolution imaging, and functional tests such as vestibular evoked myogenic potentials, which are known for their high sensitivity and specificity. Management strategies range from vestibular rehabilitation and pharmacotherapy to surgical interventions, including transmastoid and middle cranial fossa approaches, which achieve over 75% success. Emerging minimally invasive techniques, such as underwater endoscopic ear surgery and round window reinforcement, show promise but carry risks like cerebrospinal fluid leakage and inconsistent symptom relief. Advancements in TWS management have improved outcomes, yet gaps remain, particularly in terms of false-positive imaging and long-term efficacy. Future studies should prioritize predictive models and minimally invasive techniques. A multidisciplinary approach is essential to improve patient care.

Keywords: Third window syndrome · Superior semicircular canal dehiscence · Hearing loss · Vestibular evoked myogenic potentials · Surgical management.

Introduction

The superior semicircular canal dehiscence (SSCD) syndrome was first described in 1998 by Minor, et al. [1], who analyzed eight cases of dizziness and oscillopsia associated with sound or pressure stimuli and confirmed the presence of the dehiscence using computed tomography (CT). Subsequent studies validated this pathology as a cause of vertigo and auditory disturbances, while surgical repair improved symptoms in many patients [2].

Studies on temporal bones have shown that 0.7% of the general population has a complete dehiscence and 1.3% has a thin bony layer in the superior semicircular canal [3]. Additionally, Cremer, et al. [4] documented the correlation between sound stimuli and vestibular responses through oculomotor measurements. Experimental studies in animals supported the pathophysiology of the syndrome, demonstrating changes in vestibular nerve activity under conditions of increased external auditory canal pressure [5].

Recent research has highlighted the presence of dehiscence in other semicircular canals, such as the posterior canal, with a higher prevalence in individuals with a history of vertigo [6].

Pathophysiology

In the inner ear, the oval and round windows act as compliant points, facilitating the transfer of sound pressure [7]. The creation of a “third window,” such as the SSCD or an enlarged vestibular aqueduct (EVA), disrupts this physiology, causing changes in pressure transmission within the inner ear [8]. This causes sound energy from air conduction to be directed toward the compliant point and weakened, while sound energy from bone conduction is amplified due to the increased compliance of the system [9,10].

These disorders lead to hearing loss, vertigo due to the Tullio phenomenon, nystagmus from pressure changes (Hennebert sign), and pulsatile tinnitus due to pressure transmission from cerebrospinal fluid (CSF) [11-13]. This pathology highlights the complex interaction between normal pressure regulation and auditory function. Furthermore, SSCD or an EVA causes pressure transmission from CSF to the cochlea, resulting in perceived pulsations and pulsatile tinnitus due to arterial waves [14].

Definition

The term “third window syndromes” (TWS) refers to the clinical entities arising from the creation of a third compliant point in the bony capsule of the inner ear, making the inner ear sensitive to changes in pressure from the outer and middle ear, as well as intracranial pressure.

This study aims to review the existing literature on TWS, its pathophysiology, diagnosis, and treatment, while highlighting recent advancements in these areas.

Materials and Methods

A literature search was conducted using the Embase, MEDLINE, Cochrane, and UpToDate databases until June 2024. The following keywords were used: “third window,” “third window syndrome,” “canal dehiscence,” “superior semicircular canal dehiscence,” “SSCD,” “superior canal dehiscence,” “superior semicircular dehiscence,” “canal dehiscence,” “vestibular aqueduct,” “enlarged vestibular aqueduct,” “EVA syndrome,” “third window AND symptoms,” “Meniere,” “Meniere’s disease,” “Meniere AND third window,” “cochlear aqueduct,” “enlarged cochlear aqueduct,” “DFNX2,” “X-linked deafness,” “stapes gusher,” “inner ear anatomy,” “ear anatomy,” “ear physiology,” “hearing physiology,” “VEMPs,” “cVEMPs,” “oVEMPs,” “vestibular evoked myogenic potentials,” “audiometry,” “air-bone gap AND [third window OR SSCD],” “[third window OR SSCD] AND hearing loss,” “air-bone gap AND SSCD,” “pseudoconductive hearing loss,” “autophony,” “pressure induced vertigo,” “[third window OR SSCD] AND diagnosis,” “[third window OR SSCD] AND imaging,” “[third window OR SSCD] AND [computed tomography OR CT],” “[third window OR SSCD] AND [high resolution computed tomography OR HRCT],” “third window lesions,” “third window AND differential diagnosis,” “[third window OR SSCD] AND prevalence,” “Tullio phenomenon,” “Tullio sign,” Hennebert sign,” “Valsalva maneuver,” “Toynbee phenomenon,” “ankle audiometry,” “[third window OR SSCD] AND treatment,” “[third window OR SSCD] AND surgical management,” “canal plugging.”

The research methodology was used according to PRISMA (Preferred Reporting Items for Systematic Reviews and Meta-Analyses) guidelines along with PICOS (Participants, Interventions, Comparisons, Outcomes, and Study design) criteria. English language, ability to extract data, and similarity with the subject were used as inclusion criteria.

Results and Discussion

Literature research led to 174 abstracts. After review, 78 articles were excluded for being non-English, not published yet, having a misleading title, or outcomes not discussed in the abstract. A total of 96 articles were fully reviewed, but 26 were excluded due to possible plagiarism, outcomes not discussed, being too concise, or having no meaningful analysis. In total, 70 studies were included (Fig. 1).

Epidemiology

The prevalence of SSCD ranges from 0.5% to 1.4% in anatomical studies [3,15], while thinning of the canal wall is more commonly observed in older individuals due to reduced bone mass [16]. In high-resolution computed tomography (HRCT) imaging studies, prevalence ranges from 3% to 10%, though it is often overestimated due to technical limitations [17]. Although the bony wall is thinner in women, the prevalence of the condition is equal between the two genders [18].

Etiology

SSCD is the most common cause of a third window, resulting from incomplete development of the petrous bone or external factors such as trauma or increased intracranial pressure [19,20]. Less common causes include dehiscence in other semicircular canals [21] and an EVA, which occurs when its diameter does not decrease normally during development [22].

Bone erosion is also common in conditions such as chronic otitis media or trauma, particularly in the horizontal semicircular canal due to its proximity to the tympanic cavity [23]. Rarely, the DFNX2 mutation causes communication between the internal auditory canal and the inner ear, leading to hearing loss [24]. Other causes include Paget’s disease, which thins the cochlear capsule, and the “two-hit model,” where a thin bone fractures following trauma, the development of intracranial hypertension, diving, or even childbirth [25-27].

Medical history and symptoms

Patients present with a variety of symptoms, including dizziness, vertigo, instability, autophony, hearing loss, hyperacusis, pulsatile tinnitus, and a sensation of fullness [28]. Autophony involves an increased perception of one’s own voice and bodily movements due to increased bony conduction, while pulsatile tinnitus is often caused by adjacent blood vessels whose hydrostatic pressure is transferred to inner ear fluids through third window [29].

Dizziness is often caused by changes in pressure or loud sounds (Hennebert and Tullio signs) and may be accompanied by nystagmus, with episodes of falls or oscillopsia also having been recorded. The presence of a third compliance point makes the inner ear’s structure more susceptible either to atmospheric or sound pressure which is transferred to vestibular endolymph setting semicircular canal cupulae in movement [30,31].

Clinical assessment

The diagnosis requires a comprehensive otolaryngological examination to rule out other causes. Findings such as lateralization of Weber’s test to the affected ear and a potentially negative Rinne test are indicative but not pathognomonic.

Special tests, inducing nystagmus using Frenzel goggles or videonystagmography, are useful. Tullio sign is triggered by loud sounds, while Hennebert sign is elicited by pressure increases in the external ear. The Valsalva maneuver, either by equalizing middle ear pressure or increasing intracranial pressure, can confirm the diagnosis by inducing nystagmus. For greater accuracy, testing in the supine position is recommended to avoid false-negative results [32].

The Toynbee maneuver, performed by swallowing with closed nostrils, can also induce nystagmus in cases of TWS, although the underlying mechanism remains unclear [33].

Audiometry

Pure tone audiometry

The most common finding in audiometry is an air-bone gap at low frequencies (250–2,000 Hz), with the largest difference observed at 250 Hz (27.52 dB), which gradually decreases up to 2,000 Hz [34]. Larger SSCD are associated with greater gaps [35]. The bone conduction threshold is often better than normal or even negative at low frequencies. The Weber test using a 512 Hz tuning fork can confirm the gap, with the sound being perceived more intensely in the affected ear [36].

Ankle audiometry

The study by Verrecchia, et al. [37] proposed ankle audiometry as a diagnostic tool for SSCD. Using a device that generated controlled bone vibrations (125–750 Hz), it was found that thresholds were reduced in patients compared to the control group, with the greatest difference observed at 250 Hz. Following surgical repair, thresholds increased by 20 dB, supporting the test’s utility both for diagnosis and for assessing treatment outcomes.

Vestibular evoked myogenic potentials

Vestibular evoked myogenic potentials (VEMPs) are highly sensitive and specific tests for detecting TWS, particularly SSCD. Cervical VEMPs (cVEMPs) are recorded at a reduced threshold, with sensitivity and specificity >90%, while ocular VEMPs (oVEMPs) exhibit greater response and higher sensitivity [38,39]. The use of high frequencies, such as 4,000 Hz, improves accuracy, as otolithic organs are more sensitive to these frequencies. Studies have shown this approach achieves a 100% positive predictive value [40,41]. VEMPs can confirm clinical and radiological findings or assess postoperative outcomes. The cVEMP and oVEMP tests have been recognized as reliable diagnostic methods, with their values returning to normal levels following surgical repair [42].

Electrocochleography

Electrocochleography records the electrical activity of the cochlea and the vestibulocochlear nerve in response to sound stimuli. It involves placing an electrode on the tympanic membrane. Patients with SSCD exhibit an increased summating potential/action potential (SP/AP) ratio, which improves following surgical repair [43]. However, this test is now largely confined to research protocols due to technical challenges and the availability of more reliable alternative methods [44].

Imaging

Superior semicircular canal dehiscence

HRCT with slice thicknesses of 0.5–0.6 mm improves the sensitivity of diagnosing SSCD from 50% to 93% and reduces false-positive results [45]. For better visualization, reconstructions in the Pöschl and Stenver planes are recommended, although their effectiveness remains debated [46]. The dehiscence is typically found in the projection of the canal toward the middle cranial fossa and is often associated with a thin bony plate or meningocele. Increased pneumatization of the mastoid is correlated with a thinner bony covering and a higher risk of dehiscence [47]. Cone beam computed tomography (CBCT) is a newer technique mainly used in oral and maxillofacial radiology due to its ability to produce detailed 3D images with less radiation than CT. When properly used, it can exceed CT’s sensitivity in the identification of SSCD [48].

Horizontal and posterior semicircular canal dehiscence

Dehiscence of the horizontal and posterior semicircular canals is a rare cause of TWS and is often accompanied by other inner ear abnormalities. On HRCT, horizontal canal dehiscence is frequently associated with middle ear conditions such as chronic otitis media and cholesteatoma, due to proteolytic enzymes that erode the otic capsule [49]. Posterior canal dehiscence can be caused by a high-riding jugular bulb or paraganglioma, with characteristic imaging findings [50].

Enlarged vestibular aqueduct

An EVA creates a communication between the subarachnoid space and the otic capsule, leading to TWS symptoms. Normally, its width ranges from 0.4–1.0 mm, and it is considered pathological if it exceeds 1.5 mm on CT scans [51]. More recent criteria define a pathological width as >1.0 mm at the midpoint, >2.0 mm at the aperture, or >0.9 mm in the Pöschl plane [52]. Magnetic resonance imaging with T2-weighted sequences can reveal an enlarged endolymphatic sac up to 2 cm [53]. An EVA is associated with CSF leakage during surgical procedures and an increased risk of sensorineural hearing loss following trauma [54].

X-linked hearing loss DFNX2 mutation

This is a genetic disorder characterized by the absence of the cribriform plate between the basal turn of the cochlea and the fundus of the internal auditory canal, leading to progressive hearing loss. On HRCT, a triad of findings is observed: incomplete partitioning of the cochlea (type III), enlargement of the internal auditory canal, and an abnormal course of the facial nerve [24]. The condition is associated with CSF gusher during stapedectomy, necessitating avoidance of the procedure. Additional anomalies may include an enlarged facial nerve canal, cystic vestibule, oval window dysplasia, and stapes abnormalities such as stapes fixation, thickened footplate or single crus [55].

Paget’s disease

The hallmark imaging finding of Paget’s disease is a “cotton wool” appearance on skull radiographs. CT scans reveal irregular areas of sclerotic bone, cortical thickening, and exostoses, reflecting the coexistence of osteoblastic and osteoclastic activity [56].

Case reports

Rarely, dehiscences have been observed in the fallopian canal and carotid canal, causing third window symptoms due to bone loss in the otic capsule. Blake, et al. [57] reported two adults with unilateral hearing loss, autophony, and dizziness, where HRCT revealed a dehiscence between the cochlea and the labyrinthine segment of the facial nerve. In a 20-monthold infant with abnormal auditory brainstem responses, Koroulakis, et al. [58] identified a similar dehiscence. Kim and Wilson [59] described an ectopic position of the carotid canal in contact with the apex of the cochlea, with a bony defect diagnosed following a failed stapedectomy.

Differential diagnosis

TWS causes both auditory and vestibular symptoms, with its differential diagnosis including middle ear disorders, patulous Eustachian tube, vestibular migraine, vestibular schwannoma, Ménière’s disease, and perilymphatic fistula [10,36,60-64]. The differential diagnosis of TWS compared to other diseases according to symptoms, auditory thresholds, and diagnostic markers like oVEMP and cVEMP characteristics is presented in Table 1.

Conservative treatment

In the initial management, conservative measures and strategies can be employed to alleviate symptoms. Lifestyle modifications are recommended, such as avoiding triggering stimuli like loud noise. Earplugs are particularly useful for preventing dizziness caused by the Tullio phenomenon. Vestibular rehabilitation appears effective in cases of low-intensity chronic dizziness. Symptom relief can be achieved with labyrinthine suppressants, H3 histamine receptor antagonists, or benzodiazepines [65]. Another proposed treatment is the insertion of ventilation tubes. The rationale behind this approach is to relieve middle ear pressure, which is transmitted to the inner ear due to its increased compliance with pressure changes. However, this method does not seem effective for intracranial pressure changes, such as those caused by head tilting [66].

Surgical intervention

In patients with severe chronic symptoms unresponsive to conservative measures, surgical management is performed. Improvements and considerations are noted for various causes of TWS such as superior and posterior semicircular canal dehiscence, EVA, X-linked hearing loss, and perilymphatic fistula [67-70] (Table 2). The most commonly applied surgical techniques involve closure of the dehiscence via the cranial fossa or mastoid approach, as well as reinforcement of the round or oval windows. In cases of bilateral TWS, such as SSCD, surgery is recommended initially for the ear with the more severe symptoms. However, restoration on one side can potentially worsen the other side, particularly in cases of thin bone. A possible explanation is that intracranial hypertension is redirected to the second compliant point. Despite the high effectiveness of bilateral correction in symptom control, there is a risk of developing oscillopsia due to the destruction of both vestibules [71].

Regarding effectiveness, according to the study by Mekonnen, et al. [72], involving 350 patients who underwent surgical repair of SSCD, improvements were observed in 74.9% of cases for autophony, 62.9% for hearing, and 54.6% for dizziness. Unilateral repair showed slightly better outcomes than bilateral intervention, while repeat surgery increased improvement rates to 85%. Similarly, in the study by Mozaffari, et al. [73] involving 229 cases, unilateral intervention demonstrated better results in hyperacusis, hearing loss, dizziness, and instability compared to bilateral intervention, leaving open the question of the necessity for bilateral procedures. Postoperative CSF leakage was observed in up to 25% of cases, mostly managed conservatively. Risk factors include hypertension, obesity, and increased intracranial pressure [74]. Other studies are more conservative reporting lower rates of symptom relief after surgery and the possible need for a second intervention [75]. It has to be noted that plugging SSCD can lead to deterioration of bone conduction thresholds [76].

Repair of dehincence via the transmastoid approach

The transmastoid approach provides an alternative method for repairing SSCD through mastoidectomy, without the need for craniectomy or manipulation of the brain. It is less invasive and can be performed without a neurosurgeon, while offering similar effectiveness to the middle cranial fossa approach [77].

An innovative technique within this approach is underwater endoscopic ear surgery (UWEES), which utilizes an endoscope submerged in saline for enhanced visualization. This method is minimally invasive and effective in reducing autophony and dizziness. However, temporary hearing loss is frequently observed, with long-term improvement over time [78,79].

Repair of dehinscence via the middle cranial fossa

The first successful repair of SSCD was performed using muscle fascia. Today, various materials are used, including bone paste, cortical bone, wax, and hydroxyapatite cement.

The repair techniques include: 1) plugging: the dehiscence is filled with material (e.g., bone paste) and covered with fascia; 2) resurfacing: the dehiscence is externally covered with materials such as cortical bone and fascia; and 3) capping: a rigid material (e.g., hydroxyapatite cement) is wedged into the defect and secured with glue or bone paste.

Plugging and capping are more effective than resurfacing, but plugging is associated with more complications. However, some reviews find no significant differences in effectiveness among the methods [80,81].

Reinforcement of the round and oval windows

In 2014, an alternative approach for treating TWS was proposed, where instead of closing the dehiscence, reinforcement of the round or oval window is performed, leaving only two compliant points. The procedure involves creating a tympanomeatal flap, identifying the windows, and reinforcing one of them with cartilage from the tragus and fibrin glue [82]. By increasing the stiffness of the inner ear, this method reduces hyperacusis, dizziness, and the Tullio phenomenon, while cVEMP thresholds return to normal levels [83].

The effectiveness of this method has not been fully established, with outcomes often inconsistent. Despite positive results in some patients, preoperative prediction of success remains challenging [84]. The procedure has a favorable safety profile with mild complications, although a consistent threshold drop at 4,000 Hz has been observed, without clinical impact on speech audiometry [85].

Due to its low morbidity, this approach is recommended for elderly patients or those with comorbidities, as well as in cases with hearing loss in the contralateral ear, where preserving hearing is critical [86].

Future directions

Future research in TWS should prioritize several key areas to enhance patient care and outcomes. First, the development of predictive models for surgical outcomes is essential to optimize patient selection and tailor treatment strategies effectively. Standardizing and refining diagnostic criteria are equally important to reduce false-positive rates, which currently pose a challenge in accurately identifying TWS cases. Additionally, exploring long-term outcomes and patient satisfaction across both surgical and non-surgical interventions will provide valuable insights into the durability and effectiveness of current treatment modalities. Investigating the pathophysiological mechanisms underlying less common forms of TWS is another critical area, as it may uncover novel therapeutic options and broaden the scope of treatment. Finally, evaluating minimally invasive techniques, such as UWEES, in larger cohorts is vital to establish their safety, efficacy, and potential advantages over traditional approaches. These research directions collectively aim to address existing gaps in knowledge, refine clinical practices, and ultimately improve outcomes for patients with TWS.

Conclusion

TWS can be either congenital or acquired. By far, the most common cause is SSCD, due to its close proximity to the middle cranial fossa. Less common locations include the posterior and horizontal semicircular canals, an enlarged vestibular or cochlear aqueduct, X-linked hearing loss DFNX2, and Paget’s disease. Its prevalence in the general population is approximately 0.5%, increasing with age, but it does not differ between genders.

The pathophysiology involves the creation of a third compliant point in the inner ear, in addition to the two normal ones—the oval and round windows. This reduces the stiffness of the system, enhancing bone conduction while impairing air conduction.

Clinical suspicion is of high importance, while VEMPs are highly sensitive diagnostic tests for TWS. cVEMPs are elicited at lower thresholds, while oVEMPs exhibit larger amplitudes. HRCT and CBCT are an important diagnostic tool, enabling the identification of dehiscence, but they have a high rate of false positives, necessitating a combination of diagnostic methods.

The management of TWS has seen significant advancements, with treatments ranging from conservative measures to highly specialized surgical interventions. Initial management focuses on symptom relief through lifestyle modifications, vestibular rehabilitation, and pharmacological approaches, such as labyrinthine suppressants. Earplugs and strategies to avoid triggering stimuli are particularly effective for patients experiencing sound-induced dizziness. Surgical intervention is indicated in patients with refractory or severe symptoms. Techniques such as transmastoid or middle cranial fossa approaches have demonstrated success rates exceeding 75% for symptom improvement, particularly in vertigo and autophony. Novel approaches like UWEES and round window reinforcement offer promising results with reduced invasiveness, especially for elderly or high-risk patients. Comparative studies have yet to establish definitive superiority among surgical techniques, leaving room for further optimization of patient selection criteria and procedural protocols.

Despite these advances, gaps in the literature remain. The heterogeneity in patient outcomes points to the need for standardized evaluation frameworks and longitudinal studies to assess the durability of treatment benefits.

Notes

Conflicts of Interest

The authors have no financial conflicts of interest.

Author Contributions

Conceptualization: Ilias Lazarou, George Korres. Data curation: Ilias Lazarou, Giorgos Sideris. Formal analysis: Ilias Lazarou, Giorgos Sideris. Funding acquisition: Ilias Lazarou, Nikolaos Papadimitriou, Alexander Delides, George Korres. Investigation: Ilias Lazarou, George Korres. Methodology: Ilias Lazarou, Giorgos Sideris, George Korres. Project administration: Ilias Lazarou, George Korres. Resources: Ilias Lazarou, Nikolaos Papadimitriou, Alexander Delides, George Korres. Software: Ilias Lazarou. Supervision: Nikolaos Papadimitriou, Alexander Delides, George Korres. Validation: George Korres. Visualisation: Nikolaos Papadimitriou, Alexander Delides. Writing—original draft: Ilias Lazarou, Giorgos Sideris. Writing—review & editing: Giorgos Sideris, Nikolaos Papadimitriou, George Korres. Approval of final manuscript: all authors.

Funding Statement

None

Acknowledgments

None

Fig. 1.

PRISMA flowchart.

Table 1.

Differential diagnosis of third window syndrome compared to other diseases

Diseases	Disease to differentiate from	Third window syndrome
Middle ear disease	- Air-bone gap across all frequencies	- Air-bone gap ≤2,000 Hz
Middle ear disease	- Air-bone gap across all frequencies	- Bone thresholds can be ≤0 dB
Patulous Eustachian tube	- Autophony mainly of respiratory sounds and voice	- Autophony includes body sounds, e.g., eye movements, walking, heart beating
Vestibular migraine	- Way more frequent vertigo and photophobia	- Tullio’s phenomenon
Vestibular schwannoma	- Sensorineural hearing loss	- Pseudoconductive hearing loss
	- Absent oVEMPs/cVEMPs	- oVEMPs higher amplitude
		- cVEMPs lower thresholds
Ménière’s disease	- Sensorineural hearing loss	- oVEMPs higher amplitude
	- oVEMPs reduced amplitude	- cVEMPs lower thresholds
	- Free of symptoms between episodes	- No period free of symptoms
Perilymphatic fistula	- Sensorineural hearing loss	- Pseudoconductive hearing loss
Perilymphatic fistula	- Biomarkers such as cochlin-tomoprotein from middle ear fluid	- No middle ear fluid

oVEMPs, ocular vestibular evoked myogenic potentials; cVEMPs, cervical vestibular evoked myogenic potentials

Table 2.

Causes of TWS and related surgical outcomes

TWS cause	Surgical outcomes
Superior semicircular canal dehiscence	- Autophony improvement ＞75%
	- Air conduction hearing improvement ＞60%
	- Dizziness improvement about 50%
Posterior semicircular canal dehiscence	- Significant improvement of vestibular symptoms
Posterior semicircular canal dehiscence	- No evidence of hearing improvement
Enlarged vestibular aqueduct	- No definite treatment
	- Avoid head trauma
	- Steroids could improve sensorineural hearing loss
	- Endolymphatic Sac Surgery—few studies with favorable results
X-linked hearing loss	- No treatment
X-linked hearing loss	- Must avoid stapedectomy
Perilymphatic fistula	- Closure of air-bone gap
	- Dizziness improved in most patients
	- The earlier the intervention the better outcomes

TWS, third window syndromes

REFERENCES

1. Minor LB, Solomon D, Zinreich JS, Zee DS. Sound- and/or pressureinduced vertigo due to bone dehiscence of the superior semicircular canal. Arch Otolaryngol Head Neck Surg 1998;124:249–58.

2. Smullen JL, Andrist EC, Gianoli GJ. Superior semicircular canal dehiscence: a new cause of vertigo. J La State Med Soc 1999;151:397–400.

3. Carey JP, Minor LB, Nager GT. Dehiscence or thinning of bone overlying the superior semicircular canal in a temporal bone survey. Arch Otolaryngol Head Neck Surg 2000;126:137–47.

4. Cremer PD, Minor LB, Carey JP, Della Santina CC. Eye movements in patients with superior canal dehiscence syndrome align with the abnormal canal. Neurology 2000;55:1833–41.

5. Hirvonen TP, Carey JP, Liang CJ, Minor LB. Superior canal dehiscence: mechanisms of pressure sensitivity in a chinchilla model. Arch Otolaryngol Head Neck Surg 2001;127:1331–6.

6. Krombach GA, DiMartino E, Schmitz-Rode T, Prescher A, Haage P, Kinzel S, et al. Posterior semicircular canal dehiscence: a morphologic cause of vertigo similar to superior semicircular canal dehiscence. Eur Radiol 2003;13:1444–50.

7. Ramamoorthy S, Zha DJ, Nuttall AL. The biophysical origin of traveling-wave dispersion in the cochlea. Biophys J 2010;99:1687–95.

8. Rosowski JJ, Songer JE, Nakajima HH, Brinsko KM, Merchant SN. Clinical, experimental, and theoretical investigations of the effect of superior semicircular canal dehiscence on hearing mechanisms. Otol Neurotol 2004;25:323–32.

9. Mikulec AA, McKenna MJ, Ramsey MJ, Rosowski JJ, Herrmann BS, Rauch SD, et al. Superior semicircular canal dehiscence presenting as conductive hearing loss without vertigo. Otol Neurotol 2004;25:121–9.

10. Suzuki M, Ota Y, Takanami T, Yoshino R, Masuda H. Superior canal dehiscence syndrome: a review. Auris Nasus Larynx 2024;51:113–9.

11. Basura GJ, Cronin SJ, Heidenreich KD. Tullio phenomenon in superior semicircular canal dehiscence syndrome. Neurology 2014;82:1010

12. Connor SE, Sriskandan N. Imaging of dizziness. Clin Radiol 2014;69:111–22.

13. Shuman AG, Rizvi SS, Pirouet CW, Heidenreich KD. Hennebert’s sign in superior semicircular canal dehiscence syndrome: a video case report. Laryngoscope 2012;122:412–4.

14. Ward BK, van de Berg R, van Rompaey V, Bisdorff A, Hullar TE, Welgampola MS, et al. Superior semicircular canal dehiscence syndrome: diagnostic criteria consensus document of the committee for the classification of vestibular disorders of the Bárány Society. J Vestib Res 2021;31:131–41.

15. Tsunoda A, Terasaki O. Dehiscence of the bony roof of the superior semicircular canal in the middle cranial fossa. J Laryngol Otol 2002;116:514–8.

16. Davey S, Kelly-Morland C, Phillips JS, Nunney I, Pawaroo D. Assessment of superior semicircular canal thickness with advancing age. Laryngoscope 2015;125:1940–5.

17. Elmali M, Polat AV, Kucuk H, Atmaca S, Aksoy A. Semicircular canal dehiscence: frequency and distribution on temporal bone CT and its relationship with the clinical outcomes. Eur J Radiol 2013;82:e606–9.

18. Evlice B, Çabuk DS, Duyan H. The evaluation of superior semicircular canal bone thickness and radiological patterns in relation to age and gender. Surg Radiol Anat 2021;43:1839–44.

19. Takahashi N, Tsunoda A, Shirakura S, Kitamura K. Anatomical feature of the middle cranial fossa in fetal periods: possible etiology of superior canal dehiscence syndrome. Acta Otolaryngol 2012;132:385–90.

20. Nadgir RN, Ozonoff A, Devaiah AK, Halderman AA, Sakai O. Superior semicircular canal dehiscence: congenital or acquired condition? AJNR Am J Neuroradiol 2011;32:947–9.

21. Russo JE, Crowson MG, DeAngelo EJ, Belden CJ, Saunders JE. Posterior semicircular canal dehiscence: CT prevalence and clinical symptoms. Otol Neurotol 2014;35:310–4.

22. Gopen Q, Zhou G, Whittemore K, Kenna M. Enlarged vestibular aqueduct: review of controversial aspects. Laryngoscope 2011;121:1971–8.

23. Ho ML, Moonis G, Halpin CF, Curtin HD. Spectrum of third window abnormalities: semicircular canal dehiscence and beyond. AJNR Am J Neuroradiol 2017;38:2–9.

24. Dasgupta S, Hong J, Morris R, Iqbal J, Lennox-Bowley A, Saniasiaya J. X-linked gusher disease DFNX2 in children, a rare inner ear dysplasia with mixed hearing and vestibular loss. Audiol Res 2023;13:600–14.

25. Peng KA, Ahmed S, Yang I, Gopen Q. Temporal bone fracture causing superior semicircular canal dehiscence. Case Rep Otolaryngol 2014;2014:817291

26. Watters KF, Rosowski JJ, Sauter T, Lee DJ. Superior semicircular canal dehiscence presenting as postpartum vertigo. Otol Neurotol 2006;27:756–68.

27. Vargas-Figueroa VM, Cáceres-Chacón M, Labat EJ. Scuba diving-induced inner-ear pathology: imaging findings of superior semicircular canal and tegmen tympani dehiscence. Am J Case Rep 2024;25:e941558.

28. Bi WL, Brewster R, Poe D, Vernick D, Lee DJ, Eduardo Corrales C, et al. Superior semicircular canal dehiscence syndrome. J Neurosurg 2017;127:1268–76.

29. Naert L, Van de Berg R, Van de Heyning P, Bisdorff A, Sharon JD, Ward BK, et al. Aggregating the symptoms of superior semicircular canal dehiscence syndrome. Laryngoscope 2018;128:1932–8.

30. Minor LB, Cremer PD, Carey JP, Della Santina CC, Streubel SO, Weg N. Symptoms and signs in superior canal dehiscence syndrome. Ann N Y Acad Sci 2001;942:259–73.

31. Brantberg K, Ishiyama A, Baloh RW. Drop attacks secondary to superior canal dehiscence syndrome. Neurology 2005;64:2126–8.

32. Hoppes CW, Lambert KH, Zalewski C, Pinto R, Burrows H, McCaslin D. The supine superior semicircular canal dehiscence test. Am J Audiol 2021;30:475–80.

33. Finkelstein Y, Talmi YP, Zohar Y, Laurian N. Study of Toynbee phenomenon by combined intranasopharyngeal and tympanometric measurements. Ann Otol Rhinol Laryngol 1988;97(2 Pt 1):199–206.

34. McEvoy TP, Mikulec AA, Armbrecht ES, Lowe ME. Quantification of hearing loss associated with superior semi-circular canal dehiscence. Am J Otolaryngol 2013;34:345–9.

35. Chien WW, Janky K, Minor LB, Carey JP. Superior canal dehiscence size: multivariate assessment of clinical impact. Otol Neurotol 2012;33:810–5.

36. Ward BK, Carey JP, Minor LB. Superior canal dehiscence syndrome: lessons from the first 20 years. Front Neurol 2017;8:177

37. Verrecchia L, Fredén Jansson KJ, Westin M, Velikoselskii A, Reinfeldt S, Håkansson B. Ankle audiometry: a clinical test for the enhanced hearing sensitivity for body sounds in superior canal dehiscence syndrome. Audiol Neurootol 2023;28:219–29.

38. Zhou G, Gopen Q, Poe DS. Clinical and diagnostic characterization of canal dehiscence syndrome: a great otologic mimicker. Otol Neurotol 2007;28:920–6.

39. Zuniga MG, Janky KL, Nguyen KD, Welgampola MS, Carey JP. Ocular versus cervical VEMPs in the diagnosis of superior semicircular canal dehiscence syndrome. Otol Neurotol 2013;34:121–6.

40. Noij KS, Rauch SD. Vestibular evoked myogenic potential (VEMP) testing for diagnosis of superior semicircular canal dehiscence. Front Neurol 2020;11:695

41. Curthoys IS, Manzari L. A simple specific functional test for SCD: VEMPs to high frequency (4,000Hz) stimuli-their origin and explanation. Front Neurol 2020;11:612075

42. Welgampola MS, Myrie OA, Minor LB, Carey JP. Vestibular-evoked myogenic potential thresholds normalize on plugging superior canal dehiscence. Neurology 2008;70:464–72.

43. Arts HA, Adams ME, Telian SA, El-Kashlan H, Kileny PR. Reversible electrocochleographic abnormalities in superior canal dehiscence. Otol Neurotol 2009;30:79–86.

44. Park JH, Lee SY, Song JJ, Choi BY, Koo JW. Electrocochleographic findings in superior canal dehiscence syndrome. Hear Res 2015;323:61–7.

45. Belden CJ, Weg N, Minor LB, Zinreich SJ. CT evaluation of bone dehiscence of the superior semicircular canal as a cause of sound- and/ or pressure-induced vertigo. Radiology 2003;226:337–43.

46. Branstetter BF 4th, Harrigal C, Escott EJ, Hirsch BE. Superior semicircular canal dehiscence: oblique reformatted CT images for diagnosis. Radiology 2006;238:938–42.

47. Shim BS, Kang BC, Kim CH, Kim TS, Park HJ. Superior canal dehiscence patients have smaller mastoid volume than age- and sex-matched otosclerosis and temporal bone fracture patients. Korean J Audiol 2012;16:120–3.

48. Sepúlveda I, Schmidt T, Platín E. Use of cone beam computed tomography in the diagnosis of superior semicircular canal dehiscence. J Clin Imaging Sci 2014;4:49

49. Jang CH, Merchant SN. Histopathology of labyrinthine fistulae in chronic otitis media with clinical implications. Am J Otol 1997;18:15–25.

50. Gopen Q, Zhou G, Poe D, Kenna M, Jones D. Posterior semicircular canal dehiscence: first reported case series. Otol Neurotol 2010;31:339–44.

51. Valvassori GE, Clemis JD. The large vestibular aqueduct syndrome. Laryngoscope 1978;88:723–8.

52. Vijayasekaran S, Halsted MJ, Boston M, Meinzen-Derr J, Bardo DM, Greinwald J, et al. When is the vestibular aqueduct enlarged? A statistical analysis of the normative distribution of vestibular aqueduct size. AJNR Am J Neuroradiol 2007;28:1133–8.

53. Hirsch BE, Weissman JL, Curtin HD, Kamerer DB. Magnetic resonance imaging of the large vestibular aqueduct. Arch Otolaryngol Head Neck Surg 1992;118:1124–7.

54. Shirazi A, Fenton JE, Fagan PA. Large vestibular aqueduct syndrome and stapes fixation. J Laryngol Otol 1994;108:989–90.

55. Hong R, Du Q, Pan Y. New imaging findings of incomplete partition type III inner ear malformation and literature review. AJNR Am J Neuroradiol 2020;41:1076–80.

56. Bhargava P, Maki JH. Images in clinical medicine. “Cotton wool” appearance of Paget’s disease. N Engl J Med 2010;363:e9.

57. Blake DM, Tomovic S, Vazquez A, Lee HJ, Jyung RW. Cochlear-facial dehiscence--a newly described entity. Laryngoscope 2014;124:283–9.

58. Koroulakis DJ, Reilly BK, Whitehead MT. Cochlear-facial dehiscence in a pediatric patient. Pediatr Radiol 2020;50:750–2.

59. Kim HH, Wilson DF. A third mobile window at the cochlear apex. Otolaryngol Head Neck Surg 2006;135:965–6.

60. Sandhu JS, Low R, Rea PA, Saunders NC. Altered frequency dynamics of cervical and ocular vestibular evoked myogenic potentials in patients with Ménière’s disease. Otol Neurotol 2012;33:444–9.

61. Deveze A, Matsuda H, Elziere M, Ikezono T. Diagnosis and treatment of perilymphatic fistula. Adv Otorhinolaryngol 2018;81:133–45.

62. Gibson WPR. Meniere’s disease. Adv Otorhinolaryngol 2019;82:77–86.

63. Garrison D, Barth L, Kaylie D, Riska K. Symptoms, audiometric and vestibular laboratory findings, and imaging in a concurrent superior canal dehiscence syndrome and vestibular schwannoma: a case report. J Am Acad Audiol 2020;31:76–82.

64. Steenerson KK, Crane BT, Minor LB. Superior semicircular canal dehiscence syndrome. Semin Neurol 2020;40:151–9.

65. Wackym PA, Agrawal Y, Ikezono T, Balaban CD. Editorial: third window syndrome. Front Neurol 2021;12:704095

66. Teixeira EO, Fonseca MT. Superior semicircular canal dehiscence syndrome without vestibular symptoms. Int Arch Otorhinolaryngol 2014;18:210–2.

67. Beyea JA, Agrawal SK, Parnes LS. Transmastoid semicircular canal occlusion: a safe and highly effective treatment for benign paroxysmal positional vertigo and superior canal dehiscence. Laryngoscope 2012;122:1862–6.

68. Gubbels SP, Zhang Q, Lenkowski PW, Hansen MR. Repair of posterior semicircular canal dehiscence from a high jugular bulb. Ann Otol Rhinol Laryngol 2013;122:269–72.

69. Saliba I, Alshehri S, Fournier I, Altamami N. Large vestibular aqueduct-associated symptoms: endolymphatic duct blockage as a surgical treatment. Audiol Res 2024;14:304–16.

70. Sarna B, Abouzari M, Merna C, Jamshidi S, Saber T, Djalilian HR. Perilymphatic fistula: a review of classification, etiology, diagnosis, and treatment. Front Neurol 2020;11:1046

71. Niesten ME, McKenna MJ, Grolman W, Lee DJ. Clinical factors associated with prolonged recovery after superior canal dehiscence surgery. Otol Neurotol 2012;33:824–31.

72. Mekonnen M, Lum M, Duong C, Rana S, Mozaffari K, Hovis GEA, et al. Superior semicircular canal dehiscence postoperative outcomes: a case series of 350 repairs. Acta Neurochir (Wien) 2024;166:230

73. Mozaffari K, Willis SL, Unterberger A, Duong C, Hong M, De Jong R, et al. Superior semicircular canal dehiscence outcomes in a consecutive series of 229 surgical repairs with middle cranial fossa craniotomy. World Neurosurg 2021;156:e229–34.

74. Lobo BC, Baumanis MM, Nelson RF. Surgical repair of spontaneous cerebrospinal fluid (CSF) leaks: a systematic review. Laryngoscope Investig Otolaryngol 2017;2:215–24.

75. Powell HR, Khalil SS, Saeed SR. Outcomes of transmastoid surgery for superior semicircular canal dehiscence syndrome. Otol Neurotol 2016;37:e228–33.

76. Michailidou E, Rüegg PO, Karrer T, Korda A, Weder S, Kompis M, et al. Hearing results after transmastoid superior semicircular canal plugging for superior semicircular canal dehiscence: a meta-analysis. Audiol Res 2023;13:730–40.

77. Zhao YC, Somers T, van Dinther J, Vanspauwen R, Husseman J, Briggs R. Transmastoid repair of superior semicircular canal dehiscence. J Neurol Surg B Skull Base 2012;73:225–9.

78. Yamauchi D, Hara Y, Hidaka H, Kawase T, Katori Y. How I do it: underwater endoscopic ear surgery for plugging in superior canal dehiscence syndrome. J Laryngol Otol 2017;131:745–8.

79. Kawamura Y, Yamauchi D, Kobayashi T, Ikeda R, Kawase T, Katori Y. Hearing outcomes of transmastoid plugging for superior canal dehiscence syndrome by underwater endoscopic surgery: with special reference to transient bone conduction increase in early postoperative period. Otol Neurotol 2022;43:368–75.

80. Vlastarakos PV, Proikas K, Tavoulari E, Kikidis D, Maragoudakis P, Nikolopoulos TP. Efficacy assessment and complications of surgical management for superior semicircular canal dehiscence: a meta-analysis of published interventional studies. Eur Arch Otorhinolaryngol 2009;266:177–86.

81. Gioacchini FM, Alicandri-Ciufelli M, Kaleci S, Scarpa A, Cassandro E, Re M. Outcomes and complications in superior semicircular canal dehiscence surgery: a systematic review. Laryngoscope 2016;126:1218–24.

82. Silverstein H, Kartush JM, Parnes LS, Poe DS, Babu SC, Levenson MJ, et al. Round window reinforcement for superior semicircular canal dehiscence: a retrospective multi-center case series. Am J Otolaryngol 2014;35:286–93.

83. Silverstein H, Kellermeyer B, Martinez U. Minimally invasive surgery for the treatment of hyperacusis: new technique and long term results. Am J Otolaryngol 2020;41:102319

84. Succar EF, Manickam PV, Wing S, Walter J, Greene JS, Azeredo WJ. Round window plugging in the treatment of superior semicircular canal dehiscence. Laryngoscope 2018;128:1445–52.

85. Conway RM, Tu NC, Pinther S, Shareef Z, Hong RS, Zappia JJ, et al. Audiologic outcomes after oval and round window reinforcement surgery. Otol Neurotol 2021;42:1051–7.

86. Palma Diaz M, Cisneros Lesser JC, Vega Alarcón A. Superior semicircular canal dehiscence syndrome - diagnosis and surgical management. Int Arch Otorhinolaryngol 2017;21:195–8.