Third Window Disorders
Author Credentials
Matthew Kircher, MD
Assistant Professor
Otology, Neurotology and Skull Base Surgery
Department of Otolaryngology – Head & Neck Surgery
Loyola University Medical Center
Maywood, IL 60153
mkircher@lumc.edu
Module Summary
Third window disorders are acquired or congenital bony defects of the inner ear that allow abnormal communication with the perilymphatic space. Vestibular and auditory symptoms result from a change in the balance between inner ear and middle ear transmitted pressures. Semicircular canal dehiscence, enlarged vestibular aqueduct and cholesteatoma perilymphatic fistula are just a few of the lesions that manifest third window inner ear phenomenon. High-resolution CT scanning is critical for diagnosis, and treatment options vary depending upon patient specific characteristics.
Module Learning Objectives
- Review the signs and symptoms of third window inner ear disorders.
- Explain the pathophysiology underlying third window disorders.
- Describe the role of hearing aids in management of third window disorders.
- Identify the indications for surgical intervention in patients with third window disorders.
- Recognize the advantages, disadvantages, and risks of surgical techniques in the management of third window disorders.
Topics
Embryology
Learning Objectives
- Recognize that third window disorders can be congenital or acquired.
- Recognize that various inner ear malformations may result from embryologic developmental arrest at any stage, with the type of malformation depending on the gestational age at which the arrest occurs.
- Explain that the most common congenital third window abnormality is an enlarged vestibular aqueduct.
References
- Jackler RK, Luxford WM, House WF. Congenital malformations of the inner ear: a classification based on embryogenesis. Laryngoscope 1987;97(3 Pt 2, Suppl 40):2–14.
- Sennaroglu L, Saatci I. A new classification for cochleovestibular malformations. Laryngoscope 2002;112:2230–41.
Anatomy
Learning Objectives
- Identify that third window anatomic defects include:
- Semicircular canal dehiscence
- Perilabyrinthine fistula
- Enlarged vestibular aqueduct
- Dehiscence of the scala vestibuli side of the cochlea
- X-linked stapes gusher
- Bone dyscrasias
References
- Minor LB, Solomon D, Zinreich JS, et al. Sound- and/or pressure-induced vertigo due to bone dehiscence of the superior semicircular canal. Arch Otolaryngol Head Neck Surg 1998;124:249-58.
- Merchant SN, Rosowski JJ. Conductive hearing loss caused by third-window lesions of the inner ear. Otol Neurotol 2008; 29:282–89.
- 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.
Pathogenesis
Learning Objectives
- State that third window abnormalities are inner ear hydrodynamic phenomena resulting from various defects in the bony structure of the inner ear.
- Realize that normal sound conduction is transmitted through the oval and round windows, which serve as interfaces between the middle ear and perilymphatic fluid.
- Report that with air conduction; incoming acoustic energy is shunted away from the cochlea through the third window resulting in reduced acoustic energy delivered to the hair cells and conductive hearing loss.
- Explain that with bone conduction; otic capsule vibration and differences in impedance at the oval and round windows allow for a pressure gradient across the basilar membrane creating the perception of sound. The presence of a third window communicating with the scala vestibuli lowers the oval window impedance, increases gradient across the basilar membrane, and thereby improves bone-conducted sound perception (bone thresholds are supra-normal).
- Cite that the potential causes of perilabyrinthine fistula include:
- Cholesteatoma
- Trauma
- latrogenic injury
- Neoplasm
- List that the congenital third window defects include:
- Enlarged vestibular aqueduct
- Dehiscence of the scala vestibuli side of the cochlea
- X-linked stapes gusher
- Discuss that superior semicircular canal dehiscence (SSCD) is thought to develop in situations of congenitally thin bone, and in some cases attributed to trauma or intracranial hypertension.
- Understand that bone dyscrasias can incite pathologic bone turnover with osteoclastic activation, and the affected bone demonstrates decreased acoustic impedance acting as a mechanically distributed third window.
- Otosclerosis
- Osteogenesis Imperfecta
- Fibrous Dysplasia
- Paget's Disease
- Primary and Secondary Hyperparathyroidism
- Disseminated Syphilis
- Tuberculosis
References
- Merchant SN, Rosowski JJ. Conductive hearing loss caused by third-window lesions of the inner ear. Otol Neurotol 2008;29:282–89.
- 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.
- Ikeda R, Kobayashi T, Kawase T, et al. Risk factors for deterioration of bone conduction hearing in cases of labyrinthine fistula caused by middle ear cholesteatoma. Ann Otol Rhinol Laryngol 2012;121: 162–67.
- Ho, M. Third Window Lesions. Neuroimag Clin N Am 29 (2019) 57–92.
- Ward BK, Carey JP, Minor LB. Superior Canal Dehiscence Syndrome: Lessons from the First 20 Years. Front Neurol. 2017;8:177. Published 2017 Apr 28. doi:10.3389/fneur.2017.00177
Incidence
Learning Objectives
- Review that prevalence estimates of third window disorders will vary depending upon the population being studied.
- Cite that among congenital third window disorders, enlarged vestibular aqueduct is the most common entity.
- Recognize the incidence and prevalence of anatomic SSCD and realize that anatomic defect does not always result in SSCD syndrome and it's described signs and symptoms.
- Explain that the most common site of perilabyrinthine fistula in cholesteatoma is the lateral semicircular canal.
References
- Carey JP, Minor L B, Nager GT: Dehiscence or thinning of bone overlying the superior semicircular canal in a temporal bone survey. Arch Otolaryngol Head Neck Surg 126:137-147, 2000.
- Benjamin T. Crane, John P. Carey, and Lloyd B. Minor. Superior Semicircular Canal Dehiscence Syndrome. Otologic Surgery, 2010; eds. Brackmann D, Shelton C, Arriaga M. 3rd ed. Philadelphia: Saunders.
- Ikeda R, Kobayashi T, Kawase T, et al. Risk factors for deterioration of bone conduction hearing in cases of labyrinthine fistula caused by middle ear cholesteatoma. Ann Otol Rhinol Laryngol 2012;121: 162–67.
Genetics
Learning Objectives
- Distinguish that an enlarged vestibular aqueduct is frequently bilateral and may be isolated or associated with a number of other genetic syndromes including:
- Pendred syndrome
- CHARGE syndrome
- Branchio-oto-renal syndrome
- Tell that X-linked stapes gusher is a congenital disorder resulting from a loss-of-function mutation in the POU3F4 gene at the DFN3 locus of the X chromosome.
- Know that X-linked stapes gusher patients are almost exclusively male and present with mixed hearing loss at birth, rapidly progressing to severe deafness in the first decade.
References
- Berrettini S, Forli F, Bogazzi F, et al. Large vestibular aqueduct syndrome:audiological, radiological, clinical and genetic features. Am J Otolaryngol 2005;26:363-71.
- Friedman RA, Bykhovskaya Y, Tu G, et al. Molecular analysis of the POU3F4 gene in patients with clinical and radiographic evidence of X-linked mixed deafness with perilymphatic gusher. Ann Otol Rhinol Laryngol1997;106:320–25.
Patient Evaluation
Learning Objectives
- Identify that history taking is an important first step in patient assessment focusing on:
- Onset, duration, severity, and progression of symptoms
- Family history
- Trauma history
- Exacerbating/alleviating factors
- Recognize the importance of otologic exam, microscopic or endoscopic
- Destructive middle ear processes, such as cholesteatoma can be readily identified on examination
- Identify that evoked eye movements in the plane of the affected canal are the hallmark of semicircular canal dehiscence including:
- Superior and posterior semicircular canal dehiscence
- Lateral semicircular canal fistula associated with cholesteatoma
- Discuss that third window abnormalities can produce sound or pressure induced vertigo, Tullio and Hennebert signs, respectively.
References
- Chien WW, Carey JP, Minor LB. Canal dehiscence. Curr Opin Neurol. 2011 Feb; 24(1):25-31.
- Hakuba N, Hato N, Shinomori Y, et al. Labyrinthine fistula as a late complication of middle ear surgery using the canal wall down technique. Otol Neurotol 2002; 23:832–835.
- Zhang Y.B., Dai C.F., and Sha Y.: Sound-induced vertigo due to bone dehiscence of the lateral semicircular canal. Eur Arch Otorhinolaryngol. 2010 Aug;267(8):1319-21.
Measurement of Functional Status
Learning Objectives
Audiometry and Vestibular Testing:
- Explain that a complex and variable pattern of hearing loss can be seen in third window disorders.
- Discuss that third window abnormalities can produce low-frequency air-bone gaps on audiometry.
- In SSCD syndrome, characteristic low frequency air-bone gap results from increased bone and decreased air conduction.
- In cholesteatoma, characteristic air-bone gap at both high and low frequencies results from middle ear involvement.
- Remember that classic hearing loss patterns may be masked by underlying sensorineural or conductive hearing changes.
- Recall that tympanometry and acoustic reflexes may also be utilized to analyze middle ear pathology.
- Recognize that vestibular-evoked myogenic potential testing may show abnormally low response thresholds on the side of pathology.
References
1. Ho, M. Third Window Lesions. Neuroimag Clin N Am 2019 Feb;29(1):57-92.
Imaging
Learning Objectives
- Explain that high resolution computed tomography of the temporal bone with multiplanar reconstructions and reformats parallel to (Pöschl plane) and perpendicular to (Stenvers plane) the canal are used to demonstrate SSCD.
- Recognize that several classification schemes have been proposed for the diagnosis of enlarged vestibular aqueduct (EVA), but in practice, the adjacent inferior limb of posterior semicircular canal serves as an approximate reference to compare the size of the vestibular aqueduct.
- Discuss that incomplete partition type II, formerly known as Mondini triad, is the most characteristic malformation with EVA and includes:
- “Baseball cap” cochlea with bulbous nonseparation of the middle and apical turns
- Enlarged vestibule with normal semicircular canals
- Dilated vestibular aqueduct and endolymphatic sac
- Realize that imaging of x-linked stapes gusher, also known as incomplete partition type III, reveals:
- “Corkscrew” cochlea with bulbous turns
- Absent modiolus
- Patulous cochlear aperture
- Deficient bony lamina cribrosa, which normally separates the basal turn of cochlea from internal auditory canal fundus
References
- Sequeira SM, Whiting BR, Shimony JS, et al. Accuracy of computed tomography detection of superior canal dehiscence. Otol Neurotol 2011;32:1500–05.
- Boston M, Halsted M, Meinzen-Derr J, et al. The large vestibular aqueduct: a new definition based on audiologic and computed tomography correlation. Otolaryngol Head Neck Surg 2007;136(6): 972–7.
- Valvassori G, Clemis J. The large vestibular aqueduct syndrome. Laryngoscope 1978;88:273–8.
- Ho, M. Third Window Lesions. Neuroimag Clin N Am 2019 Feb;29(1):57-92.
- Sennaroglu L, Saatci I. A new classification for cochleovestibular malformations. Laryngoscope 2002;112:2230–41.
Pathology
Learning Objectives
- Understand that an infectious and/or inflammatory process underlies labyrinthine fistula in cases of chronic otitis media with or without cholesteatoma.
References
- Jang CH, Merchant SN. Histopathology of labyrinthine fistulae in chronic otitis media with clinical implications. Am J Otol 1997;18(1):15–25.
Treatment
Learning Objectives
- Understand that the treatment of third window disorders is patient specific.
References
Ho, M. Third Window Lesions. Neuroimag Clin N Am 29 (2019) 57–92.
Medical Therapies
Learning Objectives
- Distinguish that some patients will benefit from hearing aids depending on type and severity of hearing loss.
- Recognize the need for counseling on patient safety in avoidance of triggers for sound and pressure induced vertigo.
- Cite that it is controversial on whether to recommend avoidance of contact sports for patients with EVA.
- Report that bisphosphonates and dietary supplements can be used to promote otic capsule mineralization.
References
- Ho, M. Third Window Lesions. Neuroimag Clin N Am 29 (2019) 57–92.
- Brodsky JR, Choi SS. Should children with an enlarged vestibular aqueduct be restricted from playing contact sports? Laryngoscope 2018 Oct;128(10):2219-2220.
Surgical Therapies
Learning Objectives
- Explain that indications for surgery in third window disorders are varied and dependent upon patient specific factors.
- Review that surgical repair options for SSCD include:
- Resurfacing, capping, or plugging of the involved canal
- Discuss that management of cholesteatoma with labyrinthine fistula may either involve:
- Removal of matrix with exposure and repair of fistula
- Carries risk of inner ear damage
- Maintenance of matrix on fistula to avoid exposure and risk
- Requires long-term cavity maintenance
- Appreciate that some patients will benefit from cochlear implantation.
- Realize that risks inherent to stapes surgery are increased in x-linked stapes gusher.
References
- Brackmann D, Shelton C, Arriaga MA. Otologic Surgery, Brackman 4th ed.
- Kitahara T, Kamakura T, Ohta Y, et al. Chronic otitis media with cholesteatoma with canal fistula and bone conduction threshold after tympanoplasty with mastoidectomy. Otol Neurotol 2014;35(6): 981–8.
Rehabilitation
Learning Objectives
- Realize that some patients with third window disorders may benefit from vestibular therapy.
References
- Hall CD, Herdman SJ, Whitney SL, et al. Vestibular Rehabilitation for Peripheral Vestibular Hypofunction: An Evidence-Based Clinical Practice Guideline: FROM THE AMERICAN PHYSICAL THERAPY ASSOCIATION NEUROLOGY SECTION. J Neurol Phys Ther. 2016;40(2):124-55.
Review
Review Questions
- What factors on history are important to elicit in a patient with third window disorders?
- What are some expected findings on audiometry and vestibular testing in third window disorders?
- What is the appropriate imaging modality to assess a suspected inner ear third window?
Resources