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Enlarged Vestibular Aqueduct Syndrome (EVAS) by Hamid, MD, Phd, EE, the Cleveland Hearing & Balance Center, Lyndhurst, OH; and the Vestibular Disorders Association

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Enlarged Vestibular Aqueduct Syndrome (EVAS) by Hamid, MD, Phd, EE, the Cleveland Hearing & Balance Center, Lyndhurst, OH; and the Vestibular Disorders Association TH 5018 NE 15 AVE · PORTLAND, OR 97211 · FAX: (503) 229-8064 · (800) 837-8428 · [email protected] · WWW.VESTIBULAR.ORG Enlarged Vestibular Aqueduct Syndrome (EVAS) By Hamid, MD, PhD, EE, The Cleveland Hearing & Balance Center, Lyndhurst, OH; and the Vestibular Disorders Association Enlarged vestibular aqueduct Vestibular Cochlea Aqueduct Inner ear Endolymphatic sac Enlarged Endolymphatic duct endolymphatic sac Figure: The inner ear as seen from the back of the head, left side (left image). Close-up view of the inner ear comparing a normal (center image) and enlarged (right image) vestibular aqueduct and endolymphatic sac. Adapted by VEDA with permission from the National Institute on Deafness and Other Communication Disorders (NIDCD). The vestibular aqueduct is a tiny, bony they help maintain the volume and ionic canal that extends from the inner ear composition of endolymph necessary for endolymphatic space toward the brain. It transmitting hearing and balance nerve is shielded by one of the densest bones in signals to the brain. the body, the temporal bone, which also houses the sound-sensing cochlea and When a vestibular aqueduct is larger than motion-sensing vestibular organs vital to normal, it is known as a large vestibular our ability to hear and maintain balance. aqueduct (LVA) or by the term used here, Inside the vestibular aqueduct is the enlarged vestibular aqueduct (EVA). endolymphatic duct, a tube that connects Hearing loss or balance symptoms the endolymph (a fluid) in the inner ear associated with an EVA can occur when to the endolymphatic sac. The function of the endolymphatic duct and sac expand the endolymphatic duct and sac is not to fill the larger space (see Figure). When totally understood, but it is believed that EVA is associated with such symptoms, it syndromic hearing loss and thyroid is referred to as EVA syndrome (EVAS). disease. Pendred syndrome occurs in an estimated one-third of all cases of EVA2 Causes and is an autosomal-recessive genetic During fetal development, the vestibular disorder, meaning each parent must be a aqueduct starts out as a wide tube. By genetic carrier. the fifth week it narrows, and by midterm it approaches adult dimension and shape; EVA can be associated with branchio-oto- however, the vestibular aqueduct renal syndrome, which affects the continues to grow and change until a anatomy of the ears, kidney, and neck. child is 3 to 4 years old. As yet incom- Additionally, it can be associated with pletely understood genetic or environ- other anatomical defects such as mental conditions cause EVA, which is a Mondini malformation, an incomplete often congenital (present at birth) or cochlear development that is also linked occurs during early childhood. to a mutation of the PDS gene. Hearing loss associated with EVAS can be Prevalence syndromic deafness, a loss of hearing EVAS is considered to be rare, but as with accompanied by physical signs and many inner ear disorders, its true symptoms affecting other parts of the prevalence is difficult to assess because it body. More commonly, it is nonsyndromic is not always recognized during a medical deafness, affecting only ear function evaluation. Estimates fall between (nonsyndromic deafness accounts for as high as 5% to 15% in pediatric approximately 70% to 80% of all genetic patients.2,3 More women than men are hearing loss1). Just as the cause of EVAS affected; for every two males with EVAS, remains unclear, much of what is known there are three females who have the about it—why the hearing loss pattern disorder. EVAS is associated with differs among patients, how many people vestibular symptoms in a small actually have it, how it causes symptoms, percentage of people.2 how to effectively treat it, and what the prognosis might be—comes from isolated Hearing symptoms clinical observations and small studies, It is hearing loss that usually brings EVAS to not from comprehensive scientific the attention of a physician. Such loss can research. be sensorineural, conductive, or both. Sensorineural hearing loss (SNHL) is Genetic testing often but not always deafness usually related to the cochlea, but reveals that EVA is associated with sometimes to the vestibulocochlear nerve mutation of the SLC26A4 gene (also called or the brain’s central auditory system. Con- the PDS gene) which also causes Pendred ductive hearing loss involves reduced syndrome, a condition associated with movements of the middle ear bones © Vestibular Disorders Association ◦ www.vestibular.org ◦ Page 2 of 7 (malleus, incus, and stapes) which conduct physician may not ask the questions external sound to the inner ear. necessary to discover them. However, these signs and symptoms can also be Some people are born with the hearing seen in other types of vestibular disorders loss. However, in most cases of EVAS, a and are not unique to the diagnosis of child will hear normally in the first years of EVAS. life and then notice hearing loss later in childhood, or less commonly in Traditionally, physicians have devoted adolescence or early adulthood. Generally, more attention and study to the effect of this occurs after a minor or major head EVAS on hearing, but an increasing clinical impact, upper respiratory infection, or air awareness of the impacts of vestibular pressure trauma, such as occurs during dysfunction on childhood development is the rapid depressurization of an airplane. starting to change that. These impacts Even active play, especially jumping, can manifest in outward signs such as reflex jar the head enough to result in hearing delays, visual-spatial problems, motion loss if an EVA is present. The loss can be sensitivity, abnormal movement patterns, progressive, fluctuating, stable, or sudden, clumsiness, difficulty moving in the dark, and can involve tinnitus, a ringing in the and lingering anxiety. Many of childhood’s ears. However, generally the hearing loss common milestones—climbing stairs, occurs in a series of steps. With each riding bicycles—may be delayed, or simply minor event, hearing drops one or more too difficult for a child with EVAS to levels, a downward progression often manage without treatment. It is also culminating in profound hearing loss. important to note that these symptoms can have other causes besides inner ear Vestibular symptoms disorders, which is why a thorough Vestibular symptoms sometimes related to medical evaluation by a pediatrician, EVAS include episodic spinning vertigo, otologist/neurotologist, and neurologist is mild unsteadiness, trouble watching needed. revolving objects, a feeling of vague instability, rocking sensations, jumping How does EVAS cause symptoms? vision, decreased visual acuity in the The SNHL and balance symptoms presence of loud sounds, instability when associated with EVAS may occur because leaning forward, vomiting, nausea, and the enlarged endolymphatic duct and sac drunken gait. A young child may also grab are unable to maintain their normal his or her head and walk in circles. The functions. These include maintaining the symptoms of vestibular disorders are endolymph volume and ionic composition notoriously difficult for children and adults (concentrations of sodium, potassium, to describe; for children, the task is even calcium, and chloride) necessary for more challenging. Unless well trained in transmitting hearing and balance nerve recognizing vestibular disorders, a signals to the brain. This disrupts inner © Vestibular Disorders Association ◦ www.vestibular.org ◦ Page 3 of 7 ear homeostasis, which is ionic equilibrium Audiologic testing often reveals low among the compartments of the inner ear frequency conductive hearing loss, high that contain either endolymph or frequency SNHL, or both. Vestibular tests perilymph, fluids that have specific and may be useful even if a person with EVAS different concentrations of ions. If related is not experiencing active vestibular to head trauma, EVAS may cause symp- symptoms such as vertigo.4 When elec- toms when the sudden fluctuation in cere- tronystagmography (ENG) is used to brospinal fluid (CSF) pressure on impact measure eye movements and vestibular forces highly concentrated (hyperosmolar) responses to thermal (caloric) or rotational proteins into the cochlear duct which stimulation, it may reveal loss of vestibular connects the CSF space to the endolymph function in one or both ears and space inside the cochlea. This is called nystagmus, the abnormal eye movements hyperosmolar reflux. commonly associated with vestibular dysfunction. Conductive hearing loss with EVAS may For radiologic assessment, fast spin-echo occur because the increased magnetic resonance imaging (MRI) is endolymphatic pressure reduces the generally considered to be the most ability of the stapes to move the oval appropriate test5,6 because it permits window, which is the membrane precise imaging and measurement of the separating the middle ear from the fluid- endolymphatic duct and sac soft tissues. filled inner ear. Because of this dysfunc- High resolution computerized tomography tion, sound waves conducted through the (CT) scans of the temporal bone are also middle ear can’t be transferred to often used to confirm the bony enlarge- the cochlea in the inner ear. ment and other bony abnormalities that are often associated with EVAS. No Clinical evaluation standard radiographic criteria exist yet to define what size constitutes an The variable signs of EVAS indicate that enlargement.7 Some studies suggest that a diagnosis requires special care and vestibular aqueduct is enlarged if it is more attention to a person’s symptoms and than 1.5 millimeters (mm) in diameter, medical history, especially those of children. while others define an EVA as being more In addition to a complete medical history than 4.0 mm in size.5 and physical examination, the diagnostic process for uncovering EVAS usually Treatment involves hearing and balance testing and Historically, medical and surgical radiologic assessment. Thyroid, renal, and treatments have not reversed the cardiac function are also usually analyzed, progression of hearing or vestibular losses and genetic screening is sometimes also from an EVA.
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