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Enlarged Vestibular Aqueduct Syndrome

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Enlarged Vestibular Aqueduct Syndrome Enlarged vestibular aqueduct Vestibular Cochlea Aqueduct Inner ear Endolymphatic sac Enlarged Endolymphatic duct endolymphatic sac Figure 1: (L) The inner ear as seen from the back of the head, left side. Close-up view of the inner ear comparing a normal (center) and enlarged (right) vestibular aqueduct and endolymphatic sac. Source: National Institute on Deafness and Other Communication Disorders (NIDCD). The vestibular aqueduct is a tiny, bony composition of endolymph necessary for canal that extends from the inner ear’s transmitting hearing and balance nerve endolymphatic space toward the brain. It signals to the brain. is shielded by one of the densest bones in the body, the temporal bone, which also When a vestibular aqueduct is larger than houses two sensory organs - the cochlea, normal (>1.0-1.5 mm), it is known as a which detects sound waves and turns large vestibular aqueduct (LVA) or by the them into nerve signals, which are then term used here, enlarged vestibular sent to the brain, and the vestibular aqueduct (EVA). EVA is the most common labyrinth, which detects movement and inner ear malformation associated with gravity. Inside the vestibular aqueduct is sensory hearing loss, and is detected with the endolymphatic duct, a tube which a CT scan. Hearing loss or balance carries endolymph to the endolymphatic symptoms associated with an EVA can sac, which is housed on the posterior occur when the endolymphatic duct and surface of the temporal bone and sac expand to fill the larger space (see contacts the dura mater. The function of Figure 1). When EVA is associated with the endolymphatic duct and sac is not such symptoms, it is referred to as EVA totally understood, but it is believed that syndrome (EVA). they help maintain the volume and ionic e.g. why the hearing loss pattern differs During fetal development, the vestibular among patients, how many people aqueduct starts out as a wide tube. By actually have it, how it causes symptoms, the fifth week it narrows, and by midterm how to effectively treat it, and what the it approaches adult dimension and shape. prognosis might be, remains under However, the vestibular aqueduct investigation. continues to grow and change until a Genetic testing often but not always child is three to four years old. As yet reveals that EVA is associated with incompletely understood genetic and/or mutation of the SLC26A4 gene (also called environmental conditions cause EVA. It the PDS gene) which also causes Pendred is clear that EVA is a congenital syndrome, a condition associated with malformation, however, controversies syndromic hearing loss and thyroid exist on its origins, with two prevalent disease. Pendred syndrome occurs in an theories: estimated one-third of people who have 1. EVA is caused by arrested EVA2 and hearing loss. Hearing loss development in early gestation, or associated with Pendred syndrome is 2. EVA results from aberrant usually progressive. development later in fetal and postnatal life. EVA can also be associated with branchiootorenal syndrome, which affects It is believed that an EVA does not cause the anatomy of the ears, kidney, and hearing loss, but rather that both are neck. caused by the same underlying defect – i.e. mutations in a gene which causes EVA is often associated with other inner syndromic and non-syndromic hearing ear malformations, such as a Mondini loss. malformation, an incomplete cochlear development that is also linked to a Hearing loss can be conductive, mixed or mutation of the PDS gene. sensorineural, and the loss may be stable or fluctuating. Examples of syndromic EVA include Pendred syndrome or branchiootorenal syndrome. Syndromic The true prevalence of EVA is likely hearing loss associated with EVA can underestimated, as with many inner ear affect other areas of the body. More disorders, as it is not always recognized commonly, the hearing loss associated during a medical evaluation. Estimates fall with EVA is nonsyndromic, affecting only between as high as 5% to 15% in ear function. pediatric patients. Some research claims a slight female preponderance. EVA is also Just as the cause(s) of EVA remain associated with vestibular symptoms in unclear, much of what is known about it, some people. © Vestibular Disorders Association ◦ vestibular.org ◦ Page 2 of 6 disorders are notoriously difficult for adults to describe; for children, the task is even more challenging. Unless well trained in It is hearing loss that usually brings EVA to recognizing vestibular disorders, a the attention of a physician. Hearing loss can physician or audiologist may not ask the be sensorineural, conductive, or both. questions necessary to identify the patient’s vestibular problem. Sensorineural hearing loss (SNHL) is usually related to the cochlea, but sometimes to the Physicians and researchers have vestibulocochlear nerve or the brain’s central traditionally devoted more attention and auditory system. Conductive hearing loss study to the effect of EVA on hearing than involves a problem conducting sound waves on the vestibular system. However, there anywhere along the route through the outer is an increasing awareness of the impacts ear, tympanic membrane (ear drum) or of vestibular dysfunction on persons middle ear (ossicles). diagnosed with EVA. Vestibular hypofunction is frequent, with other Some people with EVA are born with the otologic symptoms variable and hearing loss. However, in most cases of nonspecific, such as tinnitus and aural EVA, the hearing loss is sudden and often fullness. Recently, EVA has been progressive. It may also appear in associated with benign paroxysmal adolescence or early adulthood. Generally, positional vertigo (BPPV) as well as this occurs after a minor or major head endolymphatic hydrops. Recent research impact, upper respiratory infection, or air has reported that vestibular dysfunction in pressure trauma such as occurs during the persons with EVA is not uncommon. An rapid depressurization of an airplane. The increased number of vestibular signs and loss is often fluctuant and progressive, but symptoms are correlated with bilateral generally the hearing loss occurs in a EVA. It must also be noted that not all series of steps. The hearing loss onset or patients with vestibular signs and diagnosis is almost always in childhood. In symptoms have abnormal vestibular test patients with EVA, the hearing loss is results, and vice versa (a person with EVA usually bilateral (in both ears) but not may have abnormal vestibular test results symmetrical. but not report symptoms). Physicians and audiologists should be aware of the prevalence of vestibular disorders in Vestibular symptoms are not as common patients with EVA. as hearing loss in persons with EVA. Symptoms range from severe episodic vertigo to unsteadiness (usually in adults) to poor coordination and imbalance in children.The symptoms of vestibular © Vestibular Disorders Association ◦ vestibular.org ◦ Page 3 of 6 The sensorineural hearing loss and person’s symptoms and medical history, balance symptoms associated with EVA especially for children. In addition to a may occur because the enlarged complete medical history and physical endolymphatic duct and sac are unable to examination, the diagnostic process for maintain their normal functions. These uncovering EVA usually involves audiologic include maintaining the endolymph and vestibular testing as well as radiologic volume and ionic composition assessment. Diagnosis is usually done by (concentrations of sodium, potassium, positively identifying EVA on a CT-scan, or calcium, and chloride) necessary for confirming an enlarged endolymphatic duct transmitting hearing and balance nerve and sac on high-resolution MRI. Thyroid, signals to the brain. This disrupts inner renal, and cardiac function may also be ear homeostasis, the ionic equilibrium analyzed, and genetic screening is among the compartments of the inner ear sometimes also performed. that contain either endolymph or perilymph, fluids that have specific and different concentrations of ions. Historically, medical and surgical treatments have not reversed the If related to head trauma, EVA may cause progression of hearing or vestibular losses symptoms when the sudden fluctuation in from an EVA. Steroid use for sudden cerebrospinal fluid (CSF) pressure forces hearing loss associated with EVA has not highly concentrated proteins into the proven effective. Surgical shunting or cochlear duct, which connects the CSF removal of the endolymphatic sac is space to the endolymph space inside the harmful and not considered a treatment cochlea. This is called hyperosmolar option. reflux. There is no cure for EVA, but early Conductive hearing loss with EVA may diagnosis and prevention from (further) occur due to increased endolymphatic head trauma is necessary. People with pressure. This pressure reduces the ability EVA are cautioned to avoid contact sports of the stapes to move the oval window, and wear a helmet while bicycling or which is the membrane separating the performing other activities that elevate middle ear from the fluid-filled inner ear. risk of head injury. Because of this dysfunction, sound waves conducted through the middle ear can’t be Amplification in the form of hearing aids transferred to the cochlea in the inner ear. can be helpful. In the case of fluctuating or progressive hearing loss, hearing aids with flexible programming options are necessary. Cochlear implants have also Due to the variable signs of EVA, diagnosis proven to be beneficial in some patients requires special care and attention to a with EVA (this will depend on the © Vestibular Disorders Association ◦ vestibular.org ◦ Page 4 of 6 existence of any co-morbid inner ear Evidence-Based Treatment anomalies). In those persons with related vestibular symptoms, treatment may References include vestibular rehabilitation therapy. 1. US National Library of Medicine. “Nonsyn- dromic deafness.” Available at: http://ghr.nlm.nih.gov/condition= Predicting what will ultimately happen in nonsyndromicdeafness. Accessed December 14, any one case of EVA is difficult because 2009. the condition follows no typical course. 2.
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