Enlarged vestibular aqueduct
Enlarged vestibular aqueduct syndrome
Description, Causes and Risk Factors:
Enlarged vestibular aqueduct is the most common form of congenital inner ear abnormality seen on radiologic assessment. The prevalence of enlarged vestibular aqueduct syndrome has been estimated to range from 1-12% in population with sensorineural hearing loss.
The vestibular aqueduct is a tiny, boney canal that extends from the inner ear endolymphatic space toward the brain. It is shielded by one of the dense bones in the body, the temporal bone, which also houses the sound-sensing cochlea and motion-sensing vestibular organs to our ability to hearing and maintain balance. Inside the vestibular aqueduct is the endolymphatic duct, a tube that connects the endolymph in the inner ear to the endolymphatic sac. The function of the endolymphatic duct and sac is not totally understood, but it is believed that they help maintain the volume of ionic composition of the endolymph necessary for transmitting hearing and balance nerve signals to the brain. When the vestibular aqueduct is larger than normal, it is known as an enlarged vestibular aqueduct.
EVA is characterized by the presence of an abnormally large vestibular aqueduct (LVA) generally associated with fluctuating, progressive sensorineural hearing loss (SNHL), often enlarged vestibular aqueduct has many causes, not all of which are fully understood. The most well-known cause of EVA and hearing loss is mutations to a gene known as SLC26A4 (also referred to as the PDS gene) on chromosome 7. Two mutations in the PDS gene can result in Pendred syndrome. Scientists believe that other, currently unknown genetic or environmental factors also may result in EVA.
Risk factors may include:
Family history of hearing loss.
NICU stay > 5 days.
Certain syndromes and associated physical findings.
EVA was seen in 50% of children with unilateral hearing loss (6/12) versus 18.8% (16/85) of children with bilateral hearing loss. EVA is reportedly twice as likely to cause bilateral than unilateral hearing loss.
Typical enlarged vestibular aqueduct syndrome has the association of congenital bilateral neurosensory deafness, thyroid goiter, cochleovestibular malformation and potential vestibular dysfunction. The severity of the symptoms and the age of onset vary from case to case. Deafness often appears at birth, but it may develop in late infancy or early childhood. Sometimes, deafness is asymmetrical or fluctuant and often it is progressive. Abnormal bones of the inner ear can be observed in enlarged vestibular aqueduct syndrome. Thyroid status varies from euthyroid (goiter) to hypothyroidism. Goiter is secondary to abnormal iodine transport across the thyrocyte and it develops most commonly during adolescence.
The variable signs of EVA indicate that diagnosis requires special care and attention to person's symptoms and medical history, especially those of children. In addition to a complete medical history and physical examination, the diagnostic process of uncovering EVAS usually involves hearing and balance testing and radiologic assessment. Thyroid, renal, and cardiac function are also usually analyzed, and genetic testing is sometimes also performed.
Medical professionals use different clues to help themdetermine the cause of an individual's hearing loss.Two tests that are often used to identify the cause ofhearing loss are magnetic resonance imaging (MRI)and computed tomography (CT) imaging of a person'sinner ear. One or both tests are often recommendedto evaluate a child with sensorineural hearing loss. Thisis particularly true when a child's hearing loss occurssuddenly, is greater in one ear than the other, or variesor gets worse over time. Although most CT scans ofchildren with hearing loss are normal, EVA is the mostcommonly observed abnormality.
Currently, the cornerstone of EVA management is prevention, primarily by protecting the head from trauma that will worsen the progression of symptoms. People with EVA are advised to avoid head blows and contact sports. No treatments can reverse or stop the progression of hearing and/or vestibular losses from EVA. Hearing aids or cochlear implantation may help. Vestibular rehabilitation therapy might also be helpful for managing imbalance and dizziness resulting from an enlarged vestibular aqueduct.
Although some otolaryngologists (a specialist in the disorders of the ear, nose or throat) recommend steroids to treat sudden sensorineural hearing loss, there are no scientific studies to show that this treatment is effective or ineffective when an individual also has EVA. In addition, surgery to either drain liquid out of the endolymphatic sac and duct or to remove the endolymphatic sac and duct is not only ineffective in treating EVA, it can be harmful. Research has shown conclusively that these surgeries can destroy hearing.
Identifying hearing loss as early as possible is the best way to reduce its effect. The earlier hearing loss is identified in children, the sooner they can develop the skills that will help them learn and communicate with others. Children with permanent and progressive hearing loss, which often is linked with EVA, will benefit from learning other forms of communication, such as sign language or cued speech, or using assistive devices, such as a hearing aid or cochlear implant.
NOTE: The above information is educational purpose. The information provided herein should not be used during any medical emergency or for the diagnosis or treatment of any medical condition.
DISCLAIMER: This information should not substitute for seeking responsible, professional medical care.
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