Anne L. Oyler, MA, CCC-A
Every year 1 to 3 of every 1000 babies is identified with hearing loss through newborn hearing screenings (Finitzo, Albright, & O'Neal, 1998). In the school-age population the prevalence of permanent hearing loss has been estimated to be approximately 10 to 15 per 1000 (Bess, Dodd-Murphy, & Parker, 1998). This increase in prevalence has been linked to factors such as variations in the definition of hearing loss, loss to follow-up after newborn hearing screening, and also to subsequent progressive and late-onset hearing losses, which can have either genetic or environmental causes.
One significant cause of progressive hearing loss is the congenital enlargement of the cochlear aqueducts. This condition is referred to as large vestibular aqueduct (LVA) syndrome, also known as enlarged or dilated vestibular aqueduct syndrome. In 1995, Okumura et. al., identified 13 patients with LVA out of a group of 181 who had sensorineural hearing loss (SNHL) of unknown etiology. Half of the 13 patients with LVA had experienced sudden hearing loss. Similarly, Callison and Horn (1998) found a 5% prevalence of LVA in their clinical population. LVA is generally bilateral and almost always leads to some degree of progressive or fluctuating hearing loss. Hearing loss is often reported following head injury (Smith & Van Camp, 2006). According to the literature, LVA is the most common malformation of the inner ear associated with SNHL (Online Mendelian Inheritance in Man [OMIM], 2007). It can occur in isolation or in combination with other malformations of the cochlea.
The vestibular aqueduct is the bony canal that travels away from the vestibule and into the temporal bone. The aqueduct contains the membranous cochlear duct and terminates in the endolymphatic sac. When the aqueduct is enlarged, the endolymphatic sac and duct tend to enlarge and fill the space. The endolymphatic duct and sac are thought to help regulate the concentration of ions in the cochlear fluids and this enlargement may result in a chemical imbalance. LVA can result from abnormal or delayed development of the inner ear (non-syndromal) or may be associated with syndromes such as Pendred syndrome (PS), brancio-oto-renal syndrome, CHARGE syndrome, or Waardenburg syndrome (Pryor et. al, 2005).
In a recent NIDCD study, approximately one-third of individuals with LVAs were subsequently diagnosed with PS (National Institute on Deafness and Other Communication Disorders [NIDCD], 2007). PS has an autosomal recessive inheritance pattern and results from mutations of the SLC26A4 gene found on Chromosome 7 (Smith & Van Camp, 2006). LVA with or without Mondini malformation is reportedly observed in 80% of individuals affected by PS and is almost always bilateral. Over 50% will present with congenital, severe to profound SNHL. Hearing loss can be fluctuating and is progressive in 15%–20% of the cases. When PS and nonsydromal LVA are considered part of the same disease spectrum, the prevalence of this disorder as an etiology for congenital deafness is 5.5% (Smith & Van Camp, 2006).
LVA is diagnosed through computed tomography (CT) imaging of the temporal bones and magnetic resonance imaging (MRI), which is useful in visualizing the endolymphatic duct and sac. Imaging is often recommended for children with congenital SNHL of unknown origin or those who have experienced a sudden change in hearing. LVA is the most commonly observed radiographic abnormality in children with SNHL (OMIM, 2006).
The progressive nature of hearing loss with LVA is a great concern to patients and their families. Counseling should stress the importance of protecting residual hearing by avoiding activities that could lead to head injury (e.g. high impact sports) or barotrauma (scuba diving) and wearing protective head gear while engaging in potentially dangerous activities such as bike riding, skateboarding, or skiing. Because hearing loss often progresses to the severe to profound range, it is important that hearing be monitored frequently. This is especially important in infants and toddlers who cannot convey that a change in their hearing has occurred. Careful fitting and close monitoring of amplification is also imperative due to the fluctuating and progressive nature of hearing loss. Finally, families should be educated regarding the potential for complete loss of hearing and provided with information regarding communication methodologies and cochlear implants so that they can make informed decisions when necessary.
NIH is currently recruiting patients with SNHL and their families for a study titled " Clinical and Molecular Analysis of Enlarged Vestibular Aqueducts."
Large Vestibular Aqueduct Syndrome
Dr. J. G. Neely, Director of Otology/Neurotology/Base of Skull Surgery.
Large Vestibular Aqueduct Syndrome
Noel Cohen, MD, Mendik Foundation Professor of Otolaryngology and Chairman, Departments of Otolaryngology and Administration, New York University Medical Center (February 18, 2002).
Unilateral Hearing Impairment in Children: Age of Diagnosis
Melissa N. Ruscetta, MA and Ellis M. Arjmand, MD, PhD. (June 9, 2003).
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