Vol. 11 • Issue 6
• Page 46
Along with otolaryngologists, pediatric audiologists are involved in the diagnosis of patients with enlarged vestibular aqueduct syndrome (EVA). An enlarged vestibular aqueduct is one of the most commonly identified inner ear bony malformations in children with sensori-neural hearing loss (SNHL) of unknown cause: up to 11 percent of all SNHL and 35 percent of unilateral SNHL.1 Because the syndrome lacks unique characteristics, it may go undetected or undiagnosed until adulthood. As a group, audiologists seem to be minimally aware of EVA, even though we are key players in diagnosis and follow-up care.2
What is EVA?
The vestibular aqueduct (VA) is a small, bony canal bridge that extends from the vestibule to the posterior surface of the petrous portion of the temporal bone. The vestibular aqueduct contains the endolymphatic duct attached to the endolymphatic sac.
EVA involves the congenital malformation of the vestibular aqueduct; usually dilation of the endolymphatic duct and sac are observed as well.3In 1791, Mondini, the Italian physician, first identified these inner ear abnormalities using tomography. In 1978, Valvasorri and Clemis reviewed more than 3000 polytomographs and noted 50 patients with enlarged vestibular aqueducts. It was Valvasorri who actually first coined the term "enlarged vestibular aqueduct syndrome."4Valvassori and Clemis (1978) used a benchmark of 0.4mm-1mm as normal size of the VA and 1.5 millimeters and over for EVA.4The fluid-filled duct and sac are thought to help regulate the concentration of ions in the inner ear, which are needed for initiating the transmission of sound and balance signals from the ear to the brain.3
Causes of EVA
Valvassori and Clemis (1978) found that in 62 percent of EVA cases, there were co-morbid ear malformations.4This suggests a genetic propensity for EVA syndrome. It is often associated with Pendred syndrome (which 10 percent of deaf children have)-an autosomal recessive condition that causes both SNHL and enlargement of the thyroid gland (goiter).5Most children with Pendred syndrome have normal thyroid function despite the enlargement of the organ. Many individuals with Pendred syndrome also have Mondini dysphasia of the cochlea, in which one of the turns of the cochlea is missing. Mutation in the gene SLC26A4 results in symptoms of the syndrome.6Levenson et. al suggested that EVA syndrome should be considered to exist only when EVA is the sole anomaly evident in CT scan or MRI. Those combined with other inner ear abnormalities such as Mondini deformity should be excluded from EVA syndrome.7, 8
Diagnosing EVA
For children with hearing loss and potential EVA, audiologic assessment is often the first step in clinical evaluation. EVA affects both the auditory and vestibular systems, predisposing the affected persons to early onset hearing loss and vestibular disturbance. The clinical picture is usually variable and could be unilateral or bilateral. Hearing loss ranges from mild to profound, from fluctuating, progressive or sudden, often triggered by minor head trauma or barotraumas, and in some patients eventually leads to profound SNHL. Progression is not uniform and even varied from side to side in each patient.3, 8Vestibular disturbances range from mild imbalance to episodic vertigo.
In fact, EVA is reported to be the most common inner ear anomaly in children with permanent HL. Audiometric configurations associated with the syndrome are wide-ranging. They may be sloping down to show better hearing in the low frequencies; rising to show better hearing in high frequencies; or have a flat or cookie-cutter appearance.9 Predominantly, pure tone audiometry reveals SNHL, however a few studies have reported that mixed hearing loss, indicated by air-bone gaps (ABG) in the audiogram, is noted in patients as well. 9, 10
The presence of a conductive component can be misinterpreted and lead to erroneous management. Awareness of the ABG in children with EVA will help clinicians make the correct diagnosis and avoid unnecessary middle ear surgery in an attempt to repair ossicular chain and other middle ear pathologies, as these procedures are destined for failure.9In EVA, an enlarged vestibular aqueduct is usually dilated and easily demonstrated on computer tomography (CT). Magnetic resonance imaging (MRI) will show the actual content of the aqueduct and dilated endolymphatic sac. One or both are recommended when evaluating a child with EVA.
Management of EVA
Hearing impairment during childhood can affect social and emotional development, behavior, attention, and academic achievement. No treatment has proven effective in reducing the hearing loss associated with EVA or slowing its progression. Surgery to drain liquid out of the endolymphatic sac and duct or to remove the endolymphatic sac or duct is not only ineffective in treating enlarged vestibular aqueducts, but also potentially harmful.
Case study
The patient is a 4-year-old female. Prenatal and post-partum history is normal and uncomplicated. Medical and surgical history is unremarkable as well. She is well socialized, participates in dance class and is generally liked by peers.
Both of the patient's parents expressed concern regarding decreased hearing abilities in her left ear. They notice she is turning her right ear towards them in order to hear and has a tendency to say "huh?" or "what?" more often than her peers. Her parents state that her articulation skills are not considered to be age appropriate. She had five ear infections when she was around 3 months to 6 months old but has not had one since. Within the past few months, she has complained of headaches, and her parents have noticed that she seems to have more difficulty with her balance than her peers during dance class. The patient reports that her left ear feels "clogged" all the time.
Otoscopy revealed clear and intact tympanic membrane. Tympanometry revealed normal tympanic membrane movement in the left ear and negative pressure with normal compliance of the tympanic membrane in the right ear. Acoustic reflexes were present ipsilaterally and questionable contralaterally. Comprehensive testing was performed using insert earphones. Speech reception thresholds were present at 10dB HL in her right ear and 65dB HL in her left ear. When presented at normal speech level in her right ear, she repeated 92 percent of monosyllable words, with slight articulation errors noted. In her left ear, she was only able to repeat 78 percent of words correctly when the speech stimuli were presented at 80dBHL. Pure tones thresholds indicated a mild low frequency sloping to a severe high frequency mixed hearing loss in the left ear and mild conductive loss in low frequencies rising to normal thresholds in the mid and high frequencies in the right ear. A recommendation was made that she be retested at another appointment to validate the thresholds since the parents noted the patient was just getting over a cold.
Vestibular Testing
When dealing with vertigo and/or dizziness, many people have difficulty describing their symptoms, so a structured case history and questionnaire is essential to identifying various vestibular disorders. Obtaining a valid case history, however, was difficult as the patient in question was only 4 years old. Because of the parents' concern regarding the patient's balance, several screening tests were performed.
The Romberg test involves having the patient stand with feet shoulder length apart and eyes closed to see if the patient can maintain balance. It tests vestibular (primarily otolith organs) and proprioceptive balance pathways.7In a patient with a normal vestibular system, there should be very little sway. In a patient with an abnormal vestibular system, sway will be excessive. The results in this case were normal.
The Tandem walk test involves having the patient stand with feet placed one in front of the other and then walk from heel to toe. In a patient with a normal vestibular system, they should be able to complete this task with little sway or side stepping; our patient was unable to walk for more than a few steps, suggesting balance might be impaired.
The Halmagyi head thrust involves having a patient rapidly move the head to the right and left while staring at the examiner's nose. In a patient with a normal vestibular system, the eyes should not move away from the nose. Inability to hold steady on the nose, nystagmus or not being able to change back to refocus on the nose would all be positive signs for a patient with an abnormal vestibular system. Abnormal saccadic eye movement on one side indicates ipsilateral weakness.11Test results were normal in our case.
Romberg on foam also was performed. In this test, the vestibulospinal pathway can be isolated by having the patient stand on a foam surface to minimize proprioceptive input, with eyes opened (visual) then closed. In a patient with a normal vestibular system, there should be very little sway. In a patient with an abnormal vestibular system, sway will be excessive. According to Rogers, results do not indicate where the site of lesion is but rather tell what the patient depends on most to maintain their balance.12The test results showed increased sway with eyes closed.
Results and Recommendations
The parents were counseled regarding findings. The right ear appeared to be essentially normal, with a mild conductive component, most likely secondary to the retracted TM. The left ear demonstrated significant mixed hearing loss of unknown etiology. As audiologists, our goal was to diagnose and remediate hearing and balance disorders. The child's pathology needed to be investigated more thoroughly before proceeding with amplification.
The identification of the unilateral hearing loss prompted a recommendation to her pediatrician to complete a complete blood count (CBC) testing to rule out autoimmune disorder and imaging studies specifically of the inter-auditory canal. Due to the age of our patient, a follow-up appointment to confirm thresholds was scheduled.
Three weeks later, she returned for repeat testing. The hearing sensitivity in her right ear had improved and left ear thresholds were consistent with the previous study. This time the test battery included distortion product otoacoustic emissions, which were present in the right ear and absent in the left, as we would expect from the pure tone findings. Tympanometry revealed normal middle ear pressure and compliance bilaterally.
The CT scan results revealed an enlarged left endolymphatic duct and sac, correlating with EVA. The blood work and MRI of the brain were unremarkable.
It is important to realize that a seemingly light knock to the left temporal bone can cause significant decreases in hearing ability in cases of EVA.3Therefore, the following recommendations were made: avoid contact sports that might lead to head injury (i.e. bicycle riding or skiing); wear head protection when engaged in activities that might lead to head injury; and avoid situations that can lead to barotraumas such as scuba diving or extreme, rapid changes in air pressure.3
fter medical clearance was obtained from an otolaryngologist familiar with EVA in children, the patient was fit with a BTE hearing device. As she is enrolling in kindergarten next fall, efforts have been made to provide her with an FM system at the beginning of the school year. During follow-up visits, her parents report that they have noticed an improvement
in hearing abilities and our patient is excited about hearing better. She has had one or two vertiginous episodes lasting for a few hours. Her hearing appears to be stable for the time being. Assessments will continue every 2 to 3 months or sooner should her parents notice any changes in her hearing.
The Audiologist's Role
EVA is a rare pathology that often is not considered by audiologists. Understanding its clinical signs will ensure that proper referrals and recommendations are made. Early identification of the hearing loss associated with this pathology is possibly the best way to reduce its effect. Theoretically, changing activities to reduce head traumas or repeated bumps to the head can delay the progression of the hearing loss. This proactive approach could be beneficial for young children who are still in the stages of language development, as the impact on their education and lifetime communication might be dramatic if progression to a profound hearing loss can be delayed.
Thinking critically, gathering all appropriate information and synthesis of the data are essential to diagnose a very rare case.
References
1. Germiller, J. (2009). Medical Evaluation and Management of Unilateral Hearing Loss. Presentation at the Children's Hospital of Philadelphia.
2. Callison, DM, Horn, KL. (1998). Large Vestibular Aqueduct Syndrome: An Overlooked Etiology for Progressive Childhood Hearing Loss. Journal of the American Academy of Audiology, 9:285-291.
3. Enlarged Vestibular Aqueducts and Childhood Hearing Loss. National Institute on Deafness and Other Communication Disorders. Accessed online, April 2009: www.nidcd.nih.gov/health/hearing/eva.asp.
4. Valvasori, GE, Clemis, JD. (1978). The Large Vestibular Aqueduct Syndrome. Laryngoscope, 88: 723-9.
5. Reardon, W, Coffey, R, Phelps, PD, Luxon, M, Stephens, D, Kendall-Taylor, P, Britton, KE, Grossman, Trembath, R. (1997). Pendred Syndrome: 100 Years of Underascertainment? Quarterly Journal of Medicine, 90, 443-447.
6. Scott, DA, Wang, R, Kreman, TM, Sheffield, VC, Karnishki, LP. (1999). The Pendred Syndrome Gene Encode-iodide Transport Protein. Nature Genetics, 21: 440-443.
7. Levenson, MJ, Parisier, SC, Jacobs, M, Edelstein, DR. (1989). The Large Vestibular Syndrome in Children: A Review of 12 Cases and the Description of a New Clinical Entity. Arch Otolarygnol Head Neck Surg, 115: 54-58.
8. Jackler, RK, De La Cruz, A. (1989). The Large Vestibular Aqueduct Syndrome. Laryngoscope, 1238-1243.
9. Guangwei, Z, Quinton, G, Margaret, AK. (2008). Delineating the Hearing Loss in Children with Enlarged Vestibular Aqueduct. Laryngoscope, 2062-6.
10. Govaerts, PJ, Casselman, J, Daemers, K, De Ceular, G, Somers, T, Offeciers, FE. (1999). Audiological Findings in Large Vestibular Aqueduct Syndrome. Int J Pediatr Otorhinolaryngol, 51:157-164.
11. Schubert, MC, Tusa, RJ, Herdman, SJ, Grine, L. (2004). Optimizing the Sensitivity of the Head Thrust Test for Identifying Vestibular Hypofunction. Phys Therapy, 84:151-158.
12. Jacobson, GP, Shepard, NT. (2007). The Bedside Assessment of the Vestibular System. Plural Publishing, Inc. 63-97.
Tricia Dabrowski, AuD, is director of the Pennsylvania Ear Institute and assistant professor at Salus University George S. Osborne College of Audiology. Bre Myers, AuD, is co-owner of Berks Hearing Professionals and an adjunct professor at Salus University George S. Osborne College of Audiology. Rufina Danilova is an AuD student at Salus University George S. Osborne College of Audiology.
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