Volume 1, Issue 2 , Pages 142-144, June 2006
Enlarged vestibular aqueduct syndrome: A case of bilateral, sudden sensorineural hearing loss in a child☆
Article Outline
Summary
Enlarged vestibular aqueduct syndrome (EVAS) is defined as progressive, fluctuating sensorineural hearing loss with radiologic evidence of large vestibular aqueducts. Since its first description multiple articles have illustrated the epidemiology, proposed mechanisms of altered inner ear development, and its association with sensorineural hearing loss. We describe for the first time in the English literature a child who experienced sudden onset of bilateral, sensorineural hearing loss after minor head trauma. There is no medical or surgical treatment for this condition, but amplification with hearing aids and cochlear implantation are viable options for patients.
Keywords: Large vestibular aqueduct syndrome, Enlarged vestibular aqueduct syndrome, Sudden hearing loss, Sensorineural hearing loss
1. Introduction
Large vestibular aqueduct syndrome (LVAS) was first described in 1978 by Valvassori and Clemis in their radiographic review of 3700 cases [1]. Large vestibular aqueduct syndrome (LVAS) or enlarged vestibular aqueduct syndrome (EVAS) is characterized by sensorineural hearing loss with radiologic findings of a large vestibular aqueduct or endolymphatic duct and sac. EVAS is most commonly associated with other inner ear anomalies such as an enlarged vestibule or semicircular canals. A finding of isolated enlarged vestibular aqueduct without other inner ear anomalies is argued by some to be a separate entity, but most published reports include cases of isolated large vestibular aqueducts in the EVAS category. We present the first reported case of sudden onset, bilateral sensorineural hearing loss due to EVAS.
2. Case report
A 4-year-old girl was referred to our tertiary care center for sudden onset, bilateral hearing loss. The patient was in otherwise good health, meeting developmental milestones, and without congenital craniofacial anomalies. She was born at term without prenatal or delivery complications. She had multiple episodes of recurrent acute otitis media that required tympanostomy tubes at age two, and then a second set with adenoidectomy less than a year prior to presentation. There was no family history of hearing loss. Upon further questioning the patient's mother revealed concern about some decreased hearing within the past year. Formal audiology workup 6 months prior to presentation demonstrated moderate bilateral sensorineural hearing loss, but there was no documented follow up. There was no reported family history of hearing loss. The patient's 6-month-old brother had a normal newborn hearing screen.
Five days prior to evaluation the patient had fallen from a chair on to the occipital region of her skull. There was no loss of consciousness, vertigo, or hearing complaints. Her parents reported normal behavior within minutes of this relatively minor head trauma. The next morning, approximately 15
h after hitting her head, the patient reported that she could not hear her mother. Upon physician examination the patient had a normal head, neck, and neurological exam and there was no evidence of otorrhea, rhinorrhea, or hemotympanum. CT scan of her head did not reveal intracerebral hemorrhage or temporal bone fracture. She was referred to a local otolaryngologist and audiologist for evaluation. Initial audiogram demonstrated a profound bilateral sensorineural hearing loss. The patient was started on oral steroids and an MRI was carried out without significant reported findings. She was then referred to our institution for evaluation.
Otologic and gross vestibular examination was normal. A repeat audiogram revealed an unchanged, bilateral, profound sensorineural loss. ABR did not demonstrate any response below 80dB bilaterally. Dedicated CT scan of the temporal bones revealed bilateral enlarged vestibular aqueducts without evidence of other inner ear abnormalities (Figs. 1 and 2). The parents were counseled on EVAS and the patient and her sibling were referred to a developmental pediatrician for evaluation and genetic testing. She was fitted with hearing aids and has achieved an aided hearing level of 30dB bilaterally.
Figs. 1 and 2.
Axial CT scan of right (Fig. 1) and left (Fig. 2) temporal bones. Bilateral enlarged vestibular aqueducts demonstrated. Although not shown here, patient had no other inner ear abnormalities identified.
3. Discussion
In Valvassori and Clemis’ original radiographic review of 3700 inner ear anomaly [1] cases they found that 1.5% (50/3700) of patients had an enlarged vestibular aqueduct. Bilateral involvement was twice as common, females outnumbered males 2:1, and association with other inner ear anomalies was found in 60%. In their description an aqueduct was considered enlarged when its anteroposterior diameter measured more than 1.5mm at the midpoint of the post-isthmic segment or halfway between the external aperture and common crus. Since their original description the incidence of large vestibular aqueducts has been documented to range between 0.5 and 1% of the population, and it most likely causes 1.5–10% of sensory hearing loss in children and adolescents [2], [3].
The vestibular aqueduct is a bony canal that travels from the medial wall of the vestibule and traverses the otic capsule to reach the posterior surface of the petrous bone. Its first portion follows in the same direction of the crus commune then it bends to continue its course on under the cerebellar surface of the petrous pyramid [4]. It contains the membranous endolymphatic duct. The vestibular aqueduct shares the same developmental primordium as the cochlea and semicircular canals, thus, an enlarged aqueduct is commonly seen with other cochlear deformities such as aplasia, hypoplasia, and Mondini's deformity [5]. Early in development the endolymphatic duct is short and proportionally wider than at maturity. An insult to its development early in fetal life prevents it from achieving its more elongated, narrow, adult form. Although the exact mechanism of why hearing loss occurs has not been determined, it has been proposed that the lack of complete duct development leads to mixing of endolymph and perilymph causing hearing loss [5], [6]. Another proposed mechanism is that reflux of hyperosmolar endolymph from the endolymphatic sac damages the cochlea. There have been previous reports of autosomal recessive or X-linked familial inheritance of EVAS [7], [8]. In fact, the gene responsible for the sensorineural hearing loss in EVAS, 7q31, overlaps the gene responsible for Pendred's syndrome [9], [10], [11]. Moreover, there is likely a correlation between EVAS and branchio-oto-renal syndrome [12].
Children with hearing loss due to large vestibular aqueducts typically present with a progressive, high frequency, sensorineural hearing loss at an early age. Complaints of vertigo are rare. They are at increased risk of sudden hearing loss as small intracranial pressure changes such as head trauma, air travel, or Valsalva maneuver result in membranous distention [6], [7]. Our patient most likely had the beginning of a progressive hearing loss as an audiogram 1 year previously revealed moderate sensorineural loss. The relatively minor head trauma from a fall of less than 18in. resulted in her bilateral profound loss.
Surgical treatment of LVAS to include shunts and obliteration has not been successful. In the past 10 years cochlear implantation has been used in several patients with successful results. Seven different reports with a total of thirty-seven patients have been published. Upon creation of the cochleostomy CSF leak occurred in 50% of the cases, but all were controlled intraoperatively with muscle packing. There were no significant post-operative complications, and all patients had documented improved speech perception and recognition [3].
Counseling parents of children with large vestibular aqueducts should include discussions on avoiding head trauma, routine audiologic follow up, and screening of other siblings. It is difficult to remove the risk of even the slightest head trauma in children, but they should avoid contact sports, activities that involve heavy lifting, and endeavors where there are barometric pressure changes such as SCUBA diving. The natural course will most likely result in progressive bilateral severe to profound hearing loss. Referral to a developmental pediatrician should also be made as there is an association with branchio-oto-renal and Pendred syndromes. Hearing aids should be recommended to all patients, and cochlear implants have been shown to be a safe and viable option.
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☆ The views and opinions expressed in this manuscript do not necessarily reflect those of the United States Air Force, the Department of Defense, or the United States Government.
PII: S1871-4048(06)00042-6
doi:10.1016/j.pedex.2006.03.004
Published by Elsevier Inc.
Volume 1, Issue 2 , Pages 142-144, June 2006
