Disclaimer: The information contained within the Grand Rounds Archive is intended for use by doctors and other health care professionals. These documents were prepared by resident physicians for presentation and discussion at a conference held at Baylor College of Medicine in Houston, Texas. No guarantees are made with respect to accuracy or timeliness of this material. This material should not be used as a basis for treatment decisions, and is not a substitute for professional consultation and/or peer-reviewed medical literature. Enlarged Vestibular Aqueduct Syndrome in the Pediatric Population Why is enlarged vestibular aqueduct important to all of us? It is actually the most commonly identified inner ear bony malformation in children with sensorineural hearing loss of unknown etiology. In today’s day and age, it has an increasing frequency and this newer generation of otolaryngologists being trained is going to see it more often than not. I consider this increasing frequency twofold. Number one, the imaging studies we use to evaluate the temporal bone are getting more detailed and providing more information as technology progresses. These cuts are getting finer and finer and we are being able to identify finer structures. Secondly, these children with profound sensorineural hearing loss are more often being referred to cochlear implantation teams. These teams are often getting these imaging studies and again helping us find more of these enlarged vestibular aqueduct syndromes. So, my goal today is just to inform us as a general population of otolaryngologists of some key points that we have to remember when seeing patients with this entity. Mondini, the Italian physician, in 1791, first identified these inner ear abnormalities using tomographs. He was the first to identify these inner ear abnormalities. In 1978, Valvasorri and Clemis reviewed over 3000 polytomographs and noted 50 patients with enlarged vestibular aqueducts. It was Valvasorri who actually first coined the term “enlarged vestibular aqueduct syndrome.” What is the incidence? In a population of children with sensorineural hearing loss, if you obtain a CT of the temporal bone, you can expect to see between 1-12% who have enlarged vestibular aqueducts. The female to male ratio is 3:2 and it is more often than not bilateral. The incidence in the general population remains unknown at this time. What is the pathophysiology behind this? Enlarged vestibular aqueduct syndrome affects both the auditory and vestibular systems. It is basically a congenital malformation of the temporal bone that predisposes the affected persons to early onset of hearing loss and vestibular disturbance. Pictured here is what a typical inner ear looks like the in the temporal bone. Here we see the vestibular aqueduct as well as the endolymphatic duct traversing to come to the endolymphatic sac, which sits in the posterior cranial fossa. The diagram on this side shows a short, stubby, large endolymphatic duct and an enlarged endolymphatic sac. To move on and briefly go over ear development; the ear starts developing around the sixth week of gestation. The first and second arch give rise to the sixth helix. By the eighth week, the surface epiderm of the first pharyngeal groove starts to grow inward towards the middle ear. This becomes the epithelial layer of the tympanic membrane. By the 12 th week, the helix develops and by the 20 th week you have obtained full adult shape. It is not so later in life when the auricle obtains its full adult size. Moving on to middle ear development, around the sixth week of gestation, the malleolus and incus appear as a single mass. About a week later, the stapes arch appears and by the eighth week we begin to see the joints of the malleal, incudal, and incudostapedial joints . At birth, the ossicles are adult size and shape and only slightly grow postnatally. The mastoid area begins to develop around one year of age. Inner ear development is interesting in that it begins very early. In the third week, the neuroectoderm and ectoderm form the otic vesicle and it is not until the sixth week when the semicircular canals begin to take shape, as seen here, and the cochlea begins to form its basal turn. By the ninth week, the semicircular canals and the utricle are fully formed, the cochlea begins to take its turns, and by the 12 th week, the cochlea has a full 2.5 turns. That was the labyrinthine portion of the inner ear. The vestibular aqueduct and the endolymphatic sac are unique in that the labyrinth obtains its adult shape and size by mid fetal life, but the vestibular aqueduct and the endolymphatic sac undergo changes late in fetal life and undergo changes in the postnatal life up to age three. As you remember, the endolymphatic sac sits in the posterior cranial fossa. The posterior cranial fossa continues to grow postnatally and it tends to draw the vestibular aqueduct and the endolymphatic duct, thus giving it the long, narrowed, and J-shaped appearance. Around the fourth week of gestation, the vestibular aqueduct appears and is at its largest dimension at the fifth week. The vestibular aqueduct around the fifth week of gestation is short, stubby, and wide. Jackler proposed that some insult might occur around the fifth week, causing it to be arrested in development. Going on to further anatomy of the labyrinth; here we see the endolymphatic sac, which comes across attached to the inner ear with the endolymphatic duct. If you notice, the endolymphatic duct is connected to the utricle and saccule as well as the cochlea via the ductus reunion. This comes to important play when we talk about some of the mechanisms of how hearing loss occurs in enlarged vestibular aqueduct syndrome. Before I progress further, the temporal bone anatomy can sometimes be challenging, especially for us young otolaryngologists or otolaryngologists that typically do not view these films. To give you a brief overview around the vestibular aqueduct, I would like to point out some common structures that we see in a normal CT scan. So again, here we have an axial view of the CT of the temporal bone. You see the superior semicircular canal and the common crus and the posterior semicircular canal along with the sigmoid sinus.If we take some cuts down, we can see the internal auditory canal and "Bill’s bar" at which point the labyrinthine segment of VII comes off and starts forming the first facial nerve. If you continue to take further cuts down, you can see the tympanic segment of VII and you start seeing cuts of the lateral semicircular canal and the little circle at the end is the posterior semicircular canal. This is a good landmark to help identify our point of interest and this is the vestibular aqueduct. Here is a typical vestibular aqueduct in size and shape. Taking on further cuts down, the vestibular aqueduct again opens up in the posterior cranial fossa and that is the endolymphatic sac area. That is typically where the endolymphatic sac sits. Again seen here, the cochlea with the modiolus and the oval window and the vestibule. If you take one more cut down below this on the temporal bone, you will start to see the stapes superstructure as well as the other ossicles. All these inner ear malformations tend to be associated with each other. To go over this, Valvasorri found that 62% of these enlarged vestibular aqueducts were associated with other inner ear abnormalities. Pictured here to your left is the hypoplastic cochlea as well as, on the right, a Mondini’s cochlea, which has 1.5 turns. Other abnormalities associated with enlarged vestibular aqueduct include widening of the vestibule and the lateral semicircular canal, and hypoplasia/dysplasia of the cochlea. There are two genetic syndromes in particular that we have to think about when we see these patients with enlarged vestibular aqueduct syndrome. The two genetic syndromes associated are Pendred’s syndrome and branchial otorenal syndrome. Pictured here is what a patient would look like who suffers from branchial otorenal syndrome. Basically it is an autosomal disorder that shows conductive or mixed hearing loss. They typically have cup-shaped and everted pinna, bilateral branchial cleft fistulas and cysts, and renal dysplasia. The precise incidence of this disorder is not known. Moving on, enlarged vestibular aqueduct syndrome is associated with Pendred’s syndrome. This is an autosomal recessive disorder, shows variable bilateral hearing loss with the typical U‑shaped audiogram. These patients are usually euthyroid, but present with goiters. Part of the workup is ordering a perchlorate test, which end up being positive. The gene has been mapped to the long arm of chromosome 7 in Pendred’s syndrome and has been named SCL26A4. The protein from this gene is actually been identified as well. It is the Pendred protein and it has been postulated to have effects with regards to electrolyte balance in both the thyroid and the kidney. It is interesting in that this electrolyte balance might give us clues in the future with regards to what is occurring in the inner ear because of the ion transport mechanisms known in the endolymphatic sac. Overall, Pendred’s syndrome constitutes 10% of hereditary deafness. What is an enlarged vestibular aqueduct and what is normal? Willebrand in the 1970s had the largest series of temporal bones in which he just took cadaveric temporal bones and measured the vestibular aqueduct histologically. He found that anywhere from 0.4mm -1mm is what he considered normal. Valvasorri and Emmett took these studies and later 1970 studies and used them in their measurements. Valvasorri took a 1.5 mm size at the mid point of the distal end pictured here below. Arcand and Jackler took a 2.0 mm as their upper limits of normal and Levenson took a 2.0 mm size at the opening of the aqueduct. So there is great interest in seeing if you could get a CT scan to see if the size or the shape of the vestibular aqueduct could give you some insight into whether the person is at higher risk for losing his hearing. Zalzal from George Washington University looked at 15 children, studied their CT temporal bones, and followed them. He did not notice any correlation between the size of the vestibular aqueduct and their progression in hearing loss. Antonelli from the University of Florida in 1998 published a study in which he did state that vestibular aqueduct morphology and thickness did correlate. A follow-up study by Madden in 2003, unfortunately, did not support this finding and showed no correlation between the size of the vestibular aqueduct and a pure tone average. Overall, reading the literature, you cannot really build prognosis based on what the CT scans look like. What are the genetics behind it? Griffith from the University of Michigan, in 1996, was the first to report a family suffering from enlarged vestibular aqueduct. Based on his studies, he concluded an autosomal recessive or X-linked inheritance pattern was variable expressivity. Tong, in 1997, from the University of Utah, studied 25 patients and found these 25 patients, after reviewing their families and obtaining CTs of the temporal bones of their families, noted five positive family histories. Again, he found supporting evidence to support Griffith’s statement of autosomal recessive inheritance pattern, as pictured here. This is the study from Griffith in which his proband had bilaterally enlarged vestibular aqueduct syndrome in the audiogram pictured below. When he went to go look at his brother, he found that his brother did have an enlarged right-sided vestibular aqueduct and right-sided sensorineural hearing loss. What are the audiometric findings in our patients with enlarged vestibular aqueduct? What can we usually expect to see? It is usually bilateral sensorineural hearing loss. It usually presents at birth and initially at high frequencies. Often they progress during early life, or progress may be in a sudden or stepwise fashion. The literature has shown that it is often associated with seemingly insignificant head trauma, and in some patients eventually leads to profound sensorineural hearing loss. These graphs pictured here are from the Maddox 2003 review article in which he found 39% of his patients to have a down-sloping look to the audiogram, 35% to have a flat, 17% to have a cookie-cutter appearance, and 10% to have an upsloping. What he ended up doing was following these exact same patients for another three years to see how their audiograms changed. He noted 50% to have stable hearing over those three years. Twenty-eight percent had fluctuating or fluctuating with progressive picture and 10% had a progressive type of audiogram. Oftentimes, we can see conductive hearing loss observed, especially in the lower frequencies in our patients, despite having clinically normal middle ear and tympanograms. There have been several theories as to why this conductive component occurs. Such theories include decrease of stapes mobility from increased endolymphatic sac pressure, stapes ossification, or other ossicular dysfunction. The literature has not been able to support any one of these theories. Coming back to hearing loss after minor trauma, there have been many theories as to what leads to this. Some proponents say there may be a toxic buildup of metabolites or disruption of normal endolymphatic homeostasis. Others argue there may be a perilymph fistula or transmission or hydraulic forces into the cochlea from the endolymphatic sac with these head trauma. Madden, in his review article, again in 2003, reviewed his 77 patients. The reason I mention his article so frequently, it is one of the largest studies in enlarged vestibular aqueduct, with 77 patients. Of these 77 patients that he followed, only three of them had experienced sudden deterioration after head trauma. Madden then stated that it might not be as significant as once thought. So, what is the cause of this hearing loss after minor trauma? Well, the one theory that has really stood the test of time thus far is in Levenson’s 1989 reflex theory. In this, as you remember, the endolymphatic sac sits in the posterior cranial fossa and with head trauma you can get increased pressure or fluctuations of CSF, and this might compress the endolymphatic sac and compress its hyperosmotic endolymphatic sac contents through the enlarged vestibular aqueduct to the endolymphatic duct and push it into the cochlea. The hyperosmotic contents may cause neuroepithelial damage and thus lead to the sensorineural hearing loss. This will become an interesting point when we look at the surgical interventions for enlarged vestibular aqueduct syndrome. Other patients who have been noted to have vestibular dysfunction—typically seen in a minority of patients and more often in adults. Of our patients, typically 4-29% would have vestibular symptoms. Most of the literature published with these vestibular dysfunctions are based on small studies of two to five patients, so larger studies are needed. Again, the etiology is postulated to be related to the transmission of intracranial pressure fluctuations stimulating the vestibular sensory receptors. Again, that has not been fully investigated. The new hot topic in this day and age is magnetic resonance imaging. The detail in MRI is getting amazingly good. Pictured here below to your left is a three-dimensional reconstruction of the inner ear. Using MRI gives us a better appreciation of the soft tissue changes seen, as here, with the enlarged endolymphatic duct or enlarged endolymphatic sac. Again, looking further with these MRIs gives us good pictures of the cochlea as well as the vestibule and the semicircular canal. In the future, MRI is going to be complimentary to CT of the temporal bone, and actually Dahlan, in 1997 published an article supporting this complimentary use. What is the management of patients with enlarged vestibular aqueduct syndrome, which is all we want to know when we treat our patients. Well, if you notice, my theme throughout the course of this talk has been that we do not know much about the mechanism of hearing loss and the mechanism of vestibular disturbance. Without knowing the pathophysiology, management has been somewhat difficult and challenging. Overall, we recommend early aggressive use of hearing aids to amplify hearing in these children because even mild forms of hearing loss can have great social and cognitive sequelae. We also recommend early speech and language therapy. What are the surgical interventions? Overall, the theories have been if there is a surgery that we can provide these children that would stop progression of the sensorineural hearing loss, that would be great. Jackler was one of the first to start doing these studies, and in the 90s he had seven patients in which he performed endolymphatic shunts from the sac to the mastoid. One hundred percent of these seven patients had worse progression of their hearing, and actually 57% had severe hearing loss. So, since Jackler’s study, this fell out of favor. It was not until Wilson, from Oregon Health Science Center, in 1997, published an article in which he operated on six patients. His procedure was stuffing the endolymphatic sac with fascia, and he noted that six of seven of his patients maintained stable hearing. He performed a simple mastoidectomy and unroofed the endolymphatic sac, pictured here. He noted enlarged endolymphatic sacs. He would make a small incision of the endolymphatic sac and gently push temporalis fascia strips into the sac. It was Welling from Ohio State, in 1998, who took up the reins with surgery on the endolymphatic sac to stop this progression of hearing loss. Describing his surgical operation, after doing a simple mastoidectomy of facial nerve and the posterior semicircular canal, he unroofs the endolymphatic sac and actually gets a temporal muscle fascia plug to stuff underneath the posterior semicircular canal and occlude the endolymphatic duct. After this, he gets his bone chips and uses them to compress it further and hold this muscle plug in place. Recalling the Levinson theory of reflux, in which these hyperosmotic contents of the sac get refluxed into the cochlea causing sensorineural hearing loss, may make one wonder if, in compressing the sac, you might get that same reflux and cause sensorineural hearing loss. In his first study of ten patients in 1998, he noticed no change in the rate of hearing and no severe outcomes. He followed up his study, in 1999, with another ten patients; but in this follow-up study he had 90% of his patients with worse hearing and 50% had severe sensorineural hearing loss. So, in the review article, this is the largest series of endolymphatic sac occlusions to date, and if you notice the percentage of worse is quite high and the percent of severe hearing loss, 20% - 50% is unacceptable. Based on these studies, surgical intervention to prevent the progression of hearing loss with enlarged vestibular aqueduct was described and abandoned many years ago. What can we do for these patients surgically? Cochlear implants have been the key to the future of these patients. Although it has been proposed that these children may be suitable for implantation since 1992, it was not until 1995 when a few successfully implanted children were reported. As a last result, these cochlear implants provide one successful treatment option for the management of these patients. Many of you will be thinking, “Okay, well if cochlear implants are the solution, why aren’t more people doing it?” Well, the whole theory of enlarged vestibular aqueduct is that there is a large communication between the endolymphatic duct and the inner ear. People say when you drill your cochleostomy that you might get increasing gushers and cause sensorineural hearing loss. Looking over the literature review, you notice, yes there have been noted gushes when you do the cochleostomies, but they have all been well managed with muscle sealing and muscle plugging and the only sequelae were vomiting and dizziness for one or two days. With the newer studies, there have been no gushers noted and no postoperative sequelae. Fahy had the most recent article, in 2001, in which he implanted four patients and had excellent outcomes in each of these four patients. Thus, after reviewing the literature, enlarged vestibular aqueduct syndrome is not a contraindication to cochlear implantation and, in fact, these patients are ideal because they have well developed speech and language prior to their deafness, so once they get the cochlear implants, they do quite well. What do we do for counseling our young patients? Avoid contact activities and contact sports such as those in which head trauma is inevitable. More importantly for our little children, tell them to wear seatbelts as well as helmets when they play. What is the future of enlarged vestibular aqueduct syndrome? One, we need larger studies extending into adulthood to see what the epidemiology and what the hearing losses are. Two, I think the future is with the genetic tests. These genetic tests will help define the need for further work-up as well as need for insight into the pathophysiology of what is going on. In particular, isolation of the gene and gene products may allow future target therapy to help stop the hearing loss progression. In my opinion, it is these genetic tests and genetic studies that are going to save these patients’ hearing from progressing, not the middle ear surgeries. So, that was a lot of information in a short amount of time. What do I want you as an audience to take away? If you take away four things from this talk, these are the four. One, enlarged vestibular aqueduct is the most commonly identified inner ear bony malformation in children with sensorineural hearing loss of unknown cause. Two, the mechanisms of hearing loss and vertigo in enlarged vestibular aqueduct syndrome are not known. Three, literature review supports the feasibility of cochlear implantation in these children, but literature does not support surgical intervention of the inner ear to prevent further hearing loss. Lastly, recommend the early use of hearing aids and caution patients in regards to head trauma and the use of safety mechanisms such as seatbelts and helmets. Case Presentation: JA is a 7-year-old Latin-American female, otherwise healthy, who presented to her primary care physician with complaints of hearing loss. Patient had failed multiple hearing screens at school and was first suspected to have hearing loss at 6 years-old. Patient was referred to the Audiology Department and Otolaryngology Department at Texas Children’s Hospital for further assessment. Patient denies history of infection, otalgia, odynophagia, dysphagia, tinnitus, or fluctuating hearing loss. She has no significant past medical or surgical history and does not take medication. The pregnancy and delivery were uneventful. Language and speech development were not delayed. Family medical history is negative for consanguinity or early childhood deafness. Physical exam revealed no abnormalities. Craniofacial structures were normally developed. The tympanic membranes were intact and mobile with no evidence of ossicular dysfunction. The cranial nerves were intact bilaterally, and cerebellar testing and Rhomberg’s were normal. Routine blood chemistries, urinalysis, and thyroid function tests were normal. FTA ABS, HSV IgM, Rubella IgM, TORCH, and Connexin 26 were negative. Audiogram revealed a right mild sensorineural loss at 250 hz, sloping to a moderate sensorinuerual loss at 500 Hz-1000Hz and further sloping to a moderately severe to severe SNHL at 1500-8000Hz. Acoustic immittance measures are consistent with normal middle ear function. The left ear revealed hearing within normal limit, acoustic immittance measures are consistent with normal middle ear function. A CT scan of the temporal bone revealed an enlarged right side vestibular aqueduct which measured approximately 1.8mm. The vestibule, semicircular canals and cochlea appeared normal. The left inner ear was without abnormalities. Bibliography: Antonelli PJ, Nall AV, Lemmerling MM, Mancuso AA, Kubilis, PS. Hearing loss with cochlear modiolar defects and large vestibular aqueducts. Am J Otol 1998;19:306-312. Antonelli, PJ, Varela AE, Mancuso AA. Diagnostic yield of high-resolution CT for pediatric sensorineural hearing loss. Laryngoscope 1999;109:1642-1647. 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Vestibular disturbance in patients with large vestibular aqueduct syndrome. Acta Otolaryngol 1999;119:641-646. Zalzal GH, Tomaski SM, Vezina LG, Bjornsti P, Grundfast KM. Enlarged Vestibular Aqueduct and sensorineural hearing loss in childhood. Arch Otolaryngol Head Neck Surg 1995;121:23-28. Grand Rounds Archive | Department Home page BCM Public | BCM Intranet | Privacy Notices | Contact BCM | BCM Site Map | ©2001-2006 Baylor College of Medicine
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