Enlarged vestibular aqueduct

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Enlarged vestibular aqueduct
Other namesEnlarged vestibular aqueduct, Dilated vestibular aqueduct or Widened vestibular aqueduct
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Interior of right osseous labyrinth

Large vestibular aqueduct is a structural deformity of the inner ear. Enlargement of this duct is one of the most common inner ear deformities and is commonly associated with hearing loss during childhood. [1] The term was first discovered in 1791 by Mondini when he was completing a temporal bone dissection. It was then defined by Valvassori and Clemis as a vestibular aqueduct that is greater than or equal to 2.0 mm at the operculum and/or greater than or equal to 1.0 mm at the midpoint. [2] Some use the term enlarged vestibular aqueduct syndrome, but this is felt by others to be erroneous as it is a clinical finding which can occur in several syndromes.[ citation needed ]

Contents

Symptoms

Although large vestibular aqueducts are a congenital condition, hearing loss may not be present from birth. Age of diagnosis ranges from infancy to adulthood, and symptoms include fluctuating and sometimes progressive sensorineural hearing loss and disequilibrium. It is possible that a small portion of those with large vestibular aqueducts will not exhibit auditory symptoms such as hearing loss. While this is uncommon, hearing loss can progress later in life, especially after head trauma. [3] Hearing loss can be unilateral or bilateral and can be sensorineural, conductive, or mixed. Vestibular symptoms, such as vertigo and imbalance, occur in adult patients 45% of the time. [4]

Pathology

The cochlea and vestibule, viewed from above. (Vestibular aqueduct labeled at bottom right.) Gray923.png
The cochlea and vestibule, viewed from above. (Vestibular aqueduct labeled at bottom right.)

The vestibular aqueduct acts as a canal between the inner ear and the cranial cavity. Running through it is a tube called the endolymphatic duct, which normally carries a fluid called endolymph from the inner ear to the endolymphatic sac in the cranial cavity. When the endolymphatic duct and sac are larger than normal, as is the case in large vestibular aqueduct syndrome, endolymph is allowed to travel back from the endolymphatic sac into the inner ear. This often results in fluctuations in hearing levels. Enlarged vestibular aqueducts are caused by mutations in gene SLC26A4, which is also associated with Pendred syndrome and non-syndromic recessive deafness. Enlarged vestibular aqueducts often occur with other inner ear development problems, such as cochlear deformities. Enlarged vestibular aqueducts are part of the classic Mondini deformity. Enlarged vestibular aqueducts with enlarged endolymphatic sacs occur in Pendred syndrome, which is caused by a defect on chromosome 7q31. [1] Enlarged vestibular aqueducts can also occur in branchio-oto-renal syndrome, CHARGE syndrome and renal tubular acidosis.

Enlarged vestibular aqueducts can be bilateral or unilateral.

Hearing loss caused by large vestibular aqueduct syndrome is not inevitable, although people with the syndrome are at a much higher risk of developing hearing loss than the general population. Hearing loss is very likely.

Diagnosis

Enlarged vestibular aqueducts are commonly picked up after newborn hearing screen when a child is identified as having a hearing loss. The hearing loss is commonly mixed and can be of any degree when first identified. The conductive component is due to a third window effect caused by the widened vestibular aqueduct. During an audiologic assessment, an air-bone gap in the low frequencies can occur due to the enlarged vestibular aqueduct acting as a third mobile window. Hearing loss in the contralateral ear to the enlarged vestibular aqueduct can also occur due to the chemical composition on both sides. [5] Torticollis has also been found to be an indicator of an enlarged vestibular aqueduct in children. [6] Identification of the enlarged vestibular aqueduct in a child is usually by MRI scan which identifies the fluid within the endolymphatic duct and sac. CT scan may be needed to see the vestibular aqueduct clearly. In adults, CT scan may be the first investigation. In order to diagnose the cause of the enlarged vestibular aqueduct, the physician will need a detailed family history, full examination to include vestibular examination and, if a bilateral finding, molecular genetic testing as appropriate. With unilateral enlarged vestibular aqueducts, molecular genetic testing is currently not recommended.

Management

There is no treatment to correct an enlarged vestibular aqueduct. Any hearing loss will need management with amplification and support in education and at work. If the hearing loss becomes severe to profound, cochlear implants can be of significant value. Vestibular disturbance is usually short-lived and associated with head trauma, but significant vestibular hypofunction may require rehabilitation.

People with enlarged vestibular aqueducts are advised to avoid head trauma where possible. This usually means avoiding contact sports such as football, boxing, rugby, horse riding, trampolining and other sports where head injury may occur. Some have symptoms when flying and should limit these activities if affected.

Related Research Articles

<span class="mw-page-title-main">Inner ear</span> Innermost part of the vertebrate ear

The inner ear is the innermost part of the vertebrate ear. In vertebrates, the inner ear is mainly responsible for sound detection and balance. In mammals, it consists of the bony labyrinth, a hollow cavity in the temporal bone of the skull with a system of passages comprising two main functional parts:

<span class="mw-page-title-main">Ménière's disease</span> Disorder of the inner ear

Ménière's disease (MD) is a disease of the inner ear that is characterized by potentially severe and incapacitating episodes of vertigo, tinnitus, hearing loss, and a feeling of fullness in the ear. Typically, only one ear is affected initially, but over time, both ears may become involved. Episodes generally last from 20 minutes to a few hours. The time between episodes varies. The hearing loss and ringing in the ears can become constant over time.

<span class="mw-page-title-main">Cochlea</span> Snail-shaped part of inner ear involved in hearing

The cochlea is the part of the inner ear involved in hearing. It is a spiral-shaped cavity in the bony labyrinth, in humans making 2.75 turns around its axis, the modiolus. A core component of the cochlea is the organ of Corti, the sensory organ of hearing, which is distributed along the partition separating the fluid chambers in the coiled tapered tube of the cochlea.

<span class="mw-page-title-main">Semicircular canals</span> Organ located in innermost part of ear

The semicircular canals or semicircular ducts are three semicircular, interconnected tubes located in the innermost part of each ear, the inner ear. The three canals are the horizontal, superior and posterior semicircular canals.

<span class="mw-page-title-main">Saccule</span> Bed of sensory cells in the inner ear

The saccule is a bed of sensory cells in the inner ear. It translates head movements into neural impulses for the brain to interpret. The saccule detects linear accelerations and head tilts in the vertical plane. When the head moves vertically, the sensory cells of the saccule are disturbed and the neurons connected to them begin transmitting impulses to the brain. These impulses travel along the vestibular portion of the eighth cranial nerve to the vestibular nuclei in the brainstem.

<span class="mw-page-title-main">Ear</span> Organ of hearing and balance

An ear is the organ that enables hearing and body balance using the vestibular system. In mammals the ear is usually described as having three parts: the outer ear, the middle ear and the inner ear. The outer ear consists of the pinna and the ear canal. Since the outer ear is the only visible portion of the ear in most animals, the word "ear" often refers to the external part alone. The middle ear includes the tympanic cavity and the three ossicles. The inner ear sits in the bony labyrinth, and contains structures which are key to several senses: the semicircular canals, which enable balance and eye tracking when moving; the utricle and saccule, which enable balance when stationary; and the cochlea, which enables hearing. The ear is a self cleaning organ through its relationship with earwax and the ear canals. The ears of vertebrates are placed somewhat symmetrically on either side of the head, an arrangement that aids sound localization.

<span class="mw-page-title-main">Endolymph</span> Inner ear fluid

Endolymph is the fluid contained in the membranous labyrinth of the inner ear. The major cation in endolymph is potassium, with the values of sodium and potassium concentration in the endolymph being 0.91 mM and 154 mM, respectively. It is also called Scarpa's fluid, after Antonio Scarpa.

<span class="mw-page-title-main">Sensorineural hearing loss</span> Hearing loss caused by an inner ear or vestibulocochlear nerve defect

Sensorineural hearing loss (SNHL) is a type of hearing loss in which the root cause lies in the inner ear or sensory organ or the vestibulocochlear nerve. SNHL accounts for about 90% of reported hearing loss. SNHL is usually permanent and can be mild, moderate, severe, profound, or total. Various other descriptors can be used depending on the shape of the audiogram, such as high frequency, low frequency, U-shaped, notched, peaked, or flat.

<span class="mw-page-title-main">Pendred syndrome</span> Medical condition

Pendred syndrome is a genetic disorder leading to congenital bilateral sensorineural hearing loss and goitre with euthyroid or mild hypothyroidism. There is no specific treatment, other than supportive measures for the hearing loss and thyroid hormone supplementation in case of hypothyroidism. It is named after Vaughan Pendred (1869–1946), the British doctor who first described the condition in an Irish family living in Durham in 1896. It accounts for 7.5% to 15% of all cases of congenital deafness.

Mondini dysplasia, also known as Mondini malformation and Mondini defect, is an abnormality of the inner ear that is associated with sensorineural hearing loss.

<span class="mw-page-title-main">Vertigo</span> Type of dizziness where a person has the sensation of moving or surrounding objects moving

Vertigo is a condition in which a person has the sensation of movement or of surrounding objects moving when they are not. Often it feels like a spinning or swaying movement. This may be associated with nausea, vomiting, sweating, or difficulties walking. It is typically worse when the head is moved. Vertigo is the most common type of dizziness.

<span class="mw-page-title-main">Perilymph</span> Extracellular fluid located within the inner ear

Perilymph is an extracellular fluid located within the inner ear. It is found within the scala tympani and scala vestibuli of the cochlea. The ionic composition of perilymph is comparable to that of plasma and cerebrospinal fluid. The major cation in perilymph is sodium, with the values of sodium and potassium concentration in the perilymph being 138 mM and 6.9 mM, respectively. It is also named Cotunnius' liquid and liquor cotunnii for Domenico Cotugno.

<span class="mw-page-title-main">Vestibular aqueduct</span> Orifice

At the hinder part of the medial wall of the vestibule is the orifice of the vestibular aqueduct, which extends to the posterior surface of the petrous portion of the temporal bone.

Hearing loss with craniofacial syndromes is a common occurrence. Many of these multianomaly disorders involve structural malformations of the outer or middle ear, making a significant hearing loss highly likely.

Pendrin is an anion exchange protein that in humans is encoded by the SLC26A4 gene . Pendrin was initially identified as a sodium-independent chloride-iodide exchanger with subsequent studies showing that it also accepts formate and bicarbonate as substrates. Pendrin is similar to the Band 3 transport protein found in red blood cells. Pendrin is the protein which is mutated in Pendred syndrome, which is an autosomal recessive disorder characterized by sensorineural hearing loss, goiter and a partial organification problem detectable by a positive perchlorate test.

Endolymphatic hydrops is a disorder of the inner ear. It consists of an excessive build-up of the endolymph fluid, which fills the hearing and balance structures of the inner ear. Endolymph fluid, which is partly regulated by the endolymph sac, flows through the inner ear and is critical to the function of all sensory cells in the inner ear. In addition to water, endolymph fluid contains salts such as sodium, potassium, chloride and other electrolytes. If the inner ear is damaged by disease or injury, the volume and composition of the endolymph fluid can change, causing the symptoms of endolymphatic hydrops.

<span class="mw-page-title-main">Autoimmune inner ear disease</span> Medical condition

Autoimmune inner ear disease (AIED) was first defined by Dr. Brian McCabe in a landmark paper describing an autoimmune loss of hearing. The disease results in progressive sensorineural hearing loss (SNHL) that acts bilaterally and asymmetrically, and sometimes affects an individual's vestibular system. AIED is used to describe any disorder in which the inner ear is damaged as a result of an autoimmune response. Some examples of autoimmune disorders that have presented with AIED are Cogan's syndrome, relapsing polychondritis, systemic lupus erythematosus, granulomatosis with polyangiitis, polyarteritis nodosa, Sjogren's syndrome, and Lyme disease.

<span class="mw-page-title-main">Endolymphatic sac tumor</span>

An endolymphatic sac tumor (ELST) is a very uncommon papillary epithelial neoplasm arising within the endolymphatic sac or endolymphatic duct. This tumor shows a very high association with Von Hippel–Lindau syndrome (VHL).

Dark cells are specialized nonsensory epithelial cells found on either side of the vestibular organs and lining the endolymphatic space. These dark-cell areas in the vestibular organ are structures involved in the production of endolymph, an inner ear fluid, secreting potassium towards the endolymphatic fluid. Dark cells take part in fluid homeostasis to preserve the unique high-potassium and low-sodium content of the endolymph and also maintain the calcium homeostasis of the inner ear.

Cochlear hydrops is a condition of the inner ear involving a pathological increase of fluid affecting the cochlea. This results in swelling that can lead to hearing loss or changes in hearing perception. It is a form of endolymphatic hydrops and related to Ménière's disease. Cochlear hydrops refers to a case of inner-ear hydrops that only involves auditory symptoms and does not cause vestibular issues.

References

  1. 1 2 S. Usami; Satoko Abe; Mike D. Weston; Hideichi Shinkawa; Guy Van Camp; William J. Kimberling (1999), "Non-syndromic hearing loss associated with enlarged vestibular aqueduct is caused by PDS mutations", Human Genetics, 104 (2): 188–192, doi:10.1007/s004390050933, PMID   10190331, S2CID   3116063
  2. ↑ Yang, Christina (2016). "Vestibular Pathology in Children with enlarged vestibular aqueduct". The Laryngoscope. 126 (10): 2344–50. doi:10.1002/lary.25890. PMID   26864825.
  3. ↑ Madden, Colm; Halsted, Mark; Benton, Corning; Greinwald, John; Choo, Daniel (July 2003), "Enlarged Vestibular Aqueduct Syndrome in the Pediatric Population", Otology & Neurotology, 24 (4): 625–632, doi:10.1097/00129492-200307000-00016, PMID   12851556, S2CID   44980735
  4. ↑ Grimmer, J (2007). "Vestibular symptoms in children with enlarged vestibular aqueduct anomaly". International Journal of Pediatric Otorhinolaryngology. 71 (2): 275–82. doi:10.1016/j.ijporl.2006.10.010. PMID   17113162.
  5. ↑ Greinwald, J (2013). "Significance of unilateral enlarged vestibular aqueduct". The Laryngoscope. 123 (6): 1537–46. doi:10.1002/lary.23889. PMID   23401162.
  6. ↑ Brodsky, J (2020). "Torticollis in children with enlarged vestibular aqueducts". International Journal of Pediatric Otorhinolaryngology. 131: 109862. doi:10.1016/j.ijporl.2020.109862. PMID   31927148.


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