Embryologic Origins of Hearing Loss What’s the relationship between prenatal development and congenital and progressive hearing impairment? Otolaryngologist Kelley M. Dodson led an online chat exploring this question. The Leader listened in. Overheard
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Overheard  |   January 01, 2015
Embryologic Origins of Hearing Loss
Author Notes
  • Kelley M. Dodson, MD, is associate professor of otolaryngology/head and neck surgery and residency program director at Virginia Commonwealth University Medical Center in Richmond. Her clinical and research interests include pediatric otolaryngology, congenital and hereditary hearing loss, unilateral hearing loss, vestibular disorders, tinnitus and pediatric sinusitis, and she has published extensively on pediatric and genetic hearing loss, risk factors associated with unilateral and bilateral hearing loss, and nonsyndromic mitochondrial deafness. dodson@mcvh-vcu.edu
    Kelley M. Dodson, MD, is associate professor of otolaryngology/head and neck surgery and residency program director at Virginia Commonwealth University Medical Center in Richmond. Her clinical and research interests include pediatric otolaryngology, congenital and hereditary hearing loss, unilateral hearing loss, vestibular disorders, tinnitus and pediatric sinusitis, and she has published extensively on pediatric and genetic hearing loss, risk factors associated with unilateral and bilateral hearing loss, and nonsyndromic mitochondrial deafness. dodson@mcvh-vcu.edu×
Article Information
Development / Hearing Disorders / Overheard
Overheard   |   January 01, 2015
Embryologic Origins of Hearing Loss
The ASHA Leader, January 2015, Vol. 20, online only. doi:10.1044/leader.OV.20012015.np
The ASHA Leader, January 2015, Vol. 20, online only. doi:10.1044/leader.OV.20012015.np
Carol Runyan: As complicated as the ear structure and function are, do you have any hypotheses about why it is? that development begins and completes as early as it does in the fetus? I have seen many children born where the mother was unaware of her pregnancy and, as a result, had no prenatal care and abuse of alcohol, drugs, etc. Very often these children have ear deformities and hearing loss as well as other issues.
Kelley Dodson: I think that is due to its nature as a part of the neurosensory system. The ear has to develop in parallel with the developing brain. Sadly, most of this development takes place before women are aware they may be pregnant and so it is highly susceptible to teratogens and environmental influences.
Bridget Gonzalez: Is there more risk of spinal meningitis, the younger the infant is, due to developmental ossification of the temporal bone?
Dodson: Definitely the risk of meningitis is higher from otitis media in infants and children who have developmental anomalies of the inner ear that lead to direct communication between the ear and brain, commonly from a patent cochlear aqueduct or the like. At birth, theoretically there should be complete ossification of the middle ear cavity (albeit quite thin) that helps separate the ear and brain. However, infants younger than 3 months are at greater risk, in general, for sepsis or generalized spread from infections due to the immaturity of the immune system, and bacteria can travel via preformed pathways (along veins, etc.) to cause meningitis.
George Cook: What effect does methadone, and/or other substance abuse, have on the fetus and hearing of newborn?
Dodson: We consider methadone to be potentially ototoxic. There are reports of sudden hearing loss that can occur with methadone intoxication and, in general, substance abuse during pregnancy can cause widespread developmental anomalies—like fetal alcohol syndrome and/or neurologic issues—that can also affect the ear. These babies typically have several other risk factors known to be associated with hearing loss as well (low birth weights, prematurity and NICU stays), so we would certainly pay close attention to newborn hearing screening and provide appropriate follow-up during infancy.
Vaibhavi Dharkar: What is the relationship between hearing loss and skin disease, is this in any way related to the fact that both the skin and sensory cells are a product of the ectoderm?
Kelley Dodson: Exactly! The skin cells and the neurosensory cells are both from ectodermal origin.
Gonzalez: Hi, Just to clarify, are you saying that you can occasionally see a congenital cholesteatoma with Treacher-Collins, Goldenhars or Omenn’s syndrome?
Dodson: We see congenital cholesteatoma more frequently if there is aural atresia (meaning the canal is underdeveloped), because the epithelium that lines the ear canal may be trapped inside and not be able to get out. I don’t think that congenital cholesteatoma of the middle ear has an increased associated with these syndromes, but definitely of the ear canal.
Margo McNiven: Is a pre-auricular or post-auricular tag or cyst considered a marker for hearing loss? Or is hearing loss only a concern when the tag or cyst is seen in conjunction with BOR [branchiootorenal syndrome]?
Dodson: There is a small association of an isolated pit or tag with hearing loss apart from BOR. Whenever I see a child with a pit or tag that appears nonsyndromic, I take a detailed history and physical and get an audiogram just to be sure.
Christine Cook: What is the best practice for follow-up with children who have been diagnosed with meningitis?
Dodson: Definitely, part of the risk of hearing loss depends on the type of meningitis—it’s probably greatest with streptococcus pneumoniae, which causes a lot of inflammatory damage. I always like to get a hearing test as soon as the child is stable, and preferably before discharge home from the meningitis admit. If it cannot be done in the inpatient setting, they should see someone within a week or two after discharge. If there is bilateral severe-to-profound hearing loss, you want to be able to proceed with cochlear implantation sooner rather than later—before the inflammatory changes cause ossification within the cochlea.
Cook: If the child’s hearing is normal, what would you recommend for continued testing—every three months through the first year?
Dodson: I would say at a minimum, six-month intervals, but for children whose progression I am particularly concerned about (because many of these babies also receive antibiotics that may be ototoxic), I might see them back at three-month intervals for a year. There are no hard-and-fast guidelines, but following the guidelines set forth by the Joint Committee on Infant Hearing for babies with risk factors, until the age of 3 is a good general rule to follow for the postnatal infections and ototoxicitiy.
Liz Ehrstein: How often do you use embryology in clinical practice?
Dodson: Familiarity with embryology is really helpful in everyday clinical practice, particularly if you work with the pediatric population. If you work with syndromic or medically complicated patients, your knowledge of embryology when you evaluate their ear, head and neck can make you suspicious for other associated conditions that might not be readily apparent. For instance, if you are evaluating an infant who failed the newborn hearing test, you might be the first to note small branchial cysts in the neck and preauricular pits, and that would alert you to evaluate their kidneys for BOR syndrome, which is potentially life-saving.
Mary Violanti: Regarding preauricular pits, can a physician tell by examination if it’s a blind pit or one with potential for infection? Is it something that can be determined by imaging studies or is best approach observation?
Dodson: It is usually difficult to tell early on how deep and in which direction the pit is going. Sometimes it is obvious that the pit is really just a blind-ended depression, but if there is clearly a tract, the best option is observation. I generally recommend daily cleaning with a Q-tip as part of the child’s normal bathing/daily hygiene. If the tract becomes infected, then we would offer surgical intervention to excise. Usually we don’t need to image unless we have other concerns.
Alicia White: I had a patient that had bilateral anotia and also had bilateral absent cochlear nerves. From an embryologic development point of view, could there be any relationship between the two abnormalities?
Dodson: We see the association of outer and inner anomalies about 10 percent of the time. Probably the etiology involves a global insult to the nervous system and to the branchial arches at the early stages of development (Hillocks of His completely absent for the anotia) and the neurosensory otic placode not making any connection with the developing brain.
Runyan: What are your thoughts on surgical intervention for atresia in a child? I have heard many conflicting reports about the best time to begin the surgical process of canal reconstruction if it is the parental choice.
Dodson: Atresia surgery is definitely a controversial subject. A large part of the discussion involves whether it is bilateral or unilateral and if the patient is a “good” candidate. It also involves the parents’ expectations and goals for the child. If there is associated microtia, that should be addressed first, if that is desired by the patient/family. The problem with atresiaplasty is that over time, the canal tends to stenose down and never exfoliates normally—so it generally requires lifelong cleaning and has perhaps not the greatest hearing result long-term. If excellent hearing is really the goal, osseointegrated implants probably work better, but the decision depends on many factors.
Runyan: I am thinking of a child with bilateral atresia; she’s adopted, so there’s no family history available. She had had bilateral [bone-anchored hearing aids] with a band, and they were simply waiting till she was “big” enough for the surgery. I realize it is a multiple surgery process and I understand somewhat painful. Just curious.
Dodson: Usually in kids we want to wait until their bone thickness exceeds 4 mm so we can implant a 4-mm osseointegrated implant. It is approved in kids 5 and up, but if the child has good bone thickness you could do earlier, although insurance would probably not cover it. I would say overall it is not a very painful procedure. In younger children, we do the surgery in two stages, as their bone tends to be softer than teens/adults. We place the implant and keep it covered (nothing protruding through the skin) for three to six months to allow the titanium to bond with the bone. In the second stage, we place the “abutment,” which basically screws into the implant in the bone and protrudes out of the bone to allow the processor to clip on. When they clip on the processor, they get direct bone conduction on that side and excellent hearing results for conductive losses or single-sided profound deafness.
Leslie Heuser: Can you have just a first branchial cleft cyst that is not associated with hearing loss or syndromes?
Dodson: Yes, definitely. Most of the time the first branchial cleft cysts are isolated and not part of a syndrome. There are two types of first branchial cysts. The first is a more straightforward “duplication” of the ear canal, the second is a more winding tract through the parotid salivary gland and into the neck. Most are isolated abnormalities of fusion.
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January 2015
Volume 20, Issue 1