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The importance of hearing evaluation and treatment in Microtia

Microtia is accompanied by congenital absence or stenosis of the external auditory canal with variable middle ear anomalies this causes a significant conductive hearing loss (1-2).

Since microtia patients usually have a normal cochlea, they are not deaf, but have normal bone conduction hearing. Normal air conduction gives a hearing threshold of 15 to 20 dB. Microtia patients with aural atresia or stenosis hear with a maximum conductive loss with thresholds in the 60 to 70 dB range. As a reference, occlusion of a normal external auditory canal (EAC) with a finger reduces the hearing threshold to about 30dB. Since normal speech is in the 40 to 45 dB range, patients with unilateral microtia have significant unilateral hearing loss because their hearing threshold is higher.

With normal hearing in the contralateral ear, children with unilateral microtia and hearing loss are usually able to develop relatively normal speech. This is not true in patients with bilateral microtia or patients with unilateral microtia and unsuspected hearing loss in the non-microtic opposite ear (3-4).

Children with unilateral microtia seem to develop normally. Parents usually do not notice a significant difference between their young children and their siblings without microtia. This is the reason that unilateral hearing loss has been undertreated by many otolaryngologists and usually ignored by plastic surgeons treating microtia (5).

However, when children with microtia are older, and communication becomes more sophisticated, hearing issues become more obvious. Sound localization and hearing comprehension especially in noisy environments become more difficult (6-7).

Patients with microtia tend to turn their unaffected ear in the direction of sound, because the head itself casts a sound shadow which reduces comprehension in the unturned normal ear.

Once a child is 2.5 years of age, a computer tomography (CT) scan of the temporal bones can allow an otologist to determine if an atresia patient is a possible candidate for a canalplasty. The otologist needs to view the actual scan rather than the radiologist’s report. The Jahrsdorfer 10 point grading scale is commonly used to predict surgical candidacy depending on key features seen on the CT scan (8).

The treatment of hearing loss by an otologist should be coordinated with the surgeon responsible for the outer ear surgery. Traditionally, atresia repair is done after the costal cartilage ear reconstruction, since almost all otologists perform the ear canal reconstructions through a posterior mastoid skin incision to access the temporal bone. That approach compromises the blood supply of the mastoid skin that is used to cover the cartilage framework. However, prior atresia repair does not jeopardize the success of ear reconstruction using an implant covered by a vascularized fascia flap. With a Medpor ear reconstruction, atresia repair is best done before or at the same time as the ear reconstruction as the canal helps with positioning of the reconstructed pinna. Also, early atresia repair potentially improves hearing at a critical period of early brain development (9).

If the patient is not a candidate for atresia repair and a functional canal, a faux-canal can be created at the time of microtia reconstruction.

The faux-canal is reconstructed by resecting the entire microtic cartilage remnant with additional soft tissue down to the mastoid periosteum to increase the depth of the auricular concavity. The tragus is later made by medially transposing an anteriorly based mastoid flap, which contains a cartilage graft for support.

Dr. Tahiri is at the forefront of ear reconstruction. He will place your child best interest first. Feel free to contact him if you have any questions.

 

 

References

  1. Klockars T., Rautio J. (2009) Embryology and epidemiology of microtia. Facial Plastic Surgery. 25(3):145-148.
  2. Reed, R., Hubbard, M., & Kesser, B. W. (2016). Is There a Right Ear Advantage in Congenital Aural Atresia? Otology & Neurotology. 2016 Dec; 37 (10):1577-1582.
  3. Kesser, B. W., Krook, K., & Gray, L. C. (2013). Impact of unilateral conductive hearing loss due to aural atresia on academic performance in children. The Laryngoscope, 123(9), 2270–2275.
  4. Jensen, D. R., Grames, L. M., & Lieu, J. E. C. (2013). Effects of Aural Atresia on Speech Development and Learning. JAMA Otolaryngology–Head & Neck Surgery, 139(8), 797.
  5. Kuppler, K., Lewis, M., & Evans, A. K. (2013). A review of unilateral hearing loss and academic performance: Is it time to reassess traditional dogmata? International Journal of Pediatric Otorhinolaryngology, 77(5), 617–622.
  6. Lieu, J. E. C. (2004). Speech-language and educational consequences of unilateral hearing loss in children. Archives of Otolaryngology–Head & Neck Surgery, 130(5), 524–530.
  7. Lieu, Judith E Cho; Tye-Murray, Nancy, Fu, Q. (2012). Longitudinal study of children with unilateral hearing loss. Laryngoscope, 122(9), 2088–2095.
  8. Jahrsdoerfer RA, Yeakley JW, Aguilar EA, et al. Grading system for the selection of patients with congenital aural atresia. Am J Otol. 1992; 13: 6-12
  9. Roberson, J. B. J., Reinisch, J.. (2009). Atresia repair before microtia reconstruction: comparison of early with standard surgical timing. Otology & Neurotology. 30(6), 771–776.
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