Microtia

Microtia is a congenital hypoplastic malformation of the ear. This article details the assessment, classification, and surgical management of microtia.

In this Microtia Article

1. Definition
2. Embryology
3. Clinical Features
4. Investigations
5. Decision-Making
6. Surgical Techniques
7. References

Definition of Microtia

Microtia is a congenital hypoplastic malformation of the ear. The condition is a spectrum ranging from subtle deficiencies to complete abscence of the auricle.

Major research and surgical development was performed by Tanzer in the second half of the 20th century.

Embryology of Microtia

Microtia occurs due to a broad range of deformities involving the first and second branchial arches.

The ear is developed from the first (mandibular) and second (hyoid) branchial arches. More specifically, the six hillocks of His.

Failure of this development at 6-8 weeks of gestation can lead to microtia. The earlier the adverse development, the more severe the microtia. This is why it is often referred to as a spectrum. Multiple causes have been suggested. These include¹:  

• Genetics
• Teratogens
• Vascular abnormalities/ischemia

These embryological abnormalities are relatively rare. Here are some relevant statistics:

• Prevalence is approximately 1-2 per 10,0000 births^2-4
• Estimated ratio of right/left/bilateralis 5:3:1⁴

Clinical Features of Microtia

Microtia can occur in isolation or can be associated with middle ear defects, hearing loss, syndromes, bone or nerve pathology.

The most common clinical presentation of microtia is an isolated deformity¹. This is felt to represent the mildest form of hemifacial microsomia^2-3.

Classification of Microtia

Microtia is graded in accordance with the number of vestigal ear structures present. Some surgeons and research articles refer to this as "grades" of microtia.

• Anotia: complete absence of the external ear.
• Lobule-type: remnant ear & lobule without concha, acoustic meatus & tragus.
• Concha-type: lobule, concha, acoustic meatus, tragus & incisura tragica are present to variable degrees.
• Small concha-type: remnant lobule, small indentation representing concha.
• Atypical microtia: patients who cannot be classified above.  

Associated Features

Hearing Loss

Hearing loss in microtia is ~15% sensorineural  and ~85% conductive. There can also be mixed (sensorineural and conductive)⁷.  Causes of hearing loss in microtia relate to:

• Ossicles: disrupted or absent
• External Auditory Canal: stenosis (linked to mixed hearing loss and risk of cholesteatoma) or atresia (linked to conductive hearing loss) ⁵
• Loss of tympanic cavity

Presence of a tragus has been considered an indication of middle ear function⁶

Bone

Severity of external defmoities correlates wth severity of temporal bone abormalities¹. Bone pathology can include:

• Mandibular hypoplasia (commonly the condyle)
• Temporal bone
• Vertebra.

Additional Malformations:

• Facial nerve abnormalities
• Cleft lip and palate
• Cardiac Defects
• Eye: Anopthalmia and micropthalmia

Investigations for Microtia

Essential to perform complete radiographic and audiological evaluation for every child with microtia, regardless of presentation.

In term's of Imaging:

• High-Res CT will show temporal bone and middle ear, middle ear ossicles, and exclude cholestertoma.
• MRI can help define course of facial nerve, which is often displaced in middle ear malformations^6,7

In terms of audiometric testing, this will to determine conductive vs sensorineural hearing loss.

Decision-Making

The management of microtia should focus on three aspects: the patient's goals, the timing of intervention, and surgical options.

Goals of Treatment

The goal of microtia management is for preservaton of normal ear and amplification of the affected one, enable speech development and improve aesthetics.

Timing of Microtia Surgery

The exact time for microtia surgery is reflective of the patient and surgical preference. Issues to take into consideration are:

• Is the ear developed? Most ears are developed by the age of 4 or 5. The width of the ear continues to grow until 10. It's also important to consider if there is adequate donor-site rib cartilage.
• What surgery is required? This is discussed in more detail in the next section. The Brent Technique is performed earlier than the Nagata Technique.
• Is the kid being bullied? The emotion and psychological factors, particularly in young school kids is an important consideration.
• Is Middle Ear Surgery required? If so, ideally the external ear should be treated first. Middle ear reconstruction is not indicated for unilateral microtia with normal hearing in the contralateral ear⁸. There is a risk of injury to facial nerve but can improve hearing by 70% in some cases^9-10.

Surgical Treatment of Microtia  

The surgical treatment of microtia is centred on autologous, alloplastic or prosthetic  materials through two common technqiues: Brent or Nagata.

Material Options

The material options can be classified into autologous, alloplastics or prosthetic. Each option has been developed over time and each option has it's own limitations.

• Costal Cartilage Graft: a good long-term reconstructive option first described by Tanzer. Common techniques now are Brent or Nagata.
• Prosthesis: These can be osseointegrated but can be quite expensive.
• Implant: different implants are available and generally they provide good aesthetic results and avoids a donor site morbidity issue. There are often performed as a single-stage operation.

Surgical Techniques

The two commonly performed microtia techniques are described by Brent and Nagata. They differ in their stages, timing of surgery and surgical steps.

• Brent¹¹: 4-stage reconstruction commonly performed between 4-6 years.
• Nagata Technique¹²: 2-stage reconstructon starting at the age of 10.

For a detail review of surgical techniques, check out these CME PRS Publications.

Auricular reconstruction for microtia: part I. Anatomy, embryology, and clinical evaluation - PubMed

Auricular reconstruction for microtia: part I. Anatomy, embryology, and clinical evaluation

PubMedElisabeth K Beahm

Auricular reconstruction for microtia: Part II. Surgical techniques - PubMed

Reconstruction of the microtic ear represents one of the most demanding challenges in reconstructive surgery. In this review the two most commonly used techniques for ear reconstruction, the Brent and Nagata techniques, are addressed in detail. Unique to this endeavor, the originator of each techniq…

PubMedRobert L Walton

Microtia reconstruction - PubMed

Microtia reconstruction is both challenging and controversial. Our understanding of the epidemiology and genetics of microtia is improving. Surgical techniques continue to evolve, with better results. Treatment selection continues to be controversial. There are strong proponents for reconstruction w…

PubMedGordon H Wilkes

Outcomes

Brent noticed with a minimum 5-year follow-up of reconstructed ears¹¹:

• 48% grow at same rate to normal eat
• 46% grow slight bigger
• 10% grow slightly smaller.

References

1. Llano-Rivas I, González-del Angel A, del Castillo V, Reyes R, Carnevale A. Microtia: a clinical and genetic study at the National Institute of Pediatrics in Mexico City. Arch Med Res. 1999 Mar-Apr;30(2):120-4. doi: 10.1016/s0188-0128(98)00023-2. PMID: 10372445.
2. Figueroa AA, Friede H. Craniovertebral malformations in hemifacial microsomia. J Craniofac Genet Dev Biol Suppl. 1985;1:167-78. PMID: 3877093.
3. Bennun RD, Mulliken JB, Kaban LB, Murray JE. Microtia: a microform of hemifacial microsomia. Plast Reconstr Surg. 1985 Dec;76(6):859-65. PMID: 4070453.
4. Harris J, Källén B, Robert E. The epidemiology of anotia and microtia. J Med Genet. 1996 Oct;33(10):809-13. doi: 10.1136/jmg.33.10.809. PMID: 8933331; PMCID: PMC1050757.
5. Gill NW. Congenital atresia of the ear. A review of the surgical findings in 83 cases. J Laryngol Otol. 1969 Jun;83(6):551-87. doi: 10.1017/s0022215100070687. PMID: 5785652.
6. Calzolari F, Garani G, Sensi A, Martini A. Clinical and radiological evaluation in children with microtia. Br J Audiol. 1999 Oct;33(5):303-12. doi: 10.3109/03005369909090114. PMID: 10890145.
7. Carvalho GJ, Song CS, Vargervik K, Lalwani AK. Auditory and facial nerve dysfunction in patients with hemifacial microsomia. Arch Otolaryngol Head Neck Surg. 1999 Feb;125(2):209-12. doi: 10.1001/archotol.125.2.209. PMID: 10037288.
8. David R. Moore (1986) Critical Periods for Binaural Interaction and Spatial Representation, Acta Oto-Laryngologica, 101:sup429,51-55, DOI: 10.3109/00016488609122730
9. Declau F, Cremers C, Van de Heyning P. Diagnosis and management strategies in congenital atresia of the external auditory canal. Study Group on Otological Malformations and Hearing Impairment. Br J Audiol. 1999 Oct;33(5):313-27. doi: 10.3109/03005369909090115. PMID: 10890146.
10. Chang, S.O., Min, Y.‐G., Kim, C.S. and Koh, T.‐Y. (1994), Surgical management of congenital aural atresia. The Laryngoscope, 104: 606-611. https://doi.org/10.1002/lary.5541040514
11. Brent B. Auricular repair with autogenous rib cartilage grafts: two decades of experience with 600 cases. Plast Reconstr Surg. 1992 Sep;90(3):355-74; discussion 375-6. PMID: 1513882.
12. Nagata S. A new method of total reconstruction of the auricle for microtia. Plast Reconstr Surg. 1993 Aug;92(2):187-201.
13. TANZER, R. C. (1959). TOTAL RECONSTRUCTION OF THE EXTERNAL EAR. Plastic and Reconstructive Surgery, 23(1), 1–15. doi:10.1097/00006534-195901000-00001
14. Beahm, E. K., & Walton, R. L. (2002). Auricular Reconstruction for Microtia: Part I. Anatomy, Embryology, and Clinical Evaluation. Plastic and Reconstructive Surgery, 109(7), 2473–2482.doi:10.1097/00006534-200206000-00046