Microtia is a congenital hypoplastic malformation of the ear. This article details the assessment, classification, and surgical management of microtia.
A syndromic or isolated congenital hypoplastic deformity that presents in a clinical spectrum from minor to complete absence.
The first and second branchial arches develop into six Hillocks of His. These develop the ear during the 5-9th weeks of gestation.
Classified by the number of vestigial ear structures present.
Hearing loss, bone hypoplasia, systemic soft tissue pathology and craniofacial syndromes.
Definition of Microtia
Microtia is a congenital hypoplastic deformity that can occur in isolation or in a syndrome. It presents a clinical spectrum of minor deficiencies to the complete absence of the auricle
Major research and surgical development was performed by Tanzer in the second half of the 20th century.
Multiple causes have been suggested. These include genetics, teratogens, and vascular abnormalities/ischemia1. These embryological abnormalities are relatively rare.
- Prevalence is approximately 1-2 per 10,0000 births2-4
- Male predominance
- Ratio of right/left/bilateral is 5:3:14
Embryology of Microtia
The first and second branchial arches develop into six Hillocks of His. This leads to ear development during the 5-9th weeks of gestation.
Microtia occurs during the embryological development of the first (mandibular) and second (hyoid) pharyngeal (branchial) arches. More specifically, the six hillocks of His.
Important embryology structures to consider are:
- Ectoderm: helps differentiate mesoderm into cartilage & forms the inner ear.
- 1st & 2nd pharyngeal arches: give 3 ant. & post. hillocks, respectively.
- 1st pharyngeal cleft: forms the external auditory meatus.
- 1st pharyngeal pouch: develops into the middle ear and Eustachian tube
- Anterior hillock: lower forms tragus, middle from crus of helix, upper forms majority of the helix.
- Posterior hillock: lower forms lobule and lower helix, middle forms antitragus, upper forms antihelix.
Microtia severity depends on the timing. An earlier embryological issue results in a more severe presentation. Important dates to consider are:
- Week 5: External ear begins to form.
- Week 6: anterior and posterior hillocks form.
- Week 9: ear becomes recognisable.
Clinical Features of Microtia
Microtia is a clinical spectrum that is classified based on the number of vestigial ear structures present.
Microtia is a clinical spectrum of severity that can be syndromic or occur in isolation (more common)1. It is graded in accordance with the number of vestigial ear structures present.
- Anotia: the 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.
This is illustrated in the diagram below.
Microtia is just one aspect of congenital ear deformities. The entire spectrum of "congenital ear deformities" (which includes microtia) was published by Tanzer.
- Type 1: Anotia
- Type 2: Complete hypoplasia (microtia)
- Type 2A: Microtia with atresia of the external auditory meatus
- Type 2B: Microtia without atresia of the external auditory meatus
- Type 3: Hypoplasia of the middle-third of the ear
- Type 4: Hypoplasia of the superior-third of the ear.
- Type 4A: Constricted ear – lop/cup/pixie
- Type 4B: Cryptotia
- Type 4C: Hypoplasia of the entire upper third of the ear
- Type 5: Prominent Ear
Secondary Features of Microtia
Microtia is associated with hearing loss, bone hypoplasia, systemic soft tissue pathology and craniofacial syndromes.
Hearing loss in microtia is ~15% sensorineural and ~85% conductive. There can also be mixed (sensorineural and conductive)7. It is associated with:
- Ossicles: disrupted or absent
- External Auditory Canal: stenosis (linked to mixed hearing loss and risk of cholesteatoma) or atresia (linked to a conductive hearing loss) 5
- Loss of tympanic cavity
Hearing loss and atresia can be treated through different techniques
- Bone-anchored hearing aid (BAHA) abutment placed >65mm posterior to the external auditory meatus to avoid scars on the non-hair bearing mastoid skin. It can be placed after external ear reconstruction in unilateral cases.
- Meatoplasty/Canaloplasty: not routinely performed due to mild hearing improvement, risk of facial nerve injury.
- Middle ear implants
The severity of external deformities correlates with the severity of temporal bone abormalities1. Bone pathology can include:
- Mandibular hypoplasia (commonly the condyle)
- Temporal bone
- Limb reduction defects
- Head and Neck: Facial nerve pathology, Cleft lip and palate
- Cardiac Defects
- Eye: Anophthalmia and microphthalmia
- Renal: syndromic ear anomalies are associated with brachio-oto-renal syndrome and Townes-Brocks syndrome. Ultrasound of the kidneys should be considered.
It is suggested to be the mildest form of hemifacial microsomia2-3. It is also linked to other syndromes such as:
Investigations for Microtia
All microtia patients should undergo complete radiological and audiological evaluation, regardless of presentation.
- CT: show temporal bone & middle ear, ossicles, cholesteatoma (squamous epithelium trapped in the middle ear)
- MRI: show facial nerve (often displaced in middle ear malformations6,7)
In terms of audiometric testing, this will determine conductive vs sensorineural hearing loss.
Management of Microtia
The surgical treatment of microtia is centred on autologous, alloplastic or prosthetic materials through two common techniques: Brent or Nagata. The number goal is to restore hearing, followed by reconstruction.
The management of microtia should focus on the patient's goals, the timing of intervention, and surgical options in a multi-disciplinary team. Reconstruction is usually around the age of 7 - at this stage, the patient's ear size is suitable, donor site cartilageis suitable and the patient can often help make an informed decision.
The primary goal of microtia management is to improve acoustic function. Other goals to consider are:
- Preservation of the normal ear
- Improve the affected one
- Enable speech development
- 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? Emotion and psychological factors, particularly in young school kids, are important considerations.
- Is Middle Ear Surgery required? 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 the facial nerve, but it can improve hearing by 70% in some cases9-10.
The material options can be classified into autologous, alloplastics or bone-anchored prostheses. Staged autogenous cartilage reconstruction remains the gold standard to correct microtia.
- Autologous Cartilage Graft: creation of a "cartilage rib framework" through multiple-stage techniques. This was popularised by Brent (4 stages) and Nagata (2 stages).
- Bone-anchored Prosthesis: two-stage radiologically-guided osseointegration, discovered by Brånemark.
- Alloplastic: single-stage subcutaneous implantation, often Medpor, via the Reinisch technqiue. Less commonly used due to the higher rates of extrusion.
The two commonly performed microtia techniques are described by Brent and Nagata. They differ in their stages, the timing of surgery and surgical steps.
- Brent11: 4-stage reconstruction is commonly performed between 4-6 years and is resurfaced with postauricular scalp advancement. Lobule elevation/creation and tragus reconstruction occur at different times.
- Nagata Technique12: 2-stage reconstruction starting at the age of 10 and is resurfaced with temporoparietal fascial flap.
The temporoparietal fascial flap is based on the superficial temporal vessels and is traditionally considered a "workhorse flap" in ear reconstruction. Other soft tissue coverage options include a galeal flap, which has better scarring than the temporopartietal fascial flap.
After a 5-year follow-up, Brent concluded11:
- 48% grow at the same rate as normal ears
- 46% grow slight bigger
- 10% grow slightly smaller.
For a detailed review of surgical techniques, check out these CME PRS Publications.
Other Auricular Abnormalities
Other auricular abnormalities to consider include Stahl's ear, cryptotia, and constricted ear.
- An abnormal third crus traverses the superior third of the ear (from the crus antihelix to the edge of the helix).
- The appearance of a "flattened" helix
- It can be treated with neonatal moulding.
- The upper pole of the helix is buried beneath the temporal skin
- Less common findings can include missing upper sulcus, underdeveloped scapha or antihelical crura.
- Reconstruction aims to create a posterior sulcus with a skin graft or flap.
- Cause is due to an anomaly of intrinsic oblique and transverse auricular muscles.
- A deficiency in the "circumference of the helix"
- Lop ear: folding of the superior aspect of the helix
- Cup ear: folding of the superior aspect of the helix and a prominent ear.
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