Hemifacial microsomia is the commonest craniofacial abnormality with significant phenotypic variability. Genetics, signs and treatment options are detailed.
In this Article
5 Key Points
The aetiology, genetics, clinical picture, and management options of Hemifacial Microsomia can be summarised in 5 key points:
- Hemifacial microsomia is the commonest craniofacial defect, which often occurs sporadically without genetic inheritance.
- There is a spectrum of phenotypic variability – as a result hemifacial microsomia has a broad clinical picture from minor skin tags to severe mandibular hypoplasia with facial nerve dysfunction.
- Hemifacial microsomia clinically correlates with Tessier Craniofacial Cleft 7.
- There are several classification systems for hemifacial microsomia, which include: OMENS, Pruzansky and Meurman.
- Management of hemifacial microsomia is centred on a disciplinary team to correct ocular, mandibular, ear, facial nerve and soft tissue issues over a prolonged period of staged treatments..
Definition of Hemifacial Microsomia
Congenital condition with variable phenotype, characterised by underdevelopment of one side of the face. It correlates with Tessier Craniofacial Cleft 7.
It also referred to as First and Second Brachial Arch Syndrome, Otomandibular Dysostosis, Craniofacial Microsomia, or oculoauriculovertebral spectrum.
Genetics of Hemifacial Microsomia
- 1 in 4000-6000 live births (commonest craniofacial abnormality)3
- Majority is sporadic mutations with seldom autosomal dominant inheritenace4.
Theories regarding the aetiology have been proposed:
- Mesodermal Insufficiency5
- May arise due to haemorrhage from an abnormal stapedial artery6
Clinical Features of Hemifacial Microsomia
Hemifacial microsomia is a clinical diagnosis. There is a variable phenotype and clinical features are part of a spectrum of severity. It is usually unilateral but can be bilateral (but still asymmetric) in about 10%.
Classic Clinical Picture
- External and middle ear underdevelopment (microtia, anotia, atresia)
- Hypoplasia of the bone (mandible, zygoma, maxilla, temporal bone)
- Underdevelopment of the muscles (mastication, palatal, tongue)
- Cleft Palate – 35% incidence in hemifacial microsomia7
- Facial Nerve Dysfunction – 22% incidence in hemifacial microsomia8 and can be associated with an absent parotid gland.
- Macrostomia – 23% incidence in hemifacial microsomia9
Classification Systems for Hemifacial Microsomia
Due to the heterogeneity of clinical appearances, multiple classifications systems for hemifacial microsomia have been published.
OMENS Classification for Hemifacial Microsomia
This classifies deformities based on Orbits, Mandible, Ear, Nerve (Facial) and Soft Tissue10.
Pruzansky Classification of the Mandible
This classification system focuses on the mandible in hemifacial microsomia. Most commonly, there is an asymmetric mandible with only unilateral involvement.
- Type 1: Mild ramus hypoplasia, the body is minimally affected.
- Type IIa: Ramus and condyle hypoplasia, but the glenoid-condyle relationship is maintained
- Type IIb: Same as type IIa but with a non-articulating TMJ
- Type III: ramus is very thing or absent with no evidence of a TMJ
In severe micrognathia, patients can suffer from Pierre Robin Sequence.
Meurman Classification of the Ear
- Grade I: Small, malformed auricle, all components are present
- Grade II: vertical remnant of cartilage and skin, atresia of the external meatus
- Grade III: Total or near-total absence of muscle.
Treatment of Hemifacial Microsomia
There is no standardised treatment algorithm for hemifacial microsomia. Due to the phenotypic variation of patients, current evidence-based medicine provides a guide that should be individualised for each patient.
This is the milder spectrum of the condition. Remove skin tags at an appropriate age. Caution of the facial nerve because the cartilage remnants can be closely associated.
If microtia is present, ear reconstruction with autologous material should be delayed until the patient is age appropriate, between 7 and 10 years, depending on the technique used11,12. Hearing aids should be fitted from an early age to ensure no speech delay.
There is no standardised algorithm for timing of surgical management of mandibular hypoplasia. Traditionally, surgeons have waited until skeletal maturity to correct malocculusion with orthognathic procedures13,14.
In severe cases, early intervention followed by mandibular distraction should be considered15This allows for appropriate bone stock so that subsequent traditional orthognathic can be attempted.
Management of these patients should be at centres that specialise in facial reanimation surgery. Ocular protection from corneal desiccation and ulceration is priority.
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