Hemifacial Microsomia

Definition of Hemifacial Microsomia

Hemifacial microsomia is a congenital condition characterised by a spectrum of underdeveloped facial features. It is the commonest craniofacial abnormality^​3 and usually occurs from sporadic mutations⁴ that affect the first and second branchial arches.

Other names for hemifacial microsomia include First and Second Brachial Arch Syndrome, Otomandibular Dysostosis, Craniofacial Microsomia, or the oculoauriculovertebral spectrum. It correlates with Tessier Craniofacial Cleft 7.

Clinical Features of Hemifacial Microsomia

Hemifacial microsomia is a clinical diagnosis. It is usually a unilateral condition but can be bilaterally asymmetric. There is a variable phenotype, which means the clinical features are part of a spectrum of severity.

"Classic" Clinical Features

• Ear underdevelopment: microtia, anotia, atresia.
• Hypoplasia of the bone: mandible, zygoma, maxilla, temporal bone.
• Muscle underdevelopment: mastication, palatal, tongue.

Associated pathologies

• Cleft Palate: ~35% incidence in hemifacial microsomia^​7​
• Facial Nerve Dysfunction: ~22% incidence^​8​  ± absent parotid gland.
• Macrostomia: ~23% incidence in hemifacial microsomia^​9​

Classification of Hemifacial Microsomia

Multiple classification systems for hemifacial microsomia exist. This is to overcome the heterogeneity of clinical appearances from this condition.

OMENS Classification for Hemifacial Microsomia

This classifies deformities based on Orbits, Mandible, Ear, Nerve (Facial) and Soft Tissue^​10. Unlike other classifications, this encompasses the clinical spectrum of the condition.

Pruzansky Classification of the Mandible

The Pruzansky classification assesses the degree of mandibular involvement in hemifacial microsomia. Most commonly, there is an asymmetric mandible with only unilateral involvement.

• I: Mild ramus hypoplasia; the body is minimally affected.
• IIa: Ramus & condyle hypoplasia, the glenoid-condyle surface is normal.
• IIb: Type IIa and a non-articulating TMJ.
• III: Thin or absent ramus and no TMJ.

Meurman Classification of the Ear

The Meurman classification assesses the degree of auricle involvement in hemifacial microsomia. There are 3 grades based on the presence or absence of structures.

• I: Small ear with all structures present.
• II: cartilage and skin remnant, atresia of the external meatus
• III: total or near-total absence of the ear.

Management of Hemifacial Microsomia

There is no standardised treatment algorithm for hemifacial microsomia. This is primarily due to the phenotypic variation of patients. Current evidence-based practise promotes individualised patient care.

Minor Interventions

• Skin Tags: remove skin tags at an appropriate age. Pre-auricular skin tags with cartilage remnants may be near the facial nerve.
• Deafness: fit hearing aids as an infant to ensure no speech delay.
• Teeth: orthodontic treatment as a child and early adolescents.

Microtia

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 used^​11,12.

Mandibular Hypoplasia

There is no standardised algorithm for the timing of surgical management of mandibular hypoplasia. Traditionally, surgeons have waited until skeletal maturity to correct malocclusion with orthognathic procedures^​13,14.

• In severe cases, early mandibular distraction can be considered^​15​ to allow for appropriate bone stock development.
• In Pruzansky III, mandibular reconstruction may require a costochondral rib graft, bone grafts, and alloplastic implants.

Facial Paralysis

Management of these patients should be at centres that specialise in facial reanimation surgery. Ocular protection from corneal desiccation and ulceration is a priority.

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