Hemifacial Microsomia

Hemifacial Microsomia

Hemifacial microsomia is the commonest craniofacial abnormality. This article details the genetics, clinical features, classifications and management.

Summary Card

Definition
The commonest craniofacial abnormality is characterised by a spectrum of underdeveloped congenital facial features.

Clinical Picture
A variable phenotype of ear, bone and muscle hypoplasia of differing severity. It is linked to cleft palate, facial nerve palsy & macrostomia.

Classification
Multiple systems exist to overcome clinical heterogeneity. This includes OMENS, Pruzansky (Mandible) and Meurman (Ear).

Management
A multi-disciplinary team to correct ocular, mandibular, ear, facial nerve and soft tissue issues over staged treatments.

Flashcards
Evidence-based flashcards to improve your active recall. 

References
Evidence-based citations from current literature and seminal papers.


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.

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Fun Fact: It is hypothesised that hemifacial microsomia may be due to a haemorrhage from an abnormal stapedial artery6 or mesodermal insufficiency5


Clinical Features of Hemifacial Microsomia


Key Point

Hemifacial microsomia is a spectrum of clinical pathology that involves the ear, bone and muscle. Each patient has a variable phenotypic appearance.


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​

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Tip: Goldenhar Syndrome is a variant of hemifacial microsomia (features of hemifacial microsomia + Tessier Cleft 8). 


Classification of Hemifacial Microsomia


Key Point

The phenotypic variability makes it difficult to classify hemifacial microsomia. Options include OMENS, Pruzansky for Mandible, and Meurman for Ear.


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.

OMENS CLasssification

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.

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Tip: The "glenoid" is an oval depression on the zygomatic process of the temporal bone that receives the condyle of the mandible.

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.

Meurman Classification


Management of Hemifacial Microsomia


Key Point

The treatment should be individualised to the patient. Key aspects include oral competence, hearing, dentition, mandibular reconstruction and facial palsy treatment, if present.


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.


Flashcards

Evidence-based flashcards are designed for active recall & spaced repetition using the Feynman Technique.

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