Hemifacial microsomia (HFM) is the second most common congenital facial anomaly after cleft lip/palate. The condition may vary from mild to severe. Goldenhar syndrome has been described as a variant of hemifacial microsomia, in which vertebral anomalies and epibulbar dermoids are present.
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Terminology
Hemifacial microsomia is also known as craniofacial microsomia, first and second branchial arch syndrome, otomandibular dysostosis, and lateral facial dysplasia.
Epidemiology
Associations
As many as 55% of patients with hemifacial microsomia also have extracranial anomalies, which may include central nervous system (CNS), skeletal, cardiac, lung, gastrointestinal, and kidney defects 3,4.
Pathology
Hemifacial microsomia results from the abnormal development of the first and second branchial arches, hence it primarily affects the ear (aural), mouth (oral cavity), and jaw (mandible).
Classification
A classification that grades mandibular deficiency was developed by Pruzansky in 1969 5:
grade I: minimal hypoplasia of the mandible
grade II: functioning but deformed temporomandibular joint with anteriorly and medially displaced condyle
grade III: absence of the ramus and glenoid fossa
Radiographic features
CT is the usual imaging modality of choice to assess the extent of microsomia. There are a number of features:
ear: hypoplasia, aplasia, or malformation of the external ear and middle ear; there may be a hypoplastic mastoid process with partial or complete lack of pneumatization of the mastoid air cells
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mandible: hypoplastic mandibular condyle, reduced height of the mandibular ramus with the chin deviated towards the affected side
the temporomandibular joint deformity can range from mild hypoplasia of the condyle with normal joint anatomy to a grossly disorganized joint anatomy and pseudo-articulation of the condyle at the cranial base
maxilla: may be normal or reduced in height with delayed eruption of the mandibular and maxillary molars
zygoma: may be hypoplastic with short or absent zygomatic arch
orbit: may be reduced in dimensions and the frontal bone can be flattened
soft tissues: facial musculature, facial nerve supply, and other adjacent soft tissues may be hypoplastic
The CT dataset may also be used to produce 3D models using advanced printing techniques popular for pre-surgical planning.
Differential diagnosis
Pierre Robin syndrome: micrognathia, glossoptosis, and cleft palate
Treacher Collins syndrome: hypoplasia of facial bones, especially malar and mandibular bones, malformation of the external, middle, and internal ear, macrostomia, and high palatal arch
Parry-Romberg syndrome (facial hemiatrophy): progressive wasting of subcutaneous fat, sometimes accompanied by atrophy of skin, cartilage, bone and muscle