Hemifacial microsomia is a congenital disorder that affects the development of the lower half of the face, most commonly the ears, the mouth and the mandible. It can occur on one side of the face or both. If severe it can lead to difficulties in breathing, obstructing the trachea and requiring a tracheotomy. It is the second most common facial birth defect after clefts, with an incidence in the range of 1 in 3500 to 4500. Hemifacial microsomia shares many similarities with Treacher Collins syndrome.
The condition is also known by various other names:
- Lateral facial dysplasia
- First and second branchial arch syndrome
- Oral-mandibular-auricular syndrome
- Otomandibular dysostosis
- Craniofacial microsomia
The condition develops during the fetal stage of pregnancy at approximately 4 weeks of gestation, when some form of vascular problem leads to clotting and a poor supply of blood to the face. This can be caused by a physical trauma, though there is some evidence of it being hereditary . This restricts the developmental ability of that area of the face. Currently there are no definitive reasons for the development of the condition.
The clinical presentation of hemifacial microsomia (HFM) can be quite variable. In some children, just the ear is affected (microtia or a small, underdeveloped ear), and in other children, multiple parts of the face and body can be affected. While there is no grading scale that is in use universally, the OMENS scale (standing for Orbital, Mandible, Ear, Nerves and Soft tissue) was developed to help describe the heterogeneous phenotype that makes up this malformation. Children with HFM are at higher risk for hearing loss, and should have their hearing tested. A proportion of children with HFM will have extra-cranial anomalies, including abnormalities of the kidneys and cervical spine, which are important to detect early in childhood. Cognition and development is usually typical in children with HFM.
Some have hypothesized that the severity of hemifacial microsomia depends on the extent of the physical injury (the area with a short supply of blood) and the gestational age of the fetus – the earlier the injury, the greater the chance of wide-scale problems. This has not yet been proven in an animal or human model.
Pruzanksky classified Hemifacial Microsomia patients into three different types.
- Type I : Mild hypoplasia of the ramus , and the the body of the mandible is slightly affected.
- Type II : The condyle and ramus are small, the head of the condyle is flattened , the glenoid fossa is absent , the condyle is hinged on a flat, often convex, infratemporal surface , the coronoid may be absent.
- Type III: The ramus is reduced to a thin lamina of bone or is completely absent. There is no evidence of a TMJ.
Depending upon the treatment required, it is sometimes most appropriate to wait until later in life for a surgical remedy – the childhood growth of the face may highlight or increase the symptoms. When surgery is required, particularly when there is a severe disfiguration of the jaw, it is common to use a rib graft to help correct the shape.
According to literature, Hemifacial Microsomia patients can be treated with various treatment options such functional therapy with an appliance, Distraction osteogenesis, or Costochondral Graft. The treatment is based on the type of severity for these patients. According to Pruzanksky's classification, if the patient has moderate to severe symptoms, than surgery is preferred. If patient has mild symptoms, than a functional appliance is generally used. 
Patients can also benefit from a Bone Anchored Hearing Aid (BAHA).
- Hansen, PR (1999). "Orthodontic management of the patient undergoing mandibular distraction osteogenesis.". Seminar in Orthodontics. Retrieved 21 September 2015.
- ^ "Hemifacial Microsomia" at the Tennessee Craniofacial Center. Accessed 20 January 2008.
- ^ "Hemifacial Microsomia" at the Children's Hospital and Health System of Wisconsin. Accessed 20 January 2008.