Hemifacial microsomia is the second most common congenital facial anomaly after cleft lip and palate. It affects about 1 in 5,600 children. The cause of hemifacial microsomia is not known.
Children with hemifacial microsomia have an under-development of one side of the face. The effects can be very variable. Often jaws (mandible and maxilla) on the affected side are underdeveloped. Sometimes a normal jaw joint does not form. The ear may be small and abnormal (microtia) and sometimes the eye is also reduced in size. Occasionally the facial nerve is underdeveloped which causes abnormalities of movement on the affected side of the face. Soft tissues and muscles may be underdeveloped and there is often a widening of the mouth (macrostomia) on the affected side. Hemifacial microsomia is occasionally associated with other congenital anomalies such as cleft lip and palate, certain heart defects and abnormalities of the kidneys.
Specific treatment for hemifacial microsomia is variable because there are so many differences in its presentation.
Severe under-development of the jaw can cause breathing difficulties early in life and so early surgery using distraction osteogenesis (a process by which the jaw is gradually stretched to a more normal size) may be undertaken. As a rule however most surgery is delayed until later in childhood because the effects of early surgery are often undone by the abnormal growth processes associated with hemifacial microsomia.
Treatment of the mandibular and maxillary deformities often involves distraction osteogenesis, osteotomies and bone grafting. Careful orthodontic treatment is needed to ensure that a normal bite is achieved. The external ear when affected is often reconstructed at approximately 8-9 years of age. Soft tissue deficiencies may be treated by injecting fat or transferring soft tissues from other parts of the body. Treatment of severe hemifacial microsomia is often not completed until late adolescence.