Hemifacial Microsomia (HFM) is a congenital condition affecting first and second branchial arch derivatives. It is characterized by a wide spectrum of craniofacial anomalies that vary greatly in range and severity among affected individuals, involving the eyes, ears, cheekbones, jaw, mouth, and/or bones of the spinal column (vertebra). Although, most cases (approximately 70%) are unilateral, bilateral cases are also observed with one side typically more affected than the other (asymmetry). In the majority of such cases, the right side is more severely affected than the left. In addition to craniofacial anomalies, cardiovascular, genitourinary, pulmonary, and nervous system can also be affected. In 48% of the cases, the condition is a part of a larger syndrome such as Goldenhar syndrome. The clinical picture of the HFM is more severe in Goldenhar syndrome. Surgical treatment is used to correct the jaw on the affected side, to rebuild the outer ear, and to build up the cheeks.
HFM is the second most common craniofacial malformation after cleft lip and cleft palate. Etiology of the condition remains unclear. However, it seems to be a multifactorial disease because different factors such as ingestion of some drugs (cocaine, thalidomide, retinoic acid, tamoxifen), environmental factors (insecticides, herbicides), and maternal diabetes were supposed to be involved in the development of the disease. The incidence of this disease is estimated at one in every 5,600 live births, with more affected male patients than females.
Most cases of HFM are sporadic. The pattern of inheritance in the familial cases is autosomal dominant. However, autosomal recessive inheritance was reported in few families.