What is hemifacial microsomia? Hemifacial microsomia, proposed by Gorlin and Pindborg in 1964, is also known as hemifacial microsomia, hemicraniofacial microsomia, first and second parotid arches syndrome, auriculo-mandibular dysplasia, mandibular-facial dysplasia, unilateral facial dysplasia, etc. It is the most common congenital craniofacial abnormality after cleft lip and palate deformities, and it is mainly related to the developmental blockage of the first and second parotid arches of the fetus in the womb. It is the most common congenital craniofacial malformation after cleft lip and palate, mainly related to the obstruction of the development of the first and second parotid arches in the fetus in utero. The disease is diverse and asymmetric, and the deformities present after birth worsen with growth. The lesions are mostly unilateral, but occasionally bilateral, and involve dysplasia of the craniofacial bones, muscles, soft tissues, facial nerve, and external ear. Since the malformations may involve multiple anatomical regions and vary in severity, a comprehensive treatment plan must be developed according to the severity of the malformations. Clinical manifestations of hemifacial microsomia In the clinical manifestations of hemifacial microsomia, multiple anatomical areas can be involved with varying degrees of severity, which are characterized by facial microsomia, weak subcutaneous soft tissues, chin deviation, facial nerve hypoplasia, facial transverse fissure, and malformation of the external ear. Due to asymmetric development of the mandible, the chin tends to be skewed to the affected side, and the occlusal plane of the affected side is shifted upward. Other craniofacial skeletal involvement is related to the severity of the mandible, with dysplasia of the maxilla and zygoma on the affected side, and narrow or even absent zygomatic arches. Some patients are associated with small eyes. The frontal bone on the affected side may show flatness, similar to the manifestation of oblique head deformity. The masticatory muscles on the affected side are hypoplastic, including the biting, internal pterygoid, external pterygoid, and temporalis muscles, and the function of the muscles is impaired accordingly. The outer ear is almost always malformed to varying degrees, with preauricular dermatomes, sinus tracts, and varying degrees of abnormalities in the shape, size, and position of the outer ear in the less severe cases, or even complete absence and atresia of the external auditory canal in the more severe cases. A skin lump or sinus tract can often be seen on the cheek, and both the skin and subcutaneous tissues of the cheek can be hypoplastic, with hypoplasia or absence of the parotid gland. Treatment options Established surgical options include bone grafting, maxillary LeFort I or III osteotomy, and mandibular sagittal split osteotomy. If necessary, autologous rib cartilage or ribs are used to reconstruct the condyle and ascending ramus of the mandible. The zygomatic arch is reconstructed with autologous rib bone in case of zygomatic arch loss. In the case of hypoplasia of the infraorbital and lateral margins, a unilateral maxillary LeFort III osteotomy should be performed to move the orbital margin forward, and a contralateral LeFort I osteotomy should be performed to correct the tilt of the occlusal plane. For patients with craniofacial dysplasia involving one side, surgery should be staged, with a combined intracranial and extracranial route of anterior projection and upward displacement of the entire orbital bone in the first stage, followed by a second-stage procedure performed transorally after 6 months. The chin deviation can be corrected by horizontal chin osteotomy and molding. In addition, fat injections and dermal fat grafting or microsurgery can be used to further correct the facial asymmetry if necessary. Currently, the main option is to use mandibular lengthening to treat hemifacial shortness, and if there is an ear deformity, then the ear deformity can be corrected or even reconstructed at the same time. The specific steps of mandibular lengthening are: 1. Preoperative design based on the CT film of the mandible, i.e., according to the severity of the mandibular ascending and body deformity, choose the suitable position of the osteotomy line and lengthening direction as well as the lengthening size of the lengthening device, and the surgical guide plate can be prepared. Of course, a computerized simulation can be used to demonstrate the operation and predict the postoperative results; 2. Placement of the extender during the operation; 3. Postoperatively, the extender is used to gradually lengthen the mandible both vertically and horizontally, with the chin rotated to the healthy side. The lengthening is accompanied by the lengthening of blood vessels, nerves, skin, muscles and other soft tissues, which improves the stability of the operation. 4. The lengthening device is removed by a second operation about one year after the operation. Although mandibular lengthening can greatly improve the patient’s hemifacial shortening deformity, in order to achieve a more satisfactory result, it is still necessary to cooperate with some of the other procedures mentioned above. Of course, other facial contouring procedures performed on the basis of mandibular lengthening will be significantly less extensive and less invasive. Timing of treatment Most studies have shown that hemifacial shortening worsens with growth and development, which is relevant to the timing of treatment. Early treatment of deformed mandibles can prevent and reduce the formation and extent of secondary deformities and promote harmonious development of the craniofacial skeleton. Moreover, if the mandibular deformity can be corrected before school age, so the period is in the period of tooth replacement, the occlusal relationship can be better improved through self-adjustment during the eruption of permanent teeth. However, it is not easy to use the mandibular bone lengthening device too early, because the mandible is too small and weak for the placement of the lengthening device, and if the ear reconstruction is carried out at the same time, the small rib cartilage is not conducive to the molding of the ear bracket during the operation.