Hemifacial Microsomia: Use of the OMENS- Plus Classification at the Royal Children’s Hospital of Melbourne Christopher C.-H. Poon, M.B.B.S., B.D.Sc., John G. Meara, M.D., D.M.D., and Andrew A. C. Heggie, M.B.B.S., M.D.Sc., F.R.A.C.D.S.(O.M.S.), F.F.D.R.C.S. Melbourne, Australia Hemifacial microsomia is the most common facial con- genital disability after cleft lip and palate, but as yet its pathogenesis remains unknown. Clinical classification sys- tems have evolved over the last 30 years from those clas- sifying only single components of the disorder, to those classifying according to the combination of deformities, to the most recent systems that grade each anatomical com- ponent separately, such as the Orbit, Mandible, Ear, Nerve, and Soft tissue (OMENS) system. The aim of the present study was to review the classification of patients with hemifacial microsomia treated by the Melbourne Craniofacial Unit at the Royal Children’s Hospital using the OMENS-Plus system of classification and to correlate the findings with data from other centers. Records of patients treated by the craniofacial unit were reviewed and included in the study if adequate clinical records, photographs, and radiographs (anteroposterior, lateral, basal cephalometry, panoramic views) were avail- able. The data were entered into a database file developed for this purpose. Seventy-one patients were identified from the hospital database, of which six were excluded because of incom- plete data. Of the 65 patients, there were 31 (48 percent) with right-sided microsomia, 25 (38 percent) with left- sided microsomia, and nine (14 percent) with bilateral microsomia, with an overall male-to-female ratio of 1.2:1. The majority of patients had a normal orbit (77 percent), mildly hypoplastic mandibular ramus-condyle with func- tioning temporomandibular joint (57 percent with type M1 or M2a), normal facial nerve (76 percent), and mild soft-tissue hypoplasia (73 percent). There was a similar proportion of patients with mild ear anomalies (53 per- cent with grade 0 or 1) compared with those with more severe anomalies (47 percent with grade 2 or 3). Correl- ative analysis demonstrated a slight but positive correla- tion between the severity gradings of the five individual components. The correlation was lowest between the grading of the nerve and ear and that of the mandible and nerve. The data demonstrate the phenotypic variability of hemifacial microsomia and suggest a degree of relation- ship among the components of hemifacial microsomia. The OMENS-Plus system has provided a major advance- ment in the classification of hemifacial microsomia. The authors suggest refinements to the grading of the orbit and nerve components. (Plast. Reconstr. Surg. 111: 1011, 2003.) Hemifacial microsomia is a common term used to describe a sporadic complex spectrum of congenital anomalies that primarily involve the skeletal and soft-tissue components derived from the first and second pharyngeal arches. Although there are no universally agreed on minimum diagnostic criteria, the facial pheno- type, which is predominantly characterized by asymmetrical hypoplasia of the facial skeleton, the ear, and facial soft tissues, is often distinc- tive enough to differentiate from other cranio- facial conditions. It is the most common facial congenital disability after cleft lip and palate, with an estimated frequency of about 1 in 5600 births. 1 A variety of terms have been used to describe the broad spectrum of phenotypes that exist. The term hemifacial microsomia was first used by Gorlin et al. 2 and can be misleading because it implies the condition is unilateral and does not involve the cranium. Although the majority of cases involve only one side, bilateral cases occur in 30 percent of patients. Other terms include craniofacial microsomia, 3 otomandibu- lar dysostosis, 4 first and second branchial arch syndrome, 1,5 oculoauriculovertebral dysplasia, 2 Goldenhar syndrome, 6,7 and lateral facial dys- From the Craniofacial Unit, Royal Children’s Hospital. Received for publication November 21, 2001; revised May 28, 2002. DOI: 10.1097/01.PRS.0000046245.44567.D6 1011