Hemifacial microsomia: clinical features and pictographic representations of the OMENS classification system.

Learning Objectives: After reviewing this article, the participant should be able to: 1. Describe the fundamental malformations defining hemifacial microsomia. 2. Distinguish hemifacial microsomia from other congenital craniofacial anomalies sharing similar features. 3. Understand the variety of systems developed to clinically classify the features of this disorder. 4. Describe the format of the OMENS clinical classification system and appreciate its possible advantages and limitations.

Background: The clinical manifestations of hemifacial microsomia comprise a spectrum that is both broad and complex. The fundamental features include unilateral hypoplasia of the craniofacial skeleton and its overlying soft tissue. Numerous schemes have been developed to classify this spectrum. One of the most recent classification systems, the OMENS system, scores five clinical manifestations of hemifacial microsomia according to dysmorphic severity on a scale from 0 to 3: orbital asymmetry, mandibular hypoplasia, ear deformity, nerve dysfunction, and soft-tissue deficiency.

Methods: The authors describe the diverse features of hemifacial microsomia and the numerous attempts at its clinical classification, with particular emphasis on the OMENS system.

Results: With the possible exception of the OMENS scheme, the various systems developed to classify the clinical features of hemifacial microsomia fail to possess the flexibility and versatility needed to categorize all potential phenotypes of this complex disorder.

Conclusions: The OMENS system represents the most comprehensive, versatile, objective, and easily adaptable attempt at clinical classification of hemifacial microsomia to date. The authors propose a concise clinical evaluation form using a modified version of the system to promote the use of the OMENS system, to aid in the evaluation of hemifacial microsomia patients, and to assist in data sharing among academic institutions.