Facial asymmetry with severe unilateral hypoplasia of the muscles of mastication: a report of clinical and electromyographic findings.

Mild degrees of asymmetry of the human body have been recognised both by classical sculptors and more recently by anatomists as both normal and widely occurring. Morphologic asymmetries of the face of a more severe nature are, however, quite rare. When such deformities occur, both the hard and soft tissues may be involved and the abnormality may be acquired as a result of trauma, infection, neoplasia or surgery or be of a developmental origin as in the syndromes affecting the first pharyngeal arch. Developmental asymmetries of the jaws may also arise as a result of unilateral disruption of mandibular development during the time of normal facial growth leading to hemiretrognathism. Severe hypoplasia of the muscles of mastication on one side only has not previously been reported.