MedGen

Hemifacial myohyperplasia (HFMH) is a rare cause of facial asymmetry exclusively involving facial muscles (summary by Bayard et al., 2023). [from OMIM]

A malformation syndrome involving the abnormal growth of the facial skeleton as well as its soft tissue structure and organs. The syndrome has characteristics of mild facial asymmetry with unaffected neurocranium and eyeballs, along with esotropia, amblyopia and/or convergent strabismus and occasionally submucous cleft palate. Transmission is autosomal dominant. There have been no further descriptions in the literature since 1979. [from SNOMEDCT_US]

The criteria for the hemifacial type of congenital hypertrophy are (1) unilateral enlargement of the viscerocranium bounded superiorly by the frontal bone (not including the eye), inferiorly by the inferior border of the mandible, medially by the midline of the face, and laterally by the ear, the pinna being included within the hypertropic area, and (2) enlargement of all tissues--teeth, bone, and soft tissue--within this area (Rowe, 1962). [from OMIM]