Congenital partial absence of the facial muscles.

Facial asymmetry in a newborn infant suggests various diagnoses, including birth trauma and congenital hemifacial microsomia. But congenital absence or hypoplasia of facial muscles has not been known except for the depressor anguli oris muscle (DAOM). The authors' experience with surgical treatment of congenital hypoplasia of the risorius, zygomaticus major and minor, and levator labii superioris muscles is presented. Congenital facial muscle absence is uncommon. Although the hypoplasia of the DAOM is known, this disease is not fully clarified. The authors report a case of congenital partial palsy of the face in which some facial muscles were absent although the facial nerve was normal.