The incidence of anterior belly of digastric agenesis in patients with hemifacial microsomia.

BACKGROUND

: The study examined the incidence of anterior belly of digastric muscle agenesis in patients with hemifacial microsomia, to determine the need for routine imaging of the floor of the mouth in patients within this group requesting dynamic lower lip reanimation.

METHODS

: Patients presenting with microtia were assessed according to the OMENS [orbital deformity, mandibular hypoplasia, ear deformity, nerve (cranialnerve VII) involvement, and soft-tissue deficiency] criteria, and also imaged to establish the presence or absence of the anterior belly of the digastric muscle. Each affected hemiface was treated as an individual case (n = 50), with unaffected hemifaces being assigned as controls (an additional group of unaffected controls were also included). The hemifaces with microtia were then subdivided into three groups: those with isolated microtia (with anterior belly of the digastric muscle present), those with features consistent with hemifacial microsomia (with the anterior belly of the digastric muscle present), and those with absent anterior belly of the digastric muscle.

RESULTS

: Anterior belly of the digastric muscle agenesis rate was 40 percent in those patients displaying features consistent with hemifacial microsomia. Median OMENS scores were significantly different in intergroup analysis (p < 0.0001), with a trend noticed between the median value for the hemifacial microsomia group and those with absent anterior belly of the digastric muscle. There were no noted incidences of anterior belly of the digastric muscle agenesis in the control group.

CONCLUSIONS

: The incidence of anterior belly of the digastric muscle agenesis in patients with hemifacial microsomia is high. Before any attempt to undertake lower lip reanimation using this muscle, the floor of the mouth should be imaged to check for its presence.