Classification of trigonocephaly in metopic synostosis

The orbitofrontal deformity in metopic synostosis is recognized clinically but has not been quantitatively defined in a large patient population. The authors' purpose was to document the dysmorphology in metopic synostosis and define subtype gradations.

Demographic and computed tomographic information was recorded. Three-dimensional computed tomographic renderings were created digitally. Craniometric analysis was conducted for endocranial bifrontal angle, interzygomaticofrontal suture and interdacryon distance, and angle of orbital aperture to the midline.

Thirty-five computed tomographic scans were analyzed: 25 affected infants (median age, 5 months) and 10 controls (median age, 6 months). The endocranial bifrontal angle ranged from 100 to 148 degrees in metopic patients and 134 to 160 degrees in controls. The metopic group was split into severe metopic (100 to 124 degrees) and moderate metopic (124 to 148 degrees) synostosis. The endocranial bifrontal angle was significantly different among severe metopic, moderate metopic, and control patients. Interzygomaticofrontal suture of the severe group was less than in both moderate (p = 0.0043) and control (p = 0.011) groups. Interdacryon distance was smaller in severe versus moderate (p = 0.0083) and control (p = 0.0002) groups. The orbital rim angle of the severe group was more acute than that in the moderate (p = 0.0106) and control (p = 0.0062) groups. Except for endocranial bifrontal angle, there was no difference between moderate metopic and control groups in any analysis.

Metopic synostosis can be divided into two distinct severity indices. The severe group has significantly narrower orbitofrontal dimensions, whereas the moderate group does not differ from control. Characterization of trigonocephaly may shed light on the etiopathogenesis of disease.