Identification of Posterior Facial Asymmetry With Submento-Vertex Cephalogram Analysis

Objectives: There are various kinds of craniofacial asymmetry and numerous methods of measuring the craniofacial skeleton. We have identified a subset of patients undergoing orthognathic surgery for correction of jaw deformation malocclusion that have only minor facial asymmetry when viewed from the dental midlines on a posterior-anterior cephalagram, yet pronounced asymmetry of the posterior nasal spine (PNS) and no history of trauma, termed posterior facial asymmetry (PFA). Genetically, these subjects have down-regulation of the nodal signaling pathway, indicating strong genetic influence on development of this unusual phenotype. This study developed a method to identify and measure posterior facial asymmetry using a submento-vertex cephalogram (SMVC).

Methods: SMVCs of 45 pre-surgical patients with jaw-deformation malocclusion, but without significant facial or dental midline asymmetry deviations, were evaluated using the Ritucci and Burstone SMVC cephalometric analysis. The anatomical locations PVP (Posterior Vomer Point) and AVP (Anterior Vomer Point) were used in conjunction with an angle PVPA (Posterior Vomer Point Angle) to quantify the deviation of the posterior nasal septum. PVPA was created between a line perpendicularly bisecting the Foramen Spinosa (FS), designated FS Axis, and PVP. Linear and angular measurements were traced and analyzed using the program imageJ.


Results: Twenty four (53.3%) subjects were found to have moderate to severe PFA, as indicated by greater than 15° deviation of the PVP. Subjects without PFA had a mean PVPA of 5.6 + 4° and those with PFA 40+14.47°. A t-test found these differences to be very significant at p=0.001.

Conclusions: PFA can be easily and routinely identified on SMV cephalometric projections, and is almost undistinguishable on more standard lateral and posterior-anterior cephalograms. The prevalence of PFA in dentofacial deformity patients undergoing orthognathic surgery to correct malocclusion are quite high, but until now mostly undiagnosed as a craniofacial condition. Future research should seek clinical relevance of this posterior facial asymmetry.