A case of orthognathic surgery for skeletal open bite with Noonan syndrome (NS)

Noonan syndrome (NS) is an autosomal dominant genetic disorder characterized by congenital abnormalities of genes involved in the intracellular Ras/MAPK signalling system. Affected individuals generally show characteristic facial features and short stature, as well as congenital heart disease, thoracic anomalies, lymphangiogenesis, and bleeding tendency. Reported here is a case of orthognathic jaw surgery performed for a 29-year-old woman with such characteristic facial features and skeletal open bite. The patient was determined to be suitable for orthognathic treatment, and examined for cardiac disease associated with NS and ability to tolerate surgery before undergoing preoperative orthodontic treatment. Le Fort I osteotomy and bilateral sagittal splitting ramus osteotomy procedures were performed under general anaesthesia. Preoperative screening revealed that platelet count and prothrombin time were normal, with only a slight increase in activated partial thromboplastin time, though the actual amount of blood loss was high at 1442 ml. While the cause of bleeding tendency associated with NS is unknown, preoperative determination of coagulation factors and platelet function, as well as screening are considered to be essential. For the present case, a bilateral sagittal splitting ramus osteotomy procedure was selected. On the other hand, because an intraoral vertical ramus osteotomy (IVRO) results in less blood loss, careful consideration should be given when choosing an orthognathic surgery technique for NS patients, such as osteotomy of the maxilla or mandible alone, or IVRO only on the side where the mandible is moved backward in cases with an asymmetrical skeletal structure.