Why do metopic sutural synostoses angulate? The concept of nasion sutural complex and its implication on the management of hypotelorism-early results and proof of concept.

Angulation at the suture is a hallmark of metopic synostoses amongst all craniosynostoses. No other sutural synostoses demonstrate angulation at synostoses consistently. We look into the possible aetiology and the implication of the understanding in the treatment goals of trigonocephaly. We hypothesise that the nasal bone and nasofrontal suture viz. "nasion sutural complex" are involved in trigonocephaly along with the well-accepted role of metopic suture. We propose that it is the angulation at this junction which leads to trigonocephaly and its secondary features. The study included seven infants, who underwent correction for trigonocephaly at our paediatric craniofacial division at Amrita Institute of Medical Sciences and Research Centre, Kochi, India, between the period July 2015 to March 2018. The cohort included were infants with trigonocephaly who had CT head for diagnosis. We analysed the multidimensional CT (MDCT) of these infants and compared to an equal number of age-matched controls. The controls were infants with other forms of sutural synostosis with metopic uninvolved and normal infants where MDCT was done for other reasons. Sutural characteristic at the nasion and metopic suture recorded in comparison with an equal number of age-matched controls. We performed spring cranioplasty for three infants after metopic suturectomy, extending the release beyond the nasion sutural complex, placing springs to distract the suture. The infants who underwent spring cranioplasty were followed up for the aesthetic outcome. Remaining infants of the study underwent standard frontorbital correction for metopic craniosynostoses. We could demonstrate a fusion of nasofrontal and nasal suture in all cases (n = 7) of trigonocephaly included in the study on MDCT and intraoperatively. We performed spring cranioplasty for three infants (n = 3/7), where we released the internasal suture. At 3 months follow-up, along with correction of the angulation, the hypotelorism improved significantly. Other infants in the study (4/7) underwent classical frontorbital advancement. Fusion of nasion sutural complex along with metopic sutures may explain the angulation in trigonocephaly. We propose that all minimally invasive techniques for correction of trigonocephaly and associated hypotelorism should consider this fact for an improved outcome.