Diagnosis
Diagnosis can be characterized by typical facial and cranial deformities.Observatory signs of trigonocephaly are:

a triangular forehead seen from top view leading to a smaller anterior cranial fossa
a visible and palpable midline ridge
hypotelorism inducing ethmoidal hypoplasiaImaging techniques (3D-CT, Röntgenography, MRI) show:

epicanthal folds in limited cases
teardrop-shaped orbits angulated towards the midline of the forehead (surprised coon sign) in severe cases
a contrast difference between a röntgenograph of a normal and a trigonocephalic skull
anterior curving of the metopic suture seen from lateral view of the cranium on a röntgenograph
a normal cephalic index (maximum cranium width / maximum cranium length) however, there is bitemporal shortening and biparietal broadeningThe neuropsychological development is not always affected. These effects are only visible in a small percentage of children with trigonocephaly or other suture synostoses. Neuropsychological signs are:

problems in behaviour, speech and language
mental retardation
neurodevelopmental delays such as attention deficit hyperactivity disorder (ADHD), oppositional defiant disorder (ODD), autism spectrum disorder (ASD), and conduct disorder (CD). Many of these delays become evident at school age. Treatment
Treatment is surgical with attention to form and volume. Surgery usually takes place before the age of one since it has been reported that the intellectual outcome is better. Fronto-supraorbital advancement and remodelling
A form of surgery is the so-called fronto-supraorbital advancement and remodelling. Firstly, the supraorbital bar is remodelled by a wired greenstick fracture to straighten it. Secondly, the supraorbital bar is moved 2 cm. forward and fixed only to the frontal process of the zygoma without fixation to the cranium.
Lastly, the frontal bone is divided into two, rotated and attached to the supraorbital bar causing a nude area (craniectomy) between the parietal bone and frontal bone. Bone will eventually regenerate since the dura mater lies underneath (the dura mater has osteogenic capabilities). This results in an advancement and straightening of the forehead. Floating forehead technique
The so-called floating forehead technique combined with the remodelling of the supraorbital bar is derived from the fronto-supraorbital advancement and remodelling. The supraorbital bar is remodelled as described above. The frontal bone is split in two pieces. Instead of using both pieces as in fronto-supraorbital advancement and remodelling, only one piece is rotated and attached to the supraorbital bar. This technique also leaves a craniectomy behind. Other
SuturectomyThe simplest form of surgery for trigonocephaly was suturectomy. However, as this technique was insufficient to correct the deformities, it is not used anymore. Distraction osteogenesisDistraction osteogenesis is based on creating more cranial space for the brain by gradually moving the bones apart. This can be achieved by using springs. Minimal invasive endoscopic surgeryThese approaches are 2D solutions for a 3D problem, therefore the results are not optimal. Distraction osteogenesis and minimal invasive endoscopic surgery are yet in experimental phase. Outcomes
Surgical
Trigonocephaly seems to be the most compliant form of craniosynostosis for surgery. Because of standardization of current surgical approaches there is no surgical mortality and complications are few to none. The simple suturectomy is presently insufficient to adjust the complicated growth restrictions caused by metopic synostosis.