Trigonocephaly

The first theory assumes that the origin of pathological synostosis lies within disturbed bone formation early on in the pregnancy. Causes can either be genetic[3][4][5][6] (9p22–24, 11q23, 22q11, FGFR1 mutation),[7] metabolic[8] (TSH suppletion in hypothyroidism)[9][10] or pharmaceutical[11] (valproate in epilepsy).[12][13]

The second theory says that synostosis begins when the fetal head gets hindered in the pelvic outlet during birth.[14][15]

The third theory predominates disturbed brain formation of the two frontal lobes as the main issue behind synostosis.[16][17][18] Limited growth of the frontal lobes leads to an absence of stimuli for cranial growth, therefore causing premature fusion of the metopic suture.

Trigonocephaly in two cases of microcephaly

Other conditions and syndromes with trigonocephaly include:

• Arthrogryposis, cleft palate, craniosynostosis, and impaired intellectual development
• Atypical glycine encephalopathy
• Blepharophimosis-intellectual disability syndrome, Verloes type
• Bohring-Opitz syndrome
• Coffin-Siris syndrome
• Greig cephalopolysyndactyly syndrome
• Holoprosencephaly
• Mandibulofacial dysostosis-microcephaly syndrome
• MEGF8-related Carpenter syndrome
• Microcephaly, primary autosomal dominant
• Mucolipidosis type II
• Orofaciodigital syndrome type 14
• Paris-Trousseau thrombocytopenia
• Potocki-Lupski syndrome
• Simpson-Golabi-Behmel syndrome type 1
• Trichothiodystrophy, photosensitive
• Trigonocephaly-bifid nose-acral anomalies syndrome

A form of surgery is the so-called fronto-supraorbital advancement and remodelling.[33] 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.

The so-called 'floating forehead technique'[2] 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.[34][35] 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.[36]

• Suturectomy[2]

The simplest form of surgery for trigonocephaly was suturectomy.[37][21][34][38][39] However, as this technique was insufficient to correct the deformities, it is not used anymore.

• Distraction osteogenesis[2]

Distraction osteogenesis is based on creating more cranial space for the brain by gradually moving the bones apart. This can be achieved by using springs.[40]

• Minimal invasive endoscopic surgery[2]

These 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.

Trigonocephaly seems to be the most compliant form of craniosynostosis for surgery.[22] Because of standardization of current surgical approaches there is no surgical mortality and complications are few to none.[2][41][42] The simple suturectomy is presently insufficient to adjust the complicated growth restrictions caused by metopic synostosis.[2] On the other hand, the fronto-supraorbital advancement and remodelling and the 'floating forehead technique' create sufficient space for brain growth and result in a normal horizontal axis of the orbits and supraorbital bar. The fronto-supraorbital advancement and remodelling is the most used method nowadays.[41] Over the past few years distraction osteogenesis has been gradually acknowledged since it has a positive effect on hypotelorism. Expanding the distance between the orbits using springs seems to be successful.[2][43][44][45] However, there are discussions whether hypotelorism really needs to be corrected.[46] The minimal invasive endoscopic surgery has been gaining attention since the early '90s, however, it has technical limitations (only strip craniectomy is possible).[2] Attempts have been made to reach beyond these limits.[47][48][49][50][51]

Aesthetic outcome of metopic synostosis surgery is persistently good with reoperation hazards below 20%.[52][53] In 1981 Anderson advised that craniofacial operations for synostosis should be as extensive as necessary after a study of 107 cases of metopic and coronal synostosis.[21] Surgery does not provide a 100% natural outcome, mostly there will be minor irregularities. Reoperations are usually performed on more severe cases (including syndromic metopic synostosis). The hypotelorism and temporal hollowing are the most difficult to correct: the hypotelorism usually remains under corrected and a second operation is often needed for correction of temporal hollowing.[52][54]

The highest rate of neurological problems of single suture synostosis are seen in patients with trigonocephaly.[2] Surgery is performed generally before the age of one because of claims of better intellectual outcome.[27][28][20][21][22][29][30][31][32] Seemingly surgery does not influence the high incidence of neurodevelopment problems in patients with metopic synostosis. Neurological disorders such as ADHD, ASD, ODD and CD are seen in patients with trigonocephaly. These disorders are usually also associated with decreased IQ. The presence of ADHD, ASD and ODD is higher in cases with an IQ below 85. This is not the case with CD which showed an insignificant increase at an IQ below 85.[2]