Trigonocephaly is a congenital condition of premature fusion of the metopic suture (from the Greek , "forehead"), leading to a triangular forehead. The merging of the two frontal bones leads to transverse growth restriction and parallel growth expansion. It may occur syndromic, involving other abnormalities, or isolated. The term is from the Greek , "triangle", and , "head".
Cause
Trigonocephaly can either occur syndromatic or isolated. Trigonocephaly is associated with the following syndromes: Opitz syndrome, Muenke syndrome, Jacobsen syndrome, Baller–Gerold syndrome and Say–Meyer syndrome. The etiology of trigonocephaly is mostly unknown although there are three main theories. Trigonocephaly is probably a multifactorial congenital condition, but due to limited proof of these theories this cannot safely be concluded.
Intrinsic bone malformation
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 (9p22–24, 11q23, 22q11, FGFR1 mutation), metabolic (TSH suppletion in hypothyroidism) or pharmaceutical (valproate in epilepsy).
Fetal-head constraint
The second theory says that synostosis begins when the fetal head gets hindered in the pelvic outlet during birth.
Intrinsic brain malformation
The third theory predominates disturbed brain formation of the two frontal lobes as the main issue behind synostosis. Limited growth of the frontal lobes leads to an absence of stimuli for cranial growth, therefore causing premature fusion of the metopic suture.
Other conditions and syndromes
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
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 hypoplasia
Imaging 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 broadening
The 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.