Trigonocephaly

Trigonocephaly is a congenital condition due to premature fusion of the metopic suture (from Ancient Greek metopon 'forehead'), leading to a triangular forehead. The premature merging of the two frontal bones leads to transverse growth restriction and parallel growth expansion. It may occur as one component of a syndrome together with other abnormalities, or in isolated form. The term is from Ancient Greek trigonon 'triangle' and kephale 'head'.

Trigonocephaly can either occur in a syndrome or isolated, all by itself. Trigonocephaly is associated with the following syndromes: Bohring-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.

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).

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

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.^{[citation needed]}

Other conditions and syndromes with trigonocephaly include:

Diagnosis can be characterized by typical facial and cranial deformities.

Observatory signs of trigonocephaly are: