Trigonocephaly

A congenital anomaly in the form of a deformity of the skull, in which the head of babies has an irregular shape, and the skull looks triangular, is defined as trigonocephaly (from the Greek trigonon - triangle and kephale - head). [1]

Epidemiology

The prevalence of craniosynostosis is estimated at about five cases per 10 thousand live births (or one case per 2–2.5 thousand people in the general population). [2]

In 85% of cases, craniosynostosis is sporadic, the remaining cases occur as part of the syndrome. [3]

According to statistics, premature fusion of the median frontal suture is the second most common form of craniosynostosis, and trigonocephaly accounts for one case per 5-15 thousand newborns; the number of male infants with this anomaly is almost three times higher than newborn girls. [4]

In about 5% of cases, this congenital anomaly is present in the family history. [5]

Causes of the trigonocephaly

The normal formation of the skull occurs due to the presence in it of centers of primary growth and bone remodeling - craniofacial synarthroses (joints), which, in the process  of development of the head skeleton  , close at a certain time, providing bone fusion. [6]

The frontal bone (os frontale)  of the skull of a newborn  consists of two halves, between which there is a vertical fibrous connection - the median frontal or metopic suture (from the Greek metopon - forehead), running from the top of the back of the nose up the midline of the forehead to the anterior fontanel. This is the only fibrous cranial suture that heals during infancy: from 3-4 months to 8-18. [7]

See also -  Changes in the skull after birth

The causes of trigonocephaly are metopic  craniosynostosis  (craniostenosis) or metopic synostosis (from the Greek syn - together and osteon - bone), that is, premature (up to the third month) immobile fusion of the bones of the cranial vault together along the median frontal suture. Thus, craniosynostosis and trigonocephaly are related as cause and effect, or as a pathological process and its result. [8]

In most cases, trigonocephaly in a child is the result of primary (isolated) craniosynostosis, the exact cause of which is unknown. Isolated craniosynostosis occurs sporadically, probably due to exposure to a combination of genetic and environmental factors. [9]

But trigonocephaly can be part of congenital syndromes resulting from chromosomal abnormalities and mutations in various genes. These include: Opitz trigonocephaly syndrome (Bohring-Opitz syndrome),  Apert syndrome, Lois-Dietz syndrome, Pfeiffer syndrome, Jackson-Weiss syndrome, craniofacial dysostosis or  Crouzon syndrome , Jacobsen, Setre-Chotzen, Müncke syndromes. In such cases, trigonocephaly is called syndromic. [10]

At birth, the brain is typically 25% of its adult size, reaching about 75% of an adult's brain by the end of the first year of life. But with the primary growth retardation of the brain, the so-called secondary craniosynostosis is possible. The etiology of the delay is associated with metabolic disorders, some hematological diseases, teratogenic effects on the fetus of chemicals (including those contained in pharmaceuticals). [11]

According to experts, trigonocephaly in adults who were not treated in childhood, as a result of isolated craniosynostosis or a congenital syndrome, persists throughout life. [12]

Risk factors

Experts consider genetic factors to be the main risk factors for trigonocephaly (and metopic craniosynostosis as its cause): over the past two decades, more than 60 genes have been identified whose mutations are associated with premature immobile fusion of cranial bones in infants.

There is an increased risk of developing pathologies of craniofacial synarthrosis and general osteogenesis (bone formation) in cases of improper presentation of the fetus, its intrauterine hypoxia, multiple pregnancies, drinking alcohol, drugs or smoking during childbearing. [13]

Pathogenesis

According to the prevailing theory, the pathogenesis of trigonocephaly lies in the violation of fetal osteogenesis in early pregnancy, most often due to genetic factors, since random chromosomal abnormalities are detected in newborns with metopic craniosynostosis. For example, one of the most common is trisomy 9p, leading to craniofacial and skeletal defects, mental retardation and psychomotor development. [14]

Due to too early fusion of the median frontal suture, growth in this region of the skull is difficult: the lateral growth of the frontal bone is limited with shortening of the anterior cranial fossa; a bone ridge is formed along the midline of the forehead; there is a convergence of the bones that form the eye orbits, and an impression of the temporal bones. [15]

But the growth of the skull in other areas continues: there is a compensatory sagittal (anteroposterior) and transverse growth of the back of the skull (with the expansion of its parietal-occipital part), as well as vertical and sagittal growth of the upper face. As a result of these violations, the skull acquires an irregular shape - triangular. 

Symptoms of the trigonocephaly

The main symptoms of trigonocephaly are a change in the shape and appearance of the head:

• when viewed from above at the top of the head, the skull has the shape of a triangle;
• narrowed forehead;
• a noticeable or palpable ridge (bone protrusion) running along the center of the forehead, giving the frontal bone a pointed (keeled) shape;
• deformation of the upper part of the orbits (flattening of the supraorbital ridges) and hypotelorism (reduced distance between the eyes).

The frontal (anterior) fontanel may also be prematurely closed.

In syndromic trigonocephaly, there are other anomalies and signs  of mental retardation in children . [16]

Complications and consequences

In severe cases, this congenital anomaly is accompanied by increased intracranial pressure, causing vomiting, headaches, and decreased appetite. [17]

In addition, increased intracranial pressure provokes severe brain damage, which can lead to cognitive impairment or developmental delay. [18]

Diagnostics of the trigonocephaly

Trigonocephaly is diagnosed at birth or within a few months shortly after the baby is born. However, less pronounced findings of metopic craniosynostosis may remain undetected until early childhood.

To visualize the pathology of the skull, instrumental diagnostics are performed using computed tomography of the head, ultrasound.  [19], [20]

Differential diagnosis

Differential diagnosis is necessary to distinguish a syndromic defect from an isolated metopic synostosis, for which the child is given  a genotype analysis .

Treatment of the trigonocephaly

In some children, cases of metopic synostosis are mild enough (when there is only a noticeable furrow on the forehead and no other symptoms) that do not require specific treatment. [21]

The treatment of severe trigonocephaly is surgical, and consists in an operation to correct the shape of the head and ensure normal brain growth, as well as surgical correction of facial bone deformities. [22]

Such surgery - synostectomy of the metopic suture, displacement of the orbital margin and cranioplasty - is performed at the age of up to 6 months. Until the age of one year, the child is under observation; during the first years of a child's life, they are periodically examined to make sure there are no problems with speech, motor skills, or behavior. [23]

Prevention

Methods for the prevention of this birth defect have not been developed, but genetic counseling can prevent the birth of a child with an incurable craniocerebral pathology.

And it is possible to identify craniosynostosis in a fetus during a prenatal ultrasound of its head in the second and third trimesters of pregnancy.

Forecast

In many ways, the prognosis depends on the degree of skull deformation, which affects the neurocognitive functions of the brain. And unless corrective surgery has been performed, children with trigonocephaly—compared to healthy peers—have lower overall cognition, speech, vision, attention, and behavior problems.