Friday 2 November 2012

Metopic Synostosis

'Trigonocephaly' Metopic Synostosis

Note the associated excessive convolutional marking on inner table of skull with dilated parietal emissary foramen indicating long term raised intra cranial pressure.

Craniosynostosis (from cranio, cranium; + syn, together; + ostosis relating to bone) is a condition in which one or more of the fibroussutures in an infant skull prematurely fuses by ossification.  thereby changing the growth pattern of the skull. Because the skull cannot expand perpendicular to the fused suture, it compensates by growing more in the direction parallel to the closed sutures. Sometimes the resulting growth pattern provides the necessary space for the growing brain, but results in an abnormal head shape and abnormal facial features. In cases in which the compensation does not effectively provide enough space for the growing brain, craniosynostosis results in increased intracranial pressure leading possibly to visual impairment, sleeping impairment, eating difficulties, or an impairment of mental development combined with a significant reduction in IQ.

Craniosynostosis occurs in one in 2000 births. Craniosynostosis is part of a syndrome in 15 to 40% of the patients, but it usually occurs as an isolated condition.

Causes of premature fusion
The dura mater plays an important role in determining closure or patency of the suture.
Many things are still not understood about the suture biology and the exact causative pathways remain yet to be completely understood.
Multiple potential causes of premature suture closure have been identified, such as the several genetic mutations that are associated with syndromic craniosynostosis.The cause of nonsyndromic craniosynostosis however, is still greatly unknown. Most likely, a role is played by biomechanical factors, as well as environmental, hormonal and genetical factors.
Biomechanical factors: fetal head constraint during pregnancy.
Environmental factors : maternal smoking and the maternal exposure to amine-containing drugs likely through effects on fibroblast growth factor receptor genes.
Hormonal factors: Hyperthyroid induced craniosynostosis is a hormone mediated premature closure due to high levels of thyroid hormone.
Genetic factors : fibroblast growth factor receptor 3 (FGFR3) and TWIST genes.

The name providing a direct hint regarding the deformity of the skull. The literal meaning of the Greek derived word ‘scaphocephaly’ is boathead. A synonymous term is 'dolichocephaly' (the prefix dolicho- means elongated).
Premature sagittal suture closure restricts growth in a perpendicular plane, thus the head will not grow sideways and remain narrow.
This is best seen in a view standing above the child looking downwards at the top of the head.
A prominent forehead, called frontal bossing, and a prominent back portion of the head, called coning. When viewed from sideways the resulting shape of the head will look a bit like a boat.

A result from the premature closure of the metopic suture result in a narrow forehead, which is even further emphasized by ridging of the suture. The resulting shape can best be assessed from a top view again, which will reveal a somewhat triangular form of the head.
Trigonocephaly is also a Greek derived word, which can be translated as triangular shaped head. A facial feature of metopic synostosis is hypotelorism.

The Greek word plagios means skew. Plagiocephaly can be sub classified in Anterior Plagiocephaly and Posterior Plagiocephaly.
Anterior Plagiocephaly
Anterior plagiocephaly is a clinical description of unilateral coronal synostosis. Children born with unilateral coronal synostosis develop due to compensatory mechanisms a skew head; a plagiocephaly.
The sagittal suture ‘divides’ the coronal suture in two halves; unilateral meaning that either the right side or the left side to the sagittal suture is fused. This fact immediately raises an important point. Unlike closure of the sagittal or the metopic suture, right and left are not the same in unilateral coronal synostosis. This asymmetry shows in the skull deformity, as well as in the facial deformity and the complications.
This time, the skull deformity can only partly be predicted using Virchow’s law. Growth is arrested in the plane perpendicular to the fused suture and the forehead is flattened, but only at the ipsilateral side of the head. Ipsilateral indicates the same side of the head as where the suture is closed. Compensatory growth occurs in a parallel plane, as well as in a perpendicular plane. An increase in growth at the metopic and the sagittal suture accounts for the parallel plane and will result in bulging at the temporal fossa and an increase in width of the skull. Compensatory growth in the perpendicular plane occurs on the side of the head with the patent coronal suture, the contralateral side. Half of the forehead will bulge forwards as a result.
Assessment of the skull from a top view shows asymmetry of the frontal bones, an increased width of the skull and a forward displacement of the ear at the ipsilateral side of the head.Assessment of the skull from a frontal view will show asymmetrical features of the face, including a displacement of the chin point of the jaw and a deviation of the tip of the nose.The chin point is located more to the contralateral side of the head, due to the ipsilateral forward displacement of the temporomandibular joint together with the ear.The tip of the nose will also point towards the contralateral side.Complications based on the skull deformation include malocclusion of the jaw and in as many as 90% - a subtle form of - strabismus, the last being caused by the asymmetrical placement of the orbits.
Posterior Plagiocephaly
Unilateral lambdoid synostosis is also called posterior plagiocephaly, indicating that this gives, just like unilateral coronal synostosis, a ‘skew head’. The difference is that this time, the deformity mostly shows at the occiput.
Restriction of growth will occur at the ipsilateral side of the head; compensatory growth will occur at the contralateral side of the head. This growth pattern exerts an effect at the base of the skull, which is not even when the child is assessed from a point of view standing behind the child, as well as on the cervical spine, which shows a curvature. In addition, an asymmetry of the ears can be seen, with the ear on the ipsilateral side placed further to the back. Also, again from a point of view standing behind the child, a bulging of the mastoid can be seen. Minimal forehead asymmetries are typically seen.

Brachycephaly, or a ‘short head’, is the result of a closure of both the coronal sutures result in a child’s head with a restriction of growth in the forward direction and in the backward direction; recessed frontal bones and a flattened occiput. compensatory growth will occur sideways, due to the sagittal suture, and upwards, due to the lambdoid sutures.

Oxycephaly, also known as turricephaly and high-head syndrome, is a type of cephalic disorder. This is a term sometimes used to describe the premature closure of the coronal suture plus any other suture, like the lambdoid,

The word pansynostosis is also Greek derived and can be translated as ‘all one bone’, indicating that all of the sutures are closed. The term is used to describe the children with three or more sutures closed. Pansynostosis can present in several ways. The appearance can be the same as that seen with primary microcephaly: a markedly small head, but with normal proportions.

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