Abnormal ossification in infant skulls resulting in deformed or below average size skulls

1. Introduction

The common denominator for all children in this diagnostic group is that their skull sutures have fused too early - in fact even before birth, so that they were born with an abnormal skull shape.

2. What is craniosynostosis?

Literally, craniosynostosis means an ossification (turning into bone) of the sutures (the joints between the bones) of the skull. This means that one or more sutures between the skull bones closed too early. The skull consists of a number of bones that are connected to one another and able to move thanks to the sutures (see Illustration A and B).This enables the baby to go through the birth canal and allows the brain to grow without becoming wedged within the skull. The skull must grow at the same rate as the brain, but also as the eyes and the nasal sinuses.

As a rule, growth from the sutures is completed around 8 years of age. If a suture fuses too soon, this stops the growth. To compensate, growth will take place at those sutures that remain open. Depending on which of the sutures closes too soon, a typical skull shape will develop.

Craniosynostosis

All abnormal skull shapes have their own names.

There are eight skull shapes, classified as follows:

  • Triangle-shaped skull - Trigonocephaly
  • Short skull - Brachycephaly
  • Oblique skull - Plagiocephaly
  • Posterior head deformity - Occipital Plagiocephaly
  • Boat-shaped skull - Scaphocephaly
  • Trapezoidal head with abnormal skull thickness - Pachycephaly
  • Tower or cone skull - Oxycephaly
  • Cloverleaf skull or Kleeblattsch├Ądel - Triphyllocephaly

The skull shapes described above frequently occur without any other physical abnormalities. This is referred to as "isolated craniosynostosis". It occurs in approximately 1 in every 1600 births. If there are other physical anomalies, e.g. of the face, the hands or the feet, a more complex clinical picture is involved, which is called craniosynostosis syndrome or craniodysostosis.

3. How does craniosynostosis come about?

The fusing or ossification of the skull sutures is a normal process. Different sutures fuse at different times. The metopic suture of the forehead closes in the first year of life. The coronal suture can close from age 8 onwards. The cause of premature fusion is not known. What is known is that craniosynostosis syndromes involve a hereditary factor related to a chromosome or a gene. The sutures may also close prematurely as a result of a lack of development of the brain. In these cases, the skull does not need to grow further. This also applies to the drop in intracranial pressure that can occur in the treatment of hydrocephalus with the aid of a shunt pump. These cases are described as "secondary craniosynostosis". Both paediatricians and geneticists can contribute to finding the cause for the craniosynostosis

4. What are the consequences?

The consequences vary widely depending on the type of craniosynostosis. In isolated craniosynostosis, there need be no further problems aside from the abnormal skull shape. Sometimes, however, a certain degree of mental development deficiency can occur. Increased intracranial pressure can also occur in varying percentages. Craniosynostosis syndromes frequently have distinct consequences. In addition to impaired growth of the facial structures, often including an underdeveloped upper jaw, the brain, eyes, ears and airways can also be functionally impaired. This is discussed under the individual condition descriptions.

5. What can be done?

In view of the fact that a prematurely fused suture is abnormal and leads to a malformation of the remainder of the skull, a logical step is to open it up again. In practice, however, just opening the suture does not provide sufficient improvement. The existing anomalies do not spontaneously return to normal. More extensive corrections are required. In younger patients a reconstruction of the calvaria, possibly combined with a partial eye socket correction, is enough as a rule. This operation is usually performed in the first year of life. In simple, isolated craniosynostoses this is usually sufficient. Craniosynostosis syndromes will also require facial corrective surgery in later years, due to the diminished growth of the upper jaw in particular. This becomes more obvious in puberty. The most suitable surgery options are indicated in conjunction with the description of the different types of craniosynostoses.