Craniosynostosis is the premature closure of a cranial suture. Isolated craniosynostosis (nonsyndromic craniosynostosis) occurs in about one in 2,500 births. The metopic suture is the only cranial suture that normally closes before adulthood. The metopic suture usually closes at about 6-9 months of age. All of the other cranial sutures should remain open until adulthood, long after the brain has stopped growing.
A baby’s skull has 6 major cranial sutures:
• The metopic suture
• Two coronal sutures
• The sagittal suture
Any of these sutures may close earlier than normal. An infant's brain is growing very quickly, more than tripling in size in the first two years of life. The growing brain “stretches” the cranial sutures which stimulates the skull bones to grow and make room in the skull for the growing brain. This system allows the skull to remain just large enough for the brain it protects.
In craniosynostosis a cranial suture closes earlier than it should which restricts growth of the skull bones in the area of the suture. This is a problem because the brain continues to grow at the same pace so the remaining open sutures must make up the difference and grow more bone to create enough space for the growing brain. Closure of each of the major sutures causes a recognizable pattern of growth and abnormal head shape. The position of the closed and remaining open sutures determines how the skull will grow and what the shape will be.
The two biggest concerns related to craniosynostosis are the risk of elevated pressure inside the skull and the emotional and psychosocial effects of skull deformity. As stated above, even when the sutures close prematurely, the brain continues to grow at the same rate. Therefore, the remaining open sutures must grow faster to create enough space inside the skull for the growing brain. In about 15 out of 100 patients with one prematurely closed cranial suture (single suture craniosynostosis) the skull does not grow fast enough to keep up with the rapid growth of the brain.This results in an increased pressure inside the skull that can be harmful to the health of the brain. This is called elevated intracranial pressure (ICP). The more closed sutures there are, the higher the likelihood that the skull will not be able to grow fast enough. When two sutures are closed the risk of elevated intracranial pressure is over 40%. Very high pressure in the skull can cause learning delays and blindness.
When craniosynostosis affects any of the cranial sutures increased growth occurs in the remaining open sutures (compensatory growth) that results in an abnormal head shape. The abnormal head shape is characteristic and predictable for each closed suture. The common forms are listed below:
- Sagittal Synostosis (Scaphocephaly)
- Metopic Synostosis (Trigonocephaly)
- Coronal Synostosis (Unicoronal or Bicoronal)
- Lambdoidal Synostosis