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Synostosis / Craniosynostosis

Definition :
Craniosynostosis is a birth defect in which one or more of the fibrous joints between the bones of an infant's skull close prematurely, before the infant's brain is fully formed. As a result of craniosynostosis, your baby's brain can't grow in its natural shape and his or her head is misshapen.

Craniosynostosis can affect one or more of the joints in an infant's skull. In some cases, craniosynostosis may be associated with an underlying brain abnormality that prevents the brain from growing properly.

Treating craniosynostosis usually requires that your infant undergo surgery to separate the fused bones. If there's no underlying brain abnormality, the surgery allows the brain adequate space to grow and develop.

Causes :
The cause of craniosynostosis is unknown. However, there's a hereditary component to craniosynostosis when it occurs with certain genetic syndromes, such as Apert's syndrome and Crouzon syndrome. Besides misshapen heads, infants with these syndromes often have seizures, blindness, developmental delays and mental retardation.

When to seek medical advice :
Contact your doctor if you think your baby's head isn't growing as it should or if it has an unusual shape.

Symptoms :
Your infant's skull comprises seven bones. Normally, the bones don't fuse until around the age of 2, giving your baby's brain time to grow. Joints called cranial sutures, made of strong, fibrous tissue, hold the bones together. In the front of your baby's skull, the sutures intersect in the large soft spot (fontanel) on the top of your baby's head. Normally, the sutures remain flexible until the bones fuse.

There are two categories of craniosynostosis, primary and secondary :

  • Primary craniosynostosis. If your baby has primary craniosynostosis, usually one but sometimes more of the cranial sutures become rigid, fusing the connecting bones and inhibiting the brain's ability to grow normally.
  • Secondary craniosynostosis. With secondary craniosynostosis, which occurs more frequently than the primary type, the infant's brain stops growing, usually due to an underlying hereditary syndrome, allowing the sutures to fuse prematurely. Secondary craniosynostosis is often associated with facial deformities and developmental delays.

The main sign of craniosynostosis is a misshapen skull. The shape depends on which of the cranial sutures are affected. The most common types of craniosynostosis are :

  • Sagittal synostosis (scaphocephaly). Premature fusion of the suture at the top of the head (sagittal suture) forces the head to grow long and narrow, rather than wide. The most common type of craniosynostosis, scaphocephaly is more common in boys.
  • Coronal synostosis (anterior plagiocephaly). Premature fusion of one of the sutures that run from each ear to the sagittal suture on top of the head may force the baby's forehead to flatten on the affected side. It also may raise the eye socket and cause a deviated nose and slanted skull. This second most common type of craniosynostosis is more common in girls. Untreated, it may lead to vision loss on the affected side (amblyopia).
  • Bicoronal synostosis (brachycephaly). When both of the coronal sutures fuse prematurely, the baby may have a flat, elevated forehead and brow.

Two rarer types of synostosis are :

  • Metopic synostosis (trigonocephaly). The premature fusion metopic suture runs from the baby's nose to the sagittal suture. It gives the scalp a triangular appearance.
  • Lambdoid synostosis (posterior plagiocephaly). This rarest form of craniosynostosis involves the lambdoid suture, which runs across the skull near the back of the head. It may cause flattening of the head on the affected side.

Besides unusual head shape, signs of craniosynostosis include :

  • Abnormal feeling "soft spot" (fontanel) on your baby's skull
  • Early disappearance of the fontanel
  • Slow or no growth of head as baby grows
  • Development of a raised, hard ridge along affected sutures
  • Increased intracranial pressure

The signs of craniosynostosis may not be noticeable at birth, but they will become apparent with the first few months of your baby's life.

On the other hand, a misshapen head doesn't always indicate craniosynostosis. For example, if the back of your baby's head appears flattened, it could be the result of your baby's sleeping on his or her back. The "Back to Sleep" campaign, co-sponsored by the National Institute of Child Health & Human Development, encourages parents to put healthy babies to sleep on their backs to reduce the risk of sudden infant death syndrome (SIDS). The campaign has resulted in more cases of misshapen heads. In this case, the flattening is a result of positional molding, not synostosis.

Dignosis :
Your doctor will feel your baby's head for abnormalities, such as suture ridges, perform a physical exam and look for facial deformities. In addition, your doctor may order other tests, including :

  • Imaging studies. X-rays or a computerized tomography (CT) scan of your baby's skull will show whether any sutures have fused. Fused sutures are identifiable by their absence because they're invisible once fused and by the ridging of the suture line.
  • Genetic testing. If your doctor suspects your baby's misshapen skull is caused by an underlying hereditary syndrome, genetic testing may help identify the syndrome. Genetic tests usually require a blood sample. Depending on what type of abnormality your doctor is looking for, your baby may be required to give a hair, skin or other tissue sample, such as cells from the inside of the cheek. Your sample is then sent to a lab for analysis.

Complications :
Babies with craniosynostosis, particularly those with an underlying syndrome, may develop increased intracranial pressure. Their skulls don't expand enough to make room for their growing brain. If untreated, increased intracranial pressure can cause blindness and brain damage. Rarely, it may be fatal.

In addition, facial deformities that affect the middle of the face may cause upper airway obstructions, compromising your baby's ability to breathe. Untreated, craniosynostosis may result in permanent head deformity.

Mild cases of craniosynostosis — those that involve only one suture and no underlying syndrome — may require no treatment. Skull abnormalities may become less obvious as your infant grows and develops hair.

For other infants, surgery, usually during infancy, is the primary treatment for craniosynostosis. However, the type and timing of surgery depend on the type of synostosis and whether there's an underlying syndrome.

The purpose of surgery is to relieve pressure on the brain, create room for the brain to grow normally and improve your child's appearance. A team that includes a specialist in surgery of the head and face (craniofacial surgeon), and a specialist in brain surgery (neurosurgeon) often performs the surgery.

  • Traditional surgery. The surgeon makes an incision in your infant's scalp and reshapes the affected portion of the skull. Sometimes, plates and screws, often made of material that absorbs over time, are used to hold the bones in place. Surgery, which is performed under general anesthesia, may take up to seven hours.

    After surgery, your infant remains in the hospital for at least three days. Some temporary facial swelling is common after surgery. Complications are rare. Some children may require a second surgery later on because the synostosis recurs. Also, children with facial deformities often require future surgeries to reshape their faces.

  • Endoscopic surgery. This less invasive form of surgery isn't an option for everyone. But in certain cases, the surgeon may use a lighted tube (endoscope) inserted through one or two small scalp incisions over the affected suture. The surgeon then opens the suture to enable your baby's brain to grow normally. Endoscopic surgery usually takes about an hour, causes less swelling and blood loss, and shortens the hospital stay, often to one day after surgery.

If your baby has an underlying syndrome, your doctor may recommend regular follow-up visits after surgery to monitor head growth and check for increased intracranial pressure.

Please be aware that this information is provided to supplement the care provided by your physician. It is neither intended nor implied to be a substitute for professional medical advice. CALL YOUR HEALTHCARE PROVIDER IMMEDIATELY IF YOU THINK YOU MAY HAVE A MEDICAL EMERGENCY. Always seek the advice of your physician or other qualified health provider prior to starting any new treatment or with any questions you may have regarding a medical condition.
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