Although brain growth is not complete until about 20 years of age, two-thirds of it occurs in the first 2 years of life. Following birth, the cranial sutures maintain separation of the calvarial bones as the skull accommodates the growing brain. The expanding brain also stimulates new bone deposits at the contact edges of the sutures. If one or more of the sutures are fused at birth, the skull will expand into the abnormal head shapes and facial distortions that characterize craniosynostosis.
In simple craniosynostosis, a single suture is fused. Complex or syndromic craniosynostosis involves the fusion of multiple sutures. More than 180 inherited syndromes, such as Crouzon, Pfeiffer, and Apert syndromes, manifest craniosynostosis. Some of these syndromes are associated with developmental delays, a restricted airway, and protruding eyes.
Abnormal head shape in infants also can be caused by positional plagiocephaly, a much more common and benign condition that can be addressed through nonsurgical intervention with the aid of physical and occupational therapy. Treatment may involve:
The incidence of craniosynostosis is 1 in 2,500 live births. Of those cases, only 6% are complex or syndromic.
Fusion of the sagittal suture is the most common form of simple craniosynostosis, accounting for 40% to 60% of cases. It occurs predominantly in males and is characterized by an elongated skull, bitemporal narrowing, and frontal and occipital bossing.
The flat, asymmetrical head shape in positional plagiocephaly is sometimes confused with posterior unilateral lambdoid synostosis, a subtype of craniosynostosis.
Craniosynostosis management at Mayo Clinic is conducted by an interdisciplinary team whose members vary depending on the type of craniosynostosis involved. All patients with craniosynostosis are seen by specialists in neurosurgery, plastic surgery, and medical genetics. To care for patients with syndromic craniosynostosis, the team may also include specialists in:
Nicholas M. Wetjen, M.D., a pediatric neurosurgeon at Mayo Clinic, notes that although there is no upper age limit for a referral, the optimal time is between 1 and 2 months of age. The diagnosis is based on a physical examination and imaging studies. The goal is to differentiate normal from abnormal growth patterns and positional plagiocephaly from craniosynostosis and to identify craniosynostosis subtype. Dr. Wetjen says that he prefers to meet and get to know a patient's family, even if it is just to offer reassurance, to monitor the child, or to help the family avoid an unnecessary procedure.
Dr. Wetjen and his colleagues have determined that when surgery is required, the optimal age is between 4 and 6 months, although surgical reshaping can be done at any age. In all cases of craniosynostosis, the bones have a tendency to grow together again, but simple craniosynostosis rarely requires a second procedure.
Dr. Wetjen notes: "Our patients with simple craniosynostosis tend to do very well. We usually do a single operation and see them for follow-up a few times in the first year and again after 5 years. We rarely have to operate again. Those with syndromic or complex craniosynostosis may require more than one procedure and are actively monitored for a wide range of potential problems by our comprehensive management team."
During surgery, a pediatric neurosurgeon removes bone at the suture site, and a plastic surgeon conducts the reconstruction and remodeling of the head. In some cases, surgery may be performed endoscopically. According to Dr. Wetjen, the endoscopic outcomes are similar to the standard surgical procedure, but endoscopy requires that the patient wear a helmet for approximately 1 year after surgery.
What causes cranial sutures to fuse before birth? Dr. Wetjen and Jennifer Jane Westendorf, Ph.D., a scientist in orthopedic surgery and biochemistry and molecular biology at Mayo Clinic, have been collaborating over the past year to understand more about the mechanism of premature bone fusion.
It is thought that bone at the cranial sutures grows in response to signals from the dura mater and that in craniosynostosis, gene mutations alter the signal or signaling process. In 15% of craniosynostosis cases, the genetic mutation is known. Dr. Westendorf and colleagues are in the process of developing a genome-wide approach to identify other gene mutations.
Dr. Westendorf explains that determining the molecular basis of premature bone fusion will provide insights into craniosynostosis and bone formation in general. This knowledge could impact other skeletal diseases and disorders, such as osteoporosis and fracture repair.
Dr. Wetjen adds that their research may also contribute to the design of structural scaffolding to improve reshaping of the head in craniosynostosis. Their research utilizes what would have been waste tissue—the bone that is removed during surgery for craniosynostosis.
Drs. Westendorf and Wetjen are pleased to note that all of the families coming to Mayo for craniosynostosis surgery over the course of the project have been eager to participate in it.