In normal fetal development, the bony parts of the skull are connected by sutures, which are fibrous sheaths. These sutures do not normally begin to fuse, or become bony, until 6-7 months after birth. In craniosynostosis, the sutures prematurely fuse leading to an abnormal skull shape. As a result, there is reduced brain growth in the direction that is perpendicular to the fused bones. The brain, however, compensates by growing in the direction of the normal sutures and away from the prematurely fused sutures. In primary craniosynostosis, abnormal skull development is genetically determined. These newborns will have asymmetrical head shapes because the brain continues to grow at a normal rate, but solely in the direction of the unfused sutures. These children are often normal neurologically, tending to benefit from surgery to separate the prematurely fused bones. The opposite essentially occurs in secondary craniosynostosis. Most children are neurologically abnormal because of impaired brain growth. Rather than a genetic cause, a range of disorders and syndromes may cause impaired brain growth and the ensuing small head size. Craniosynostosis may occur without other findings (referred to isolated, representing 80-90% of cases) or be associated with multiple abnormalities, considered part of a genetic syndrome (10-20% of cases). More than 150 syndromes have been identified that include craniosynostosis as one of the findings.
The condition is present in 1 out of every 2,000 live births.
Craniosynostosis usually is not diagnosed by ultrasound until the third trimester. It should be suspected if the skull does not appear symmetric. For most of the conditions associated with craniosynostosis, long-bone growth is usually normal. It is particularly important to evaluate the fetal hands and feet, the central nervous system, and the heart. By ultrasound, the sutures normally are hypoechogenic, meaning they do not return the ultrasound signal and appear as dark areas on the images. In craniosynostosis, there is a loss of hypoechogenicity of the normal suture. If craniosynostosis is suspected, the sutures should be examined along their entire length. The skull sometimes begins to appear deformed several weeks before the sutures appear closed.
The most important consideration in the sonographic examination is the distinction between isolated and syndromic craniosynostosis. Ultrasound evaluation should also focus on signs for syndromes commonly seen in association with craniosynostosis. Fetuses at risk for Apert syndrome should be evaluated for abnormalities of the hands, eyes, heart, and brain. Pfeiffer syndrome is characterized by premature closure of the coronal sutures, underdevelopment of facial structures as well as broad thumbs and great toes. Pfeiffer syndrome, Type II is associated with a cloverleaf-shaped skull, face, finger and eye abnormalities, radially deviated digits, and occasional enlargement of a brain structure called the lateral ventricles.
Pregnancy Management Options and Outcomes
A detailed ultrasound and family history should be performed if craniosynostosis is suspected in addition to evaluation of each parent for syndromic features. Sometimes, an amniocentesis may be recommended to determine the underlying cause. An amniocentesis involves insertion of a needle into the uterine cavity, guided by ultrasound, then removal of some amniotic fluid. The amniotic fluid contains fetal cells that can be used for genetic testing. Most expectant mothers with suspected fetal craniosynostosis should still be offered an attempt at a vaginal delivery. This recommendation presumes other issues do not exist to suggest a cesarean section as the safer option.
Candidacy for Fetal Treatment
Craniosynostosis has not been successfully treated while the fetus is in utero. At this time, there are no procedures to correct or reverse the condition from progressing in utero.
Newborns are at risk for difficulties with breathing, feeding, and vision as well as increased pressure within the skull. The newborn will have a detailed physical examination. Additionally, a healthcare provider who specializes in recognizing and diagnosing genetic conditions will evaluate the newborn to assess for findings suggestive of a genetic syndrome. An x-ray may be performed to assess whether the sutures are completely or partially fused. Consultation with a neurosurgeon is indicated. Long-term outcomes and the risk for the condition to occur again in a future pregnancy depend on whether the condition is isolated are part of a greater genetic syndrome.
Surgery may need to be performed within the first year to allow appropriate brain growth and to allow for a possibly normal skull appearance. Surgery also reduces the pressure that might potentially develop in the brain. Sometimes, a single procedure is sufficient to correct the condition, mostly in cases of simple craniosynostosis. In more complicated cases, multiple procedures are often needed throughout childhood and into the teenage years.
Craniosynostosis is one of the most common human malformations. Eighty to ninety percent of cases are isolated, 10%–20% are syndromic. Differential diagnosis includes Muenke coronal craniosynostosis, Saethre–Chotzen syndrome, Apert syndrome, Crouzon syndrome, Pfeiffer syndrome, amongst other less common syndromes.