Craniosynostosis
Craniosynostosis is the pathologic condition that results from premature fusion of one or more sutures in the cranial vault, leading to a deformity of the vault and cranial base. The condition may be caused by a genetic disorder, be related to gestational toxic influences, or be a sporadic congenital finding.
When a suture fuses prematurely, the skull and the growing brain beneath the suture are restricted, leading to expansion into regions of the skull with less restriction. This “compensatory” growth of the skull occurs largely in planes parallel to the affected suture, resulting in consistent, recognizable cranial deformities.
The 6 fontanelles present at birth are the anterior, posterior, and paired anterolateral and posterolateral fontanelles. The posterior fontanelle closes first at about 2 months. The anterolateral fontanelles (corresponding to the pterion in the adult) normally close 3 months after birth. The posterolateral fontanelles (corresponding to the asterion in the adult) close at the end of the first year, and the anterior fontanelle, which is the last to close, generally does so by 2 years.
The median frontal, or metopic, suture usually closes by 2-6 years. In 10% of the population it remains open until adulthood, and the frontal sinuses are absent or hypoplastic. The remaining sutures close clinically at 6-12 months but do not ossify completely until after 30 years.
The neurocranium achieves 63% of its ultimate growth by birth, 88% by 1 year, and 95% by 10 years. The neonatal brain doubles in volume by 6 months and triples in volume by 2.5 years. By 16 years, the calvaria achieves its mature size and only changes slightly as the bone thickens and remodels over the following 3-4 years.
Primary and secondary causes
In most patients, craniosynostosis is a primary event and occurs sporadically. While the mechanism of primary craniosynostosis remains to be elucidated, there are many known secondary causes.
Craniosynostosis may be induced through internal and external forces. Prenatal compression of the fetal head is implicated as a cause of craniosynostosis. Internal forces known to cause craniosynostosis include a number of teratogens and diseases. Teratogens implicated in craniosynostosis include;
1. aminopterin,
2. diphenylhydantoin,
3. valproic acid,
4. oxymetazoline hydrochloride, and possibly
5. isotretinoin.
Craniosynostosis has been observed in association with a number of maternal metabolic disorders including
1. hyperthyroidism,
2. rickets,
3. Hurler syndrome,
4. Morquio syndrome,
5. beta-glucuronidase deficiency,
6. mucolipidosis III, and
7. a host of hematologic disorders.
Overall incidence of craniosynostoses is estimated at 1 in 2000-3000 births in the United States. The following terms describe premature fusion of the following sutures:
· One coronal suture - Plagiocephaly
· Both coronal sutures - Brachycephaly
· Metopic suture - Trigonocephaly
· Sagittal suture - Scaphocephaly
· Lambdoid suture - Occipital plagiocephaly
· Multiple cranial sutures - Acrocephaly, turricephaly, oxycephaly,
· Kleeblattschädel anomaly (all with different phenotypic appearances)
Syndromic dysostoses are associated with a variety of abnormal skull shapes. Although some syndromes typically occur with certain synostotic sutures, a wide range of combinations exists. Syndromic dysostoses are confounded by forces of growth in an abnormal facial skeleton. Varying relationships of syndrome and synostosis result.
Radiology
1. Plain skull radiographs were the first method used to radiologically evaluate patients with suspected craniosynostosis.
2. Closed sutures appear sclerosed or obliterated on CT bone windows; defects in parenchyma and ventricle spaces can be evaluated on soft tissue windows. Three-dimensional rendering of CT data provides a model of the cranial vault including a depiction of the patient's sutures and fontanelles, and accuracy is improving with newer generations of CT software. At most, obtain 1.5 -mm cuts to allow 3-dimension reconstructions of acceptable quality.
3. Sonograms have been used more recently to evaluate cranial sutures. Prenatal diagnosis may become common.
Current surgical treatment
Timing of surgery can vary depending on the type of craniosynostosis and its severity.
1. If pansynostosis is present, a surgical emergency exists since brain growth is not possible, and the operation may need to be repeated at intervals if reossification occurs, limiting cranial growth.
2. A child with significant scaphocephaly may be operated on at 3-4 months, but for most other conditions a better morphological result can be obtained by waiting until 6-8 months. The calvarial and orbital bone is better formed at this age and can be shaped and fixed with more precision and stability. The goals of surgery are to release the prematurely closed suture(s) and to reshape abnormally positioned bones so that they are in a proper position and symmetric with the contralateral side.
Treatment Plan
A genetic diagnosis and evaluation for other systemic condotions should be done at the time a prenatal diagnosis.
The newborn cleft baby should have
a pediatric evaluation,
parents are counseled about feeding and given infoormation.
Early treatment with presurgical orthopaedic and nasal molding is started at 2 weeks or earlier whenever possible.
After completion of the nasoalveolar molding, usually about 3 month, a surgical correction oof the cleft lip and nose is done.
