Craniosynostosis is a condition of the premature fusion of one or more cranial sutures, which results in characteristic skull shape deformities and facial asymmetry accompanied by functional consequences such as increased intracranial pressure (ICP), visual impairment, deafness and cognitive deficits411121418). Craniosynostosis can occur primarily and secondarily. Premature fusion of one or more of the sutures is believed to be due to a developmental error during embryogenesis in primary craniosynostosis whereas secondary craniosynostosis is due to mechanical causes such as intrauterine compression of the fetal skull, metabolic causes, and the effect of teratogens. Approximately 85% of primary craniosynostosis cases occur as an isolated condition and the remaining 15% are a part of a multisystem syndrome1013).

Imaging is essential for the accurate diagnosis, surgical planning, post-treatment evaluation and identification of coexisting anomalies and complications associated with craniosynostosis. Because of its superior bone depiction, computed tomography (CT) with three-dimensional (3-D) reconstruction is the primary imaging technique used in craniosynostosis. However, exposure to ionized radiation from CT scans, especially in infants, has led researchers to explore alternative imaging techniques and protocols for craniosynostosis including the use of ultrasonography, plain skull radiography and magnetic resonance imaging (MRI). Here we present imaging findings in patients with normal craniums, craniosynostosis and its mimics and discuss the optimal imaging technique for the diagnosis, treatment planning and follow-up of craniosynostosis.

Although 3-D CT has superior diagnostic value, concerns about the hazards of radiation exposure in children has led to a consensus to avoid or postpone radiographic CT imaging until the end of the first year of life or as late as possible in children with suspected or diagnosed craniosynostosis1151617). The first step in assessing patients with an abnormal skull shape is a clinical examination in which almost all forms of monosutural craniosynostoses can be diagnosed. If there is a question of the diagnosis, ultrasonography is the technique of choice for diagnosis of neonates and infants. This simple and radiation-free technique can differentiate fused or patent sutures effectively and differentiate nonsynostotic pathology, such as positional skull deformities and molding, from craniosynostosis2021). Increase of the width of the cranial sutures on serial sonograms may provide evidence for a possible increase in ICP, which is a major complication of craniosynostosis20). Schweitzer et al.17) investigated the individual features of all forms of craniosynostosis in plain skull radiography (AP and lateral images) to achieve proper diagnosis while avoiding the use of a CT scan. The effective radiation dose of plain skull radiography is approximately 0.01 mSv to 0.04 mSv. In monosutural craniosynostosis, plain skull radiography is only indicated in children with remaining diagnostic doubts after clinical and sonographic evaluation, immediately prior to surgery or in non-surgical cases after the first year of life to access for additionally affected sutures16). A CT scan may be unavoidable in complex (multisutural and syndromic types) or complicated types of craniosynostosis for treatment planning. The reported effective dose of radiation for a 3-D CT scan is in the range of 0.2 mSV to 2 mSV35822). Recently, Ernst et al.7) reported that a 0.08 mSv 3-D CT protocol by using Model Based Iterative Reconstruction can be used in children with cranial deformities without compromising imaging quality. In a phantom study, Kaasalainen et al.9) achieved sufficient image quality using a CT protocol with an effective radiation dose of 0.02 mSv, which is comparable to the effective dose of plain skull radiography. Although this ultra-low-dose CT technique is not widely available presently and the diagnostic value for minor sutures is still questionable, these results are promising in children with complex craniofacial malformations who undergo repeated CT scans at the time of diagnosis and at various stages of surgical correction. The role of MRI in craniosynostosis has been limited due to its unreliability in identifying the cranial sutures. However, with advantages of radiation-free and excellent soft-tissue contrast, MRI has been an important modality in combination with ultrasonography in infants with suspected associated intracranial anomalies and complications of craniosynostosis. As mentioned above, Eley et al.6) established a novel 3-D MRI technique ("Black Bone") that is able to individually identify the cranial sutures similar to other 2-D imaging modalities. Further research is necessary to standardize the use of 3-D MRI's of the cranium; however, this technique is revolutionary for radiosensitive infants with craniosynostosis.

With advancements in devices and technology, we can presently apply MRI and 0.2 mSv 3-D CT to inspect the cranial bones, sutures and soft tissue of children with craniosynostosis. However, clinical evaluation followed by ultrasonography should be considered the first step for imaging diagnosis in infants with craniosynostosis. MRI should be considered in children with suspected intracranial anomalies and complications. Plain skull radiography satisfies the clinical need in the majority cases involving monosutural craniosynostosis, even for preoperative planning of surgical correction and postoperative follow-up. CT should be reserved for children with complex craniofacial deformities to plan the management of the disease. Presently, available commercial low-dose 3-D CT scanners have an effective radiation dose of approximately 0.2 mSv. In addition, 3-D MRI and ultra-low-dose 3-D CT scanners are expected as an alternative to plain skull radiography in the near future.