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Background
Craniosynostosis (CS) is characterized by the early fusion of one or more sutures in the skull. It occurs in about 4–6 infants per 10, 000 live births. The resultant fusion leads to distinctive abnormalities in the shape of the skull and the face. CS may be associated with increased intracranial pressure, compromised vision, hearing loss, and difficulties in cognitive functions. We present a review and update of the different imaging modalities used when diagnosing CS.

Educational Goals / Teaching Points
Review conventional imaging for the evaluation of CS with the 3D CT as gold standard. Comment on other emerging tools used for evaluation. Black Bone (BB) MRI is emerging as a new useful tool for the diagnosis of CS. Ultrasonography (US) is lower cost and works as a screening tool without radiation.

Key Anatomic/Physiologic Issues and Imaging Findings/Techniques
An intact patent suture is depicted as a radiolucent line with serrated and nonlinear characteristics on both standard skull radiographs and 3D images. A suture that has fused prematurely exhibits perisutural sclerosis, a linear appearance, diminished serration, the presence of bony bridging, or even the absence of the suture, as discernible on a radiograph or CT scan. Plain x-rays are also low cost but have the lowest accuracy rate out of other radiographic options. Still, they are regarded as a reliable general screening diagnostic tool. Schweitzer and colleagues listed typical radiological characters of CS and diagnosed 127 cases with plain x-ray that were later confirmed by intraoperative findings. Three-dimensional CT is the gold standard imaging tool, but due to the risk of ionizing radiation in neonatal/pediatric population, it is important to consider alternative imaging modalities. US reveals a standard patent suture as a continuous hypoechoic fibrous gap situated between cranial bones with higher echogenicity; on a transverse scan of the sagittal sinus, it appears end-to-end, and on transverse scans of the coronal and lambdoid sutures, it presents a beveled configuration. Additional US observations delineating CS encompass an unevenly thickened inner suture border, absence of a beveled contour, and asymmetric fontanels. Cranial US can reliably diagnose patients with partial and total fusions based on the ultrastructural details of bony and soft tissue adjacent to synoptic suture(s). Standard MRI is not decisive in revealing sutures. Nevertheless, Eley et al. introduced a new gradient echo parameter termed low flip angle gradient echo MRI sequence, also known as BB MRI. BB MRI enables the creation of 3D reconstructions of the craniofacial skeleton, enhancing the visualization of cranial sutures. Although the use of ultrashort echo time sequences such as that employed in the low flip angle gradient echo MRI sequence are encouraging, it cannot be done using the typical MRI hospital scanner.

Conclusion
Each modality has its advantages and disadvantages with BB MRI and US as strong emerging alternatives to 3D CT.