Commonly, craniosynostosis is present at birth, but it is not always diagnosed when mild. Usually it is diagnosed as a cranial deformity in the first few months of life. The diagnosis relies on physical examination and radiographic studies, including plain radiography and computed tomography (CT). Clinical history should include complications of pregnancy, duration of gestation, and birth weight 1).
Premature fusion of the cranial sutures restricts cranial growth perpendicular to the affected suture with compensatory overgrowth along the other patent sutures. This results in the characteristic skull shape deformities noted in craniosynostosis. Diagnostic imaging is necessary to confirm the fused suture and to assess the accompanying skull deformities, intracranial pathology and other complications. A prematurely fused suture shows perisutural sclerosis, linearity, reduced serration, bony bridging or the absence of the suture on a plain skull radiography or CT image. Secondary signs of increased ICP, such as a “copper-beaten” appearance, are also observed in severe cases 2).
Soboleski et al. 3) reported the ultrasonographic findings of craniosynostosis as follows : 1) the loss of the hypoechoic fibrous gap between hyperechoic body plates; 2) an irregular, thickened inner sutural margin; 3) the loss of a beveled edge; and 4) asymmetric fontanels. On “Black Bone” MRI, the affected fused sutures are demonstrated as absence of suture 4).
A normal patent suture is demonstrated as a radiolucency, serrated and nonlinear line on plain skull radiography and 3D-CT images 5) 6) 7) 8).
Ultrasonography shows a normal patent suture as an uninterrupted hypoechoic fibrous gap between hyperechoic cranial bones with an end-to-end appearance on a transverse scan of the sagittal sinus and a beveled appearance on a transverse scan of the coronal and lambdoid sutures 9) 10) 11)
Conventional MRI has typically been unreliable in identifying sutures individually. However, Eley et al. described a novel gradient echo MRI sequence (“Black Bone”) that minimizes soft tissue contrast to enhance the bone-soft tissue boundaries and can demonstrate normal patent cranial sutures as hyperintensity distinguished from the signal void of the cranial bones 12).
Proisy et al. from Rennes first described a high-resolution sonography technique and its limitations. They then analyzed the reliability, effectiveness and role of ultrasonography in routine practice using a PubMed literature review.
Ten studies reported excellent correlations between ultrasonography and 3D-CT. Cranial US for the diagnosis of a closed suture had 100% sensitivity in 8 studies and 86-100% specificity before the age of 12 months. Negative findings mean imaging investigation can be stopped. If ultrasonography confirms diagnosis, neurosurgical consultation is required. Thus, 3D-CT can be postponed until appropriate before surgery.
Cranial suture ultrasound is an effective and reliable technique for the diagnosis of craniosynostosis. It has many advantages: it is fast and non-irradiating, and no sedation is required. It should be used as first-line imaging in infants below the age of 8-12 months when craniosynostosis is clinically suspected. 13).