Unilateral coronal synostosis: can we trust the sagittal suture as a landmark for the underlying superior sagittal sinus?

OBJECTIVE The sagittal suture is usually considered an external anatomical landmark, indicating the location of the superior sagittal sinus (SSS) for surgical approaches. Children with unilateral coronal synostosis (UCS) often present with an important deviation of the sagittal suture. Because these patients usually undergo frontal reconstruction or even endoscope-assisted minimally invasive procedures, it is imperative to know the location of the SSS. The aim of this investigation was to study the anatomical relationship between the SSS and the sagittal suture in children with anterior plagiocephaly. METHODS The authors retrospectively studied the relationship between the sagittal sinus and the sagittal suture at 5 points: nasion, midpoint nasion-bregma, bregma, midpoint bregma-lambda, and lambda. The study analyzed CT scans of 50 children with UCS admitted to the craniofacial unit of Necker Enfants Malades Hospital between March 2006 and March 2013 and compared them with 50 control children with no evidence of craniosynostosis, bone disease, or genetic syndromes. The authors also analyzed the presence of extracerebral fluid collection and ventricular asymmetry in children with UCS. RESULTS Fifty-six percent of patients had anterior right UCS and 44% had left-sided UCS. Type I UCS was seen in 1 patient, Type IIA in 20 patients, Type IIB in 20 patients, and Type III in 9 patients. The authors found that the nasion is usually deviated to the ipsilateral side of the synostosis, the bregma contralaterally, and the lambda ipsilaterally. The gap distances between the reference point and the SSS were 0-7.3 mm (mean 1.4 mm) at the nasion; 0-16.7 mm (mean 3.8 mm) at the midpoint nasion-bregma; 0-12 mm (mean 5.8 mm) at the bregma; 0-9.5 mm (mean 3 mm) at the midpoint bregma-lambda; and 0-11.6 mm (mean 5.5 mm) at the lambda. Conversely, a discrepancy of more than 1 mm between the SSS and the position of the suture was found only in 7 control cases (14%). Of patients with UCS, 38% presented with an extracerebral fluid collection contralateral to the fused coronal suture. Fifty-two percent had a ventricular asymmetry, which was characterized by reduced ventricular volume ipsilateral to the synostosis in all but 1 patient. CONCLUSIONS In this study, the SSS was usually deviated contralaterally to the closed coronal suture. It tended to be in the midline of the cranial vault and could be projected virtually along an imaginary line passing through the midline of the cranial base. The authors recommend a distance of 37 mm from the sagittal suture as a safety margin during surgery.