Supra Occipital Flattening: A Key Sign for Antenatal Diagnosis of Isolated Sagittal Craniosynostosis.

Craniosynostosis is an isolated finding in most cases, involving either the metopic or the sagittal suture. It is detected only sporadically during prenatal ultrasound, in the third trimester for non-isolated cases. When synostosis of the sagittal suture occurs, head shape growth proceeds in an anteroposterior direction, leading to scaphocephaly (long, narrow, boat-shaped skull). Moreover, the reduced vertical growth of the skull vault causes a supra-occipital flattening, detectable at the profile view. Fetuses' head shape diagnosed as dolicocephalic should be carefully studied for the presence of the supra-occipital bone flattening; this sign may lead to the suspicion of a sagittal craniosynostosis.