SYDNEY, AUSTRALIA – The brain shadowing sign – a sharply demarcated area of acoustic shadowing on ultrasound – is a novel and easily identifiable marker for fetal craniosynostosis, a small multicenter retrospective study showed.
An analysis of ultrasound images from 16 patients with a postnatal diagnosis of fetal craniosynostosis, presented at the International Society of Ultrasound in Obstetrics and Gynecology world congress, showed the brain shadowing sign was clearly depicted in all cases, even when the suture was only partly closed.
Coauthor Gustavo Malinger, director of the ob.gyn. ultrasound unit at the Tel Aviv Sourasky Medical Centre, said prenatal diagnosis of fetal craniosynostosis is often difficult, particularly if it involves the sagittal suture and occurs in the absence of a family history. As a result, most cases are delivered without a diagnosis.
"With the metopic suture, you have a chance to make a diagnosis because the shape of the head is quite characteristic. So with the third-trimester examination, when you perform a weight estimation or something like that, you see that something is wrong," Dr. Malinger said in an interview.
"But when the sagittal suture is closed, you don’t see it because you come from the side; you obtain axial planes and you never reach the sagittal suture."
The brain shadowing sign occurs because of a failure of the acoustic wave to cross the cortical bone, and appears as a line separating a zone of clearly defined brain anatomy and a zone of relative shadow.
The sign is easily identifiable, is not dependent on fetal position, and does not require visualization with high-definition 3D transducers.
All patients underwent a multiplanar neurosonographic exam with transvaginal and transabdominal ultrasound.
The mean gestational age at diagnosis was 29 weeks, and the diagnosis was made in the second trimester in only five cases. Dr. Malinger said that while it was possible in some cases to diagnose very severe cases at 22 weeks, fetal craniosynostosis tends to develop later in the pregnancy.
Prenatal diagnosis did not necessarily enable any kind of intervention, he added, but it was important in enabling counselling to be provided to families to prepare them for what to expect.
"They are ready to know, and we send them to a neurosurgical consultation in utero, so the neurosurgeon can explain that in most of the cases, it’s going to be OK, and that we’ll follow up," Dr. Malinger said.
Of the 16 patients included in the study, 14 presented with single-suture craniosynostosis: 6 involved metopic suture; 5, sagittal suture; and 3, coronal suture.
Nine cases were isolated fetal craniosynostosis, three were cases of Apert syndrome, and four also presented with associated CNS and non-CNS anomalies.
Dr. Malinger said the earlier diagnosis of fetal craniosynostosis could enable discovery of other related malformations that might otherwise have been missed.
No financial conflicts were reported.