PRENATAL-DIAGNOSIS OF NEURAL-TUBE DEFECT BEFORE 12 WEEKS GESTATION - DIRECT AND INDIRECT ULTRASONOGRAPHIC SEMIOLOGY

We describe the direct and indirect ultrasonographic features of a cas e of lumbar open spina bifida. The spinal defect was the prominent fea ture at 10 weeks + 5 days' gestation; however, cranial signs including narrowing of the frontal bones and flattening of the occiput were hel pful at 12 weeks. This 'acorn' sign is likely to precede the 'lemon' s ign, describing scalloping of the frontal bones at a later gestation. The diagnosis of spina bifida was confirmed by electrophoresis of the amniotic fluid, which showed an abnormal migration of acetylcholineste rase. Postmortem ultrasound examination of the same fetus proved usefu l in refining the diagnosis and also revealed the presence of the Arno ld-Chiari malformation. Development of ultrasound screening in the fir st trimester of pregnancy should allow further evaluation of these fin dings. It seems reasonable to confirm such an early diagnosis by elect rophoresis of the amniotic fluid as an alternative 50 ultrasonographic confirmation at 13-14 weeks.