Correspondence regarding research letter published by Arigita et al.

We congratulate Arigita and coworkers for their success in diagnosing open spina bifida in a 13-week fetus with normal intracranial translucency. Syngelaki et al., recently published that only three out of 21 cases (14%) of fetuses with open spina bifida were detected at 11–13weeks scan in a screening population of about 45 000 fetuses by direct examination of the fetal spine. Chaoui et al., were focusing to look at markers in the midsagittal view which is used anyway for measurement of nuchal translucency in screening for Down syndrome. Lachmann et al., showed that the measurement of the frontomaxillary angle is decreased in the majority of the fetuses with open spina bifida at 11–13weeks. Unfortunately the picture showing the measurement of the frontomaxillary angle in your research letter shows several criteria which make it not possible to measure the frontomaxillary angle regarding the criteria of the Fetal Medicine Foundation. The frontomaxillary facial angle is measured between a line along the upper surface of the palate and a line that traverses the upper corner of the anterior aspect of themaxilla, extending to the external surface of the forehead, represented by the frontal bones or an echogenic line under the skin below the metopic suture, which remains open at this gestational age. The line which traverses the upper corner of the anterior aspect of the maxilla, extending to the external surface of the forehead is placed in the presented picture anteriorly to the frontal bone to the skin. The midsagittal view of the fetal face at 11+ 0 to 13+6weeks’ gestation is defined by the presence of the echogenic tip of the nose and rectangular shape of the palate anteriorly, the translucent diencephalon in the center and the nuchalmembrane posteriorly. Deviations from the exactmidline plane result in non-visualization of the tip of the nose and visibility of the zygomatic process of the maxilla. The zygomatic process in the presented case is clearly visible; therefore, the employed method cannot be used in such a picture. However, in your presented case, the posterior brain seems to be abnormal: Our recently published study focusing on measurements of the posterior brain in the midsagittal view might improve the detection rate for open spina bifida because the posterior brain shows a brainstem diameter and brainstem to occipital bone diameter (BS-BSOB) ratio of above 1 in this case. This was also the case in all 30 fetuses with open spina bifida in our pilot study assessing this approach. However in a clinical screening process, the detection rate using such a method will never be 100%, such as the paper suggested. Therefore, it might be useful in cases where the ratio is smaller than 1 to use the measurement of the cisterna magna in the tilted axial view as described in our paper. The frontomaxillary angle in comparison to nasal bone, ductus venosus and tricuspid flow is so far the least-used additional marker in screening for Down syndrome at 11–13weeks perhaps because of the difficulties illustrated here. In our view, it might be useful and easier to use the ratio (BSBSOB ratio) calculated out of the measurements of brainstem diameter and brainstem to occipital bone diameter in the midsagittal view to increase the detection rate and decrease the false positive rate in screening for open spina bifida. A recently published prospective study using this approach confirms our findings.