Comment on the paper 'Spina bifida in a 13-week fetus with a normal intracranial translucency' published in Prenatal Diagnosis by Arigita et al. 2011.

We read with interest the report of. 1 The fact that the lumbosacral spina bifida was detected by directly visualizing the spine at 13weeks in a low-risk patient shows high quality of scanning in the ultrasound unit reporting. Unfortunately, in most centers, performing 11–13-week screening, open spina bifida (OSB) is not usually detected at this early stage 2,3 but at the second trimester scan where the indirect cranial signs including ‘lemon’ and ‘banana’ signs are evident. To improve the detection of OSB in early gestation, we have recently focused our efforts on the demonstration of indirect signs that can be detected at 11–13weeks. We have reported that in fetuses with OSB, there are abnormalities in the posterior brain and these are easily detectable in the same midsagittal view of the head as routinely used in first trimester screening for aneuploidies by measurement of fetal nuchal translucency thickness and assessment of the nasal bone. These abnormalities include obliteration of the fourth ventricle and/or cisterna magna with downward and backward displacements of the posterior brain. In this journal, we recently reported that there is, in addition, an increase in the diameter of the brain stem (BS), a decrease in the distance between the brain stem and occipital bone (BSOB), which contains the fourth ventricle and cisterna magna, and the BS to BSOB ratio is increased to more than 1. Arigita et al. described a case of OSB with an apparently normal fourth ventricle. We agree that, in some cases of OSB, there is some fluid in the fourth ventricle, but this does not correspond to a normal finding; the figure in their article does show that the posterior border of the intracranial translucency is the occipital bone rather than the floating choroid plexus of the fourth ventricle. Careful analysis of their figure confirms our observations that, in OSB, the posterior brain is abnormal: the diameter of the BS is increased, the choroid plexus of the fourth ventricle is not clearly visible, and the cisterna magna is obliterated. Consequently, the BS to BSOB ratio is increased to more than 1. The authors of the article were probably not aware