First trimester ultrasonographic findings for spina bifida

Open spina bifida (OSB) is associated with the Arnold- Chiari II malformation, which is thought to be the consequence of leakage of cerebrospinal fluid into the amniotic cavity and hypotension in the subarachnoid spaces, leading to caudal displacement of the brain stem and obliteration of the cistern magna, was reported in 2009 to be recognized by first trimester ultrasound scan. 
Anechoic area in the forth ventricle entitled as intracranial translucency by Chaoui et al. which is between two echogenic line anteriorly dorsal side of brainstem and posteriorly choroid plexus of the fourth ventricle at mid sagittal plane which is used for the examining nuchal translucency and nasal bone in normal fetuses. But, in their retrospective studies, they couldn’t show this translucency area in few cases. Also prospective studies it is seen that same amount of fluid collection at this area on  cases with open spina bifida but this collection is not clear as normal cases.  Another first trimaster ultrasonographic finding for Spina Bifida is increased brainstem thickness due to replacing of brain towards to occipital bone and decreased distance between brainstem and occipital bone. In other words, ratio of brain stem thickness to brainstem – occipital bone distance  is greater than 1. 2  Another one for Spina Bifida is shortening of the distance between occipital bone and Aquaductus Sylvius at axial plane. Also decrease of biparietal distance due to the decrease of cerebrospinal fluid amount and facial degree shortening are seen.
As a result, absence or decrease of intracranial translucency, ratio of brain stem thickness to brainstem – occipital bone distance is greater than 1, shortening of the distance between occipital bone and Aquaductus Sylvius at axial plane, decrease of biparietal distance and shortening of facial degree are the major first trimester ultrasonographic findings for fetuses with open Spina Bifida

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