Open spina bifida in the first trimester: intracranial translucency and sonographic markers of the posterior fossa
Assessment of Intracranial Translucency (IT)
Intracranial translucency (IT) is applied to detect open spina bifida during scanning at 11–13 weeks. Assessment of the posterior brain region can be performed in both the mid-sagittal and axial planes (Chaoui R, Nicolaides KH, Ultrasound Obstet Gynecol 2011). The original work on the application of IT in the detection of spina bifida is presented in the ISUOG Practice Guidelines for performing 11–14-week scanning (2023).
Additional First-Trimester Sonographic Markers
In addition to IT, the following markers have been proposed for detecting open spina bifida at 11–13 weeks:
| Marker | Source |
|---|---|
| Crash sign — first-trimester sonographic marker of spina bifida | Ushakov F et al., Ultrasound Obstet Gynecol 2019; 54: 740–745 |
| Ratio of fetal choroid plexus to head size | Chaoui R et al., Ultrasound Obstet Gynecol 2020; 55: 81–86 |
| Choroid bar — marker of normal posterior fossa at 12–14 weeks | Paladini D et al., Ultrasound Obstet Gynecol 2023; 63(4): 497–501 |
Associated Intracranial Changes
Perforation of the cavum septi pellucidi has been described in open spina bifida and is considered in relation to the need for hydrocephalus treatment by 1 year of life (Sanz Cortes M et al., Ultrasound Obstet Gynecol, Vol. 63, No. 1, 2024). Prenatal diagnosis of open and closed spina bifida is discussed in the work by Ghi T, Pilu G, Falco P et al. (Ultrasound Obstet Gynecol 2006; 28: 899–903).
Place in the Screening Protocol
Anatomical survey at 11–13 weeks according to the ISUOG protocol is aimed at detecting structural anomalies in fetuses with normal karyotype (Petousis S et al., J Matern Fetal Neonatal Med 2020; 33: 2581–2587). An overview of the capabilities of sonographic detection of open spina bifida in the first trimester is presented by Meller C, Aiello H, Otano L (Childs Nerv Syst 2017; 33: 1101–1106). Specific numerical thresholds for normal IT and the specified ratios are not provided in the source fragments [to be clarified].
Frequently asked questions
In which plane should the posterior brain region be assessed when searching for spina bifida?
According to Chaoui R, Nicolaides KH (Ultrasound Obstet Gynecol 2011), intracranial translucency and the posterior brain region can be assessed in both the mid-sagittal and axial planes.
What additional first-trimester markers are used in addition to IT?
The crash sign (Ushakov F et al., 2019), the ratio of choroid plexus to head size (Chaoui R et al., 2020), and the choroid bar as a marker of normal posterior fossa at 12–14 weeks (Paladini D et al., 2023).
Are there intracranial changes associated with prognosis in open spina bifida?
Perforation of the cavum septi pellucidi has been described in open spina bifida, associated with the need for hydrocephalus treatment by 1 year of life (Sanz Cortes M et al., UOG Vol. 63, No. 1, 2024).
At what gestational age is screening for open spina bifida performed in the first trimester?
Assessment of IT and posterior brain region markers is performed during scanning at 11–13 weeks; the protocol within the 11–14-week ultrasound is described in the ISUOG Practice Guidelines (2023).