Abstract
ObjectivesIn cases of “spina bifida,” a detailed prenatal imaging assessment of the exact morphology of neural tube defects (NTD) is often limited. Due to the diverse clinical prognosis and prenatal treatment options, imaging parameters that support the prenatal differentiation between open and closed neural tube defects (ONTDs and CNTDs) are required. This fetal MR study aims to evaluate the clivus-supraocciput angle (CSA) and the maximum transverse diameter of the posterior fossa (TDPF) as morphometric parameters to aid in the reliable diagnosis of either ONTDs or CNTDs.MethodsThe TDPF and the CSA of 238 fetuses (20–37 GW, mean: 28.36 GW) with a normal central nervous system, 44 with ONTDS, and 13 with CNTDs (18–37 GW, mean: 24.3 GW) were retrospectively measured using T2-weighted 1.5 Tesla MR -sequences.ResultsNormal fetuses showed a significant increase in the TDPF (r = .956; p<.001) and CSA (r = .714; p<.001) with gestational age. In ONTDs the CSA was significantly smaller (p<.001) than in normal controls and CNTDs, whereas in CNTDs the CSA was not significantly smaller than in controls (p = .160). In both ONTDs and in CNTDs the TDPF was significantly different from controls (p<.001).ConclusionsThe skull base morphology in fetuses with ONTDs differs significantly from cases with CNTDs and normal controls. This is the first study to show that the CSA changes during gestation and that it is a reliable imaging biomarker to distinguish between ONTDs and CNTDs, independent of the morphology of the spinal defect.
Highlights
The prenatal differentiation between open (ONTDs) and closed neural tube defects (CNTDs) of the spine is crucial because postnatal prognoses differ considerably
The diagnoses could be confirmed in 44 cases of ONTDs and in 13 cases of CNTDs by postnatal surgery or postmortem examination
Terminations of pregnancy were performed in 24 fetuses with ONTDs between 18 and 35 GW based on the diagnoses established using fetal ultrasound and MRI and on maternal afetoprotein levels
Summary
The prenatal differentiation between open (ONTDs) and closed neural tube defects (CNTDs) of the spine is crucial because postnatal prognoses differ considerably. The differentiation based on MRI findings of the neural tube defect (NTD) can be impeded by limited depiction and distinction of the anatomical structures at the site of the NTD, especially in early second-trimester fetuses due to limited spatial resolution. Various imaging signs of a morphologically abnormal posterior fossa have been described by ultrasound. These non-quantitative criteria comprise the banana sign [7,8,9], an effaced cisterna magna [10], bilateral downward-triangle shape (triangle sign), quadrilateral angular shape (square sign) of the lateral ventricles, [11] and absence of the translucency of the fourth ventricle [12]
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