First trimester supratentorial and infratentorial abnormalities in fetuses with open spina bifida

Abstract

Objectives To examine whether supratentorial, infratentorial, and calvarial manifestations of open spina bifida (OSB) occur in the first-trimester. Methods Supratentorial (midbrain curvature, thalamic height), infratentorial (fourth ventricle diameter, brain-stem diameter [BSD], ratio of BSD to BSD-occipital bone diameter [BSOB]), and calvarial (frontomaxillary facial [FMF] angle) parameters were measured in stored midsagittal facial images at 110–136 weeks of 500 normal and 10 open spina-bifida fetuses by 3 blinded examiners. Results OSB fetuses displayed a larger midbrain curvature (93.26 ± 6.97 versus 97.79 ± 10.04, p < .05), decreased FMF angle (84.10 ± 5.44 versus 78.46 ± 5.82, p < .001), smaller fourth ventricle diameter (0.25 ± 0.04 mm versus 0.18 ± 0.05 mm, p < .001), smaller BSD (0.29 ± 0.04 mm versus 0.23 ± 0.04 mm; p < .001), and increased BSD to BSOB ratio (0.64 ± 0.71 versus 0.73 ± 0.93, p < .03) than normal controls, respectively. Thalamic height was not significantly altered. Detection rates of OSB were highest for fourth ventricle diameter and FMF angle (60% and 40%, respectively, at 95% specificity). BSD, BSD to BSOB ratio, midbrain curvature yielded sensitivities of 30% with 95% specificity. Two-dimensional discrimination for pairs of measures combining fourth ventricle diameter with FMF angle increased sensitivity to 90% with specificity of 90.7%. Conclusions Our findings suggest that supratentorial, infratentorial, and calvarial changes consistent with the Chiari-II malformation are already established in first-trimester fetuses with OSB.