First-Trimester Visualization Of The Fourth Ventricle In Fetuses With And Without Spina Bifida Editorial Comment

A recent retrospective study reported that the fourth ventricle cannot be visualized at the time of the first-trimester nuchal translucency ultrasound in fetuses with spina bifida. Confirmation of this finding could potentially provide the basis for first-trimester spina bifida screening in fetuses. However, data from 2 case reports did not confirm these results.The aim of this retrospective study was to determine the screening efficacy of first-trimester evaluation of the fourth ventricle for detection of spina bifida. The presence or absence of the fourth ventricle was determined by 4 blinded experienced prenatal diagnosticians who analyzed 250 digitally stored sonographic images (245 normal and 5 randomly interspersed spina bifida cases) at gestational ages of 11 weeks to 13 weeks 6 days. After identification of the fourth ventricle, its anteroposterior ventricular diameter was measured. The mean ventricle size was then related to the crown-rump length and gestational age by linear regression and Pearson correlation analysis.Among the 1000 images examined, the fourth ventricle was identified in 971 (97.1%). The sensitivity of an absent fourth ventricle in identifying spina bifida was 0.45 (false-negative rate: 55%, 11/20), whereas the specificity was 0.98 (false-positive rate: 2%, 20/980). False-negative and false-positive results were evenly distributed through the range of gestational ages. When measurable, mean ventricular size increased linearly with gestational age; its size was below the fifth percentile in 10 of 245 (4.0%) normal and 0 of 4 spina bifida cases. Using the 2-way analysis of variance model, intraclass correlation coefficient estimates were found to be 0.30 for a single rater and 0.64 for the mean of 4 raters.These findings suggest that nonvisualization of the fourth ventricle with first-trimester screening is a less robust marker for spina bifida than is suggested by previously published data.