Ventricular size measurement methods in fetuses considered for prenatal closure of myelomeningocele

Prenatal closure of myelomeningocele is associated with a reduced rate of hydrocephalus treatment. This need for hydrocephalus treatment is positively correlated with fetal ventricular width. When ventricular width is 15 mm or greater, the benefits of prenatal closure, as a method to decrease hydrocephalus treatment, are reduced. Thus, fetal ventricular size is an important factor when counseling families who are considering intrauterine surgery with mitigation of hydrocephalus as the primary goal. This study sought to determine whether imaging modality (ultrasound [US] vs MRI) and interobserver variability were factors in any ventricular size disparity seen on imaging studies.

The imaging studies of 15 consecutive fetuses who underwent prenatal myelomeningocele repair at Children's Mercy Fetal Health Center, Kansas City, Missouri, were reviewed. All fetuses were imaged with US and fetal MRI; on average (range), procedures were performed 3.8 (0-20) days apart. Three comparisons were performed to analyze interobserver and intermodality variability in ventricular width measurements: 1) retrospective comparison of dictated ventricular widths measured with MRI and US by pediatric radiologists (PRs) and maternal-fetal medicine specialists (MFMs), respectively; 2) blinded measurements obtained with US by PRs versus initial US-based measurements by MFMs, and blinded measurements obtained with MRI by PRs versus initial MRI-based measurements by PRs; and 3) blinded measurements obtained with MRI by PRs versus those obtained with US.

Retrospective comparison showed that measurements with MRI by PRs were on average 2.06 mm (95% CI 1.43-2.69, p < 0.001) larger than measurements with US by MFMs. Blinded measurements with US by PRs were on average larger than dictated measurements obtained with US by MFMs, but by only 0.6 mm (95% CI 0.31-0.84, p < 0.001). When PRs measured ventricular size in a blinded fashion with both US and MRI, the mean width determined with MRI was significantly larger by 2.0 mm (95% CI 1.26-2.67, p < 0.0001).

The ventricular width of these fetuses was larger when measured with MRI than US by an amount that could impact recommendations for fetal surgery. Every center involved in counseling families about the risks and benefits of fetal intervention for spina bifida needs to be aware of these possible imaging-based disparities.