Open Spinal Dysraphism Without Hindbrain Herniation-Natural History and Postnatal Outcome.

Objective: To report the natural history of fetuses with open spinal dysraphism (OSD) without hindbrain herniation (HBH) during second-trimester evaluation.

Methods: A multicenter retrospective cohort study was conducted across three prenatal centers to evaluate fetuses with OSD. We reviewed cases with postnatally confirmed OSD without prenatal HBH at 19-27 weeks. Standardized prenatal evaluation consisted of repetitive ultrasound and magnetic resonance imaging. Postnatal outcome measures involved imaging, intraoperative findings and neurological function tests.

Results: Among 280 fetuses with OSD, evaluated at a median gestational age of 21 weeks, a total of 12 (4%) lacked HBH. Moderate ventriculomegaly was observed in 33% of cases without HBH. Corpus callosum anomalies were not detected. Postnatally, HBH was present in 50%, while the shunt rate remained low (20%). In 80%, postnatal motor function (MF) was equal to or better based on the anatomical level. In 33%, MF after birth declined in comparison to the first fetal functional assessment in the second trimester.

Conclusion: Fetuses with OSD and absent HBH in the second trimester demonstrate a low postnatal shunt rate. MF was frequently impaired at the initial second-trimester assessment, and in about a third of cases, postnatal MF seemed to have worsened. These findings may inform counseling and question the place of fetal surgery for this subgroup.