Objective: To investigate the role of the interpeduncular angle (IPA) as a new indicator of intracranial hypotension in fetuses with open spinal dysraphism (SD).Methods: Two groups of fetuses undergoing magnetic resonance imaging (MRI) examination were identified. The study group included fetuses with open SD (n ¼ 21), while the control group included fetuses with a normal brain and spine (n ¼ 43). Two observers retrospectively evaluated axial T2-weighted images of the brain and the IPA was identified and measured. Other features of the Chiari II malformation were also evaluated in the study group and correlated with the IPA. Results:The average value (�SD) of the IPA for the study and control groups was 9.8°� 18.5°and 60.2°� 5.9°, respectively. The intergroup analysis of the IPA measurements revealed a statistically significant difference between the groups (p < 0.005). Brainstem slumping or cerebellar tonsillar descent, collapse of the fourth ventricle, and ventriculomegaly also had a significant correlation with a lower IPA (p ¼ 0.001). Conclusion:Measuring the IPA may be a useful technique for assessing the degree of intracranial hypotension in fetuses with open SD. This technique can also detect less severe cases of prenatal intracranial hypotension, even before cerebellar tonsillar descent. The lower IPA in fetuses with open SD further supports the theory that cerebrospinal fluid leakage, and not traction, is the underlying cause of Chiari II malformation. Key pointsWhat's already known about this topic? � Open spinal dysraphism (SD) in the fetus is almost always associated with Chiari II malformation.� In these cases, the Chiari II malformation has been ascribed to the chronic leakage of cerebrospinal fluid through the spinal defect.� The interpeduncular angle (IPA) is significantly lower in adults with intracranial hypotension than individuals with normal intracranial pressure. What does this study add?� The IPA is significantly reduced in fetuses with open SD compared to controls.