Cerebral Diffusivity Changes in Fetuses with Chiari II Malformation

Objectives: Chiari II malformation is a congenital abnormality characterized by a small posterior fossa with downward displacement of the hindbrain into the foramen magnum. Diffusion-weighted imaging (DWI) can be used to quantitatively characterize brain injury and physiological maturation. We aim to evaluate DWI parameters of the infra- and supratentorial brain in fetuses with Chiari II malformation. Methods: MRI and US studies of 26 fetuses with Chiari II malformation and 15 controls were evaluated for the presence/severity of hydrocephalus, myelomeningocele level, and brain apparent diffusion coefficient (ADC) values. Cerebral flow impedance parameters (resistance and pulsatile indexes, resistance index [RI], and pulsatility index [PI] respectively) from concurrently preformed fetal US were also evaluated. Results: Of the Chiari II group, 16 fetuses had hydrocephalus. There was increasing severity of lateral ventriculomegaly in the high compared to low spinal dysraphism subgroups. There were significant lower ADC values in the frontal (p = 0.01) and temporal lobes (p = 0.05) in Chiari II group compared with normal, regardless of the presence or severity of hydrocephalus. Fetuses with Chiari II showed significantly lower RI and PI values. Conclusions: Abnormal ADC values indicate supratentorial microstructural changes in fetuses with Chiari II malformation. Further investigation of the role of diffusion imaging metrics in evaluating abnormal brain development, parenchymal damage and efficacy of fetal surgery is needed.