Purpose: Chiari II malformation is a congenital abnormality characterized by a small posterior fossa with downward displacement of the hindbrain into the foramen magnum, almost exclusively associated with open spinal dysraphism. 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.
Material and methods: MRI and US studies of twenty-six fetuses with Chiari II malformation and fifteen controls were evaluated for presence/severity of hydrocephalus, myelomeningocele level, and ADC values of frontal, parietal and temporal lobes, pons and cerebellar hemispheres. Cerebral flow impedance parameters (resistance and pulsatile indexes, RI and 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 presence or severity of hydrocephalus. No significant ADC differences identified in the cerebellum and pons. 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, possibly secondary to altered CSF hydrodynamics related to CSF leakage through the open spinal dysraphism. Further investigation of the role of diffusion imaging metrics in evaluating abnormal brain development, parenchymal damage and efficacy of fetal surgery is needed.
