Fetal diffusion tensor quantification of brainstem pathology in Chiari II malformation

Area of Science:

• Neuroimaging
• Fetal Medicine
• Biophysics

Background:

• Prenatal diagnosis of central nervous system (CNS) abnormalities is crucial for management.
• Chiari II malformation is a complex congenital disorder often associated with hydrocephalus.
• Diffusion tensor imaging (DTI) offers insights into tissue microstructural development.

Purpose of the Study:

• To assess if DTI metrics can identify midbrain changes in fetuses with Chiari II malformations.
• To compare DTI findings in Chiari II malformations with those in fetuses with hydrocephalus, mild ventriculomegaly, and normal CNS development.
• To evaluate the potential of DTI in differentiating between various prenatal diagnoses causing enlarged ventricles.

Main Methods:

• Retrospective analysis of prenatal MRI scans from 46 normal fetuses, 15 with Chiari II, 8 with hydrocephalus, and 12 with mild ventriculomegaly.
• Calculation of fractional anisotropy (FA) and apparent diffusion coefficient (ADC) from midbrain regions of interest.
• Age-matched group comparisons using DTI sequences (b-values of 0 and 700 s/mm², 1.5 Tesla).

Main Results:

• Significantly higher FA in the midbrain of fetuses with Chiari II malformations compared to normal controls (p=0.003).
• No significant difference in ADC was observed between Chiari II and normal fetuses.
• No significant differences in FA or ADC were detected between normal controls and fetuses with hydrocephalus or mild ventriculomegaly.

Conclusions:

• DTI can detect and quantify parenchymal alterations in the fetal midbrain associated with Chiari II malformations.
• Elevated midbrain FA may serve as a biomarker to differentiate Chiari II malformation from other conditions causing enlarged fetal ventricles.
• This technique could potentially aid in diagnosing open neural tube defects and stratifying patients for prenatal interventions.