Region-specific changes in brain diffusivity in fetal isolated mild ventriculomegaly.

OBJECTIVES: To evaluate the impact of symmetric and asymmetric isolated mild ventriculomegaly (IMVM, atrial width 10-15 mm) on apparent diffusion coefficient (ADC) values in fetal brain areas. METHODS: Sixty-seven sequential fetal head magnetic resonance imaging scans (feMRI) of VM cases performed between 2009 and 2014 were compared to 38 normal feMRI scans matched for gestational age (controls). Ultrasound- and MRI-proven IMVM cases were divided into asymmetrical (AVM, ≥2 mm difference in atrial width), symmetrical (SVM, <2 mm difference in atrial width), and asymmetrical IMVM with one normal-sized ventricle (AV1norm). RESULTS: ADC values were significantly elevated in the basal ganglia (BG) of the SVM and AV1norm groups compared to controls (p < 0.004 and p < 0.013, respectively). High diffusivity was constantly detected in the BG ipsilateral to the enlarged atria relative to the normal-sized atria in the AV1norm group (p < 0.03). Frontal lobe ADC values were significantly reduced in the AVM and SVM groups (p < 0.003 and p < 0.003 vs. controls). Temporal lobe ADC values were significantly reduced in the AVM group (p < 0.001 vs. controls). CONCLUSION: Isolated mild ventriculomegaly is associated with distinct ADC value changes in different brain regions. This phenomenon could reflect the pathophysiology associated with different IMVM patterns. KEY POINTS: Various ventriculomegaly patterns are associated with distinct diffusional changes. Frontal and temporal lobe ADC values are altered bilaterally, even in asymmetric ventriculomegaly. Basal ganglia ADC values are elevated ipsilateral to the enlarged ventricle.

Regional apparent diffusion coefficient values in 3rd trimester fetal brain.

INTRODUCTION: Apparent diffusion coefficient (ADC) values in the developing fetus can be used in the diagnosis and prognosis of prenatal brain pathologies. To this end, we measured regional ADC in a relatively large cohort of normal fetal brains in utero. METHODS: Diffusion-weighted imaging (DWI) was performed in 48 non-sedated 3rd trimester fetuses with normal structural MR imaging results. ADC was measured in white matter (frontal, parietal, temporal, and occipital lobes), basal ganglia, thalamus, pons, and cerebellum. Regional ADC values were compared by one-way ANOVA with gestational age as covariate. Regression analysis was used to examine gestational age-related changes in regional ADC. Four other cases of CMV infection were also examined. RESULTS: Median gestational age was 32 weeks (range, 26-33 weeks). There was a highly significant effect of region on ADC, whereby ADC values were highest in white matter, with significantly lower values in basal ganglia and cerebellum and the lowest values in thalamus and pons. ADC did not significantly change with gestational age in any of the regions tested. In the four cases with fetal CMV infection, ADC value was associated with a global decrease. CONCLUSION: ADC values in normal fetal brain are relatively stable during the third trimester, show consistent regional variation, and can make an important contribution to the early diagnosis and possibly prognosis of fetal brain pathologies.