PMC6402120_01
a-d Mid-sagittal T2-weighted 1.5 Tesla magnetic resonance images (a and c, Single-shot; b and d, Balanced Turbo Field Echo) of the fetal brain. At 21 weeks'gestation (a, b), the cerebellar vermis (a, black arrow) appears upwardly rotated and moderately hypoplastic with a normal torcular position (a, white arrow). At 27 weeks'gestation (c, d), the vermis appears nearly normal in position, shape and size suggesting delayed fenestration of Blake's pouch (a, asterisk) The primary (c, white arrow), prepyramidal (c, black arrow), and secondary (c, arrow head) fissures are roughly discernible. e A slight uncertainty regarding minimal hypoplasia of the cerebellar vermis (arrow) remains even after inconspicuous transcranial ultrasound postnatally at the age of 10 weeks
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Fig1
Magnetic resonance imaging using a Phillips 1.5 Tesla scanner revealed moderate rotation of the cerebellar vermis (Fig. 1a, b) which we believed was due to mild vermian hypoplasia. Rotation of the vermis was less pronounced at that time and, given a cross-sectional area of 103 mm2 on a mid-sagittal single-shot T2-weighted image, vermian hypoplasia was rated minimal if present at all (Fig. 1c, d). In postnatal transcranial ultrasound at the age of 10 weeks, the cerebellar vermis appeared normal (Fig. 1e).
PMC6402120_02
a-c Mid-sagittal (a, Half-Fourier Acquisition Single-Shot Turbo Spin-Echo [HASTE]; b, True Fast Imaging With Steady-State Free Precession) and axial (c, HASTE) T2-weighted 3 Tesla magnetic resonance (MR) images of the fetal brain at 21 weeks'gestation suggesting a moderately hypoplastic cerebellar vermis with a flattened fastigial point (b, arrow) and moderately increased tegmento-vermian angle of about 35 , but normal torcular position (a, arrow). Lateral septa (c, arrows) in the posterior fossa are believed to belong to Blake's pouch (c, asterisk). d, e Follow-up imaging on the same scanner at 31 weeks'gestation shows nearly normal rotation of the vermis in a slightly enlarged posterior fossa (d, arrow) suggesting delayed fenestration of Blake's pouch. Mild infero-posterior vermian hypoplasia (e, arrow) may be suspected from early third-gestational MR imaging (MRI) (d, e) This finding becomes more evident if compared to the sagittal T2 HASTE image of the cerebellar vermis (f, arrow) in a fetus at 24 weeks'gestation scanned for suspected pulomonary sequestration on the same MR system. g, h A similar pattern is depicted by postnatal sagittal MRI (g, T1 Magnetization-Prepared Rapid Gradient-Echo; h, T2 Turbo spin echo) at the age of 12 weeks. Size and shape of the cerebellar vermis imply that it is mildly hypoplastic and its posterior lobe has experienced mass effect due to prolonged persistence of Blake's pouch. Further, partial volume of cerebellar hemisphere (g, h; arrow heads) adjacent to the foramen of Magendie has to be considered. i For comparison of cerebellar volume and fissuration, the sagittal T1-weighted MR image in a 4-month-old, clinically inapparent infant scanned for a temporopolar arachnoid cyst - known from pre- and postnatal ultrasound - is given here
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Fig2
On MRI, the infero-posterior part of the cerebellar vermis appeared to be moderately hypoplastic (Fig. 2a, b). Dandy-Walker malformation (in the narrow sense) could be excluded (Fig. 2a). Follow-up images acquired on the same scanner at 31 weeks' gestation depicted a slightly pronounced cisterna magna and a nearly normalized tegmento-vermian angle (Fig. 2d, e). Tesla MRI at the age of 12 weeks confirmed the fetal imaging report, but did not add any relevant information (Fig. 2g, h). The boy was neurologically unremarkable at the age of 3 months.