Presentation
Suspicion of mega cisterna magna on 2nd trimester ultrasound.
Patient Data
Normal fetal brain at 24 weeks gestation. No mega cisterna magna or other posterior fossa abnormality.
Normal, gestation appropriate sulcation is shown. Note calcarine and parietooccipital sulci on medial aspect of hemispheres on coronal and axial images respectively. Sylvian fissure opercularization has progressed and early evidence of central sulcus noted on sagittal images. Normal vermis foliation is present on the midline sagittal spoiled gradient echo image. This is also a nice example of normal, five-layered lamination.
Sagittal acquisition somewhat oblique, but was the best possible.
Normal fetal body MRI at 24 weeks. Note the utility of T1 fat saturated acquisition for the visualization of fetal bowel (T1 hyperintense meconium) and of the thyroid gland (also T1 bright).
Key findings at 24 weeks gestation. The central sulcus is now becoming visible. Normal foliation of the cerebellar vermis nicely depicted, and note visualization of the pituitary stalk. 5 layered laminar appearance is still seen.
Ventricular zone (curved arrow); 2. periventricular fiber-rich zone (dotted arrow); 3. intermediate zone (straight long arrow); 4. sub-plate (fuzzy arrow); 5. cortex (short thick arrow)
Case Discussion
Normal fetal MRI at 24 weeks gestation, demonstrating the key cerebral features seen at this stage. Compare with the normal fetal MRI at 22 weeks gestation for interval progression.
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