MRI Studies of the Fetal Brain and Cranium

Ultrasound is the primary modality for fetal imaging, but Magnetic Resonance Imaging nowadays has a valuable complementary role as it often reveals findings that alter pregnancy management. Knowledge on some clinically relevant areas of the normal fetal development is still lacking, and this was the aim of this project. We wanted 1) to obtain reference MRI data of normal brain measurements before 24 gestation weeks (GW), 2) to study the development of the hippocampus, 3) to study the development of the ear and 4) to test the ability of MRI for evaluating the lip and palate. For this, we retrospectively analysed a database with 464 in vivo and 21 post mortem fetal MRI examinations. Study I evaluated a series of 70 normal fetuses. A table of normal brain measurements from 17 to 23 GW was built, the first in the literature that includes ages below 20 GW. Study II focused on the evolution of the hippocampus from 18 to 38 GW by evaluating 3 post mortem and 60 in vivo MRI examinations. Our results suggested this area to develop later and more asymmetrically than previously thought. Study III analysed a series of 122 normal MRI in vivo and 16 MRI post mortem. We described the development of the fetal ear in vivo for the first time in the literature, realizing that the value of MRI is limited by the size of the structures evaluated. In study IV, 60 brain-targeted MRI examinations of 55 normal fetuses and 5 fetuses with orofacial clefts were blindly reviewed by two readers, focusing on the lips and palates. Our results suggest a high accuracy of MRI in the evaluation of this area, regardless of fetal age or previous ultrasound findings. This thesis brings new knowledge on the normal development of the fetal brain and cranium