A MAGNETIC-RESONANCE TEMPLATE FOR NORMAL NEURONAL MIGRATION IN THE FETUS

OBJECTIVE: Although the features of neuronal migration have been known since the turn of the century, the serial features of neuronal migrat ion as seen with magnetic resonance imaging (MRI) have not been descri bed. Our objective was to provide a template of the normal appearance and the temporal pattern of neuronal migration in the human fetal brai n early in the second trimester as seen with MR imaging and to correla te our findings with histological sections and atlases. METHODS: Twent y-eight normal fetal specimens, which ranged from 9 to 24 weeks of ges tational age, were imaged with a 1.5 T clinical MRI unit by use of con ventional spin echo, fast spin echo, and three-dimensional Fourier tra nsformation spoiled gradient refocussed pulse sequences. RESULTS: The three-dimensional Fourier transformation spoiled gradient refocussed p ulse sequence provided the highest resolution images of neuronal migra tion. At 13 weeks of gestational age, the germinal matrix was identifi ed. A five-layer pattern of the fetal forebrain, which included layers of neuroblast formation and migration, could be identified at 16 to 1 8 weeks by MRI. The germinal matrix and layers of migrating neurons di minished considerably in size by 21 weeks. Histological studies and co rrelation with anatomic atlases confirmed the MRI findings. CONCLUSION : Images obtained by use of MRI with standard clinical pulse sequences can document the appearance and the temporal patterns of neuronal mig ration in postmortem fetal specimens. With the evolution of high-resol ution MRI and faster scanning techniques, these findings may serve as a template for the in utero MRI appearance of neuronal migration and t hereby compliment the antenatal ultrasonic investigation of congenital anomalies.