Fig. 1

a, b Normal anatomy of the neural tube. Normal cranial bone structures. Fetus at 24 weeks’ gestation. a Sagittal and b coronal T2-weighted HASTE images of the fetal head show the osseous structures of the base of the skull (arrows in a) and bones of the cranial vault (arrows in b). c–f Normal fetal spine. Fetus at 27 weeks’ gestation. c Sagittal T2-weighted HASTE image of the spinal canal. The vertebral bodies are hypointense with a band of higher intensity in the centre (white arrows), the intervertebral spaces are hyperintense (black arrows). The ellipse marks the medullary cone. d Coronal T2-weighted HASTE image shows the vertebral pedicles as hypointense rounded structures on both sides of the spinal canal (arrowheads). The interpedicular distance in the lumbar spine is slightly increased (arrows); this is a normal finding that should not be confused with spina bifida. A false cervicothoracic scoliosis is also seen (black arrow). e Axial image at the level of L1–L2 shows the medullary cone (white arrow) inside the spinal canal (the asterisks mark the kidneys). f The medullary cone is no longer seen in this axial image of the spinal canal below the kidneys; sometimes the nerve roots can be identified (white arrows)