Neurulation and the origin of open and closed spinal bifida

Neurulation and the origin of open and closed spinal bifida: (a) Schematic transverse sections showing the process of primary neurulation, which involves bending of the neural plate, convergence of the neural folds and closure of the neural tube. (b) A histological section through the open spinal neural folds of an unaffected human embryo (Carnegie stage 12, 26 days post-fertilization), showing the closing neural tube during primary neurulation. (c) Failure of the neural groove to close in the low spinal region in the fourth week after fertilization leads to myelomeningocele (also termed open spina bifida). (d) Schematic sagittal sections showing the process of secondary neurulation, which involves condensation of the caudal eminence, followed by the formation of the lumen (canalization), completion of secondary neurulation and regression of the tail. This process finalizes in the sixth week after fertilization. (e) A histological section through an unaffected human embryo (Carnegie stage 13, 30 days post-fertilization), showing formation of the secondary neural tube (nt) through canalization. (f) Failure of the secondary neural tube to separate from non-neural tissues (tethering) leads to closed spinal dysraphism, in this case with massive lipoma. no, notochord; np, neural plate; so, somite. | Spina bifida. (2015). Nature Reviews Disease Primers, 1, 15051. Retrieved from http://dx.doi.org/10.1038/nrdp.2015.51