Embryonic development of the mammalian caudal Neural Tube

Abstract

In the literature, some controversy still exists about the embryonic developmental processes involved in the formation of the caudal neural tube. Therefore, a three-dimensional and histological study concerning the normal development of the caudal neural tube was performed on both mouse and human embryos. Three developmental processes can be distinguished in caudal neural tube development: caudal neuropore closure, secondary neurulation, and degeneration and differentiation of the secondary neural tube. Caudal neuropore closure occurs at the level of somite 32-34 in both species. Therefore, primary neurulation leads to the formation of all spinal cord segments and ganglia. Secondary neurulation involves cell deposition from a cluster of neurectodermal cells at the caudal end of the closed neural tube, directly around a lumen, the lumen always in contact with the lumen of the primary neural tube. This process leads only to the formation of the primordia of the filum terminale and ventriculus terminalis and, possibly, part of the conus medullaris. Secondary neurulation is followed by a period characterized by degeneration and differentiation of the secondary neural tube. Its lumen and neural tissue will disappear, whereas part of the secondary neurectodermal cells differentiate to a fibrous layer comparable and continuous with the marginal layer of the primary neural tube. This fibrous layer represents the future filum terminale. The embryological processes indicated above can be helpful in the interpretation of congenital anomalies affecting the caudal spinal cord and spine.

New classification of spinal lipomas based on embryonic stage

“…The caudal eminence gives rise to the caudal portion of the digestive tube, blood vessels, and the future somites of the S1-2 vertebral level and below-and eventually the spinal cord. [10][11][12][13] The caudal eminence fuses with the caudal neuropore and forms a solid cellular mass called the neural cord at POD 26, which then undergoes cavitation and connects to the central canal already present in the neural tube. By this process of cavitation, the solid neural cord transforms into a hollow secondary neural tube and fuses with the neural tube formed by primary neurulation into a continuous entity.…”

“…7,12 It is estimated that secondary neurulation continues until at least postovulatory Week 7. 13 In short, secondary neurulation occurs in 4 steps.…”

“…Closure of the caudal neuropore occurs first, followed by secondary neurulation and retrogressive degeneration of the secondary neural tube. 12 Recent studies suggest the presence of a unique process called "junctional neurulation," bridging the primary and secondary neurulations. 4 Presence of the junctional region between the primary and secondary neurulation has also been reported.…”

Dilation of the ventriculus terminalis: sonographic findings.

“…1,2 Neurulation, starting at the 3 week embryonic age, is responsible for formation of the neural tube by progressive closure of the neural plate and its separation from the overlying ectoderm. The distal cord develops from a caudal cell mass that forms from neural epithelium and notochord caudal to the primary neural tube.…”

Prenatal Development of the Human Central Nervous System, Normal and Abnormal

“…This cord subsequently becomes cavitated and connected with the more rostrally located neural tube. It has been shown that the medullary cord gives rise to the spinal cord caudal to the level of the 32nd to 34th somites (Nievelstein et al, 1993). This process is called secondary neurulation and is distinguished from primary neurulation that forms the brain and the most part of the spinal cord by means of neural tube closure.…”