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A case of limited dorsal myeloschisis located at the area of secondary neurulation. The spinal cord and adjacent structure below the S1-2 junction are believed to originate from secondary neurulation. The inset shows a typical cigarette-burn skin lesion.
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Compared to any other decade, the last two decades have been the most dynamic period in terms of advances in the knowledge on spinal dysraphism. Among the several factors of rapid advancement, such as embryology during secondary neurulation and intraoperative neurophysiological monitoring, there is no doubt that Professor Dachling Pang stood high a...
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Citations
... It proceeds by condensation, cavitation, canalization, and regression of the medullary cord [6]. The regression phase forms the conus medullaris and filum terminale [7][8][9]. Studies have been conducted using animal models to assess late secondary neurulation, regression phase, and associated anomalies. In particular, we previously showed changes in the development of terminal balloons in chick embryos based on similarity with terminal myelocystocele (TMCC) [10]. ...
The caudal portion of the spinal cord, the medullary cord, is formed by secondary neurulation. One of the distinctive features of secondary neurulation compared to primary neurulation is that the medullary cord normally degenerates into a filum in humans. Various anomalies have been known to originate from degenerating process errors. One anomaly is terminal myelocystocele (TMCC), which is a closed spinal dysraphism with an elongated caudal spinal cord. The terminal part is filled with cerebrospinal fluid (CSF) and protrudes into the dorsal extradural space. Another anomaly is the retained medullary cord (RMC), which is a nonfunctioning cord-like structure extending to the cul-de-sac. In a 1-month-old boy, we identified an RMC with cystic dilatation of the caudal end extending to the epidural space at the very bottom of the cul-de-sac, resembling a degenerating terminal balloon, which is an essential feature of TMCC. Hence, this case may be considered an intermediate form between TMCC and RMC. This case provides clinical evidence that TMCC and RMC share the same pathoembryogenic origin, namely, failure of the regression phase of secondary neurulation.
... The advancement of knowledge on secondary neurulation, in addition to the development of technology such as intraoperative neurophysiological monitoring (IONM) and new pioneers in this field, has led to dramatic changes in the understanding and management techniques in occult spinal dysraphism seen in the last two decades 62) . ...
Recent advancements in basic research on the process of secondary neurulation and increased clinical experience with caudal spinal anomalies with associated abnormalities in the surrounding and distal structures shed light on further understanding of the pathoembryogenesis of the lesions and led to the new classification of these dysraphic entities. We summarized the changing concepts of lesions developed from the disordered secondary neurulation shown during the last decade. In addition, we suggested our new pathoembryogenetic explanations for a few entities based on the literature and the data from our previous animal research. Disordered secondary neurulation at each phase of development may cause corresponding lesions, such as failed junction with the primary neural tube (junctional neural tube defect and segmental spinal dysgenesis), dysgenesis or duplication of the caudal cell mass associated with disturbed activity of caudal mesenchymal tissue (caudal agenesis and caudal duplication syndrome), failed ingression of the primitive streak to the caudal cell mass (myelomeningocele), focal limited dorsal neuro-cutaneous nondisjunction (limited dorsal myeloschisis and congenital dermal sinus), neuro-mesenchymal adhesion (lumbosacral lipomatous malformation), and regression failure spectrum of the medullary cord (thickened filum and filar cyst, low-lying conus, retained medullary cord, terminal myelocele and terminal myelocystocele). It seems that almost every anomalous entity of the primary neural tube may occur in the area of secondary neurulation. Furthermore, the close association with the activity of caudal mesenchymal tissue in secondary neurulation involves a wider range of surrounding structures than in primary neurulation. Although the majority of the data are from animals, not from humans and many theories are still conjectural, these changing concepts of normal and disordered secondary neurulation will provoke further advancements in our management strategies as well as in the pathoembryogenetic understanding of anomalous lesions in this area.
Retained medullary cord (RMC) is a defect resulting from impaired secondary neurulation. Intraoperatively, RMC is recognizable as an elongated cord-like structure caudal to the conus, that contains histologically confirmed neuroglial components and a lumen with an ependymal lining. It characteristically does not possess neurological function. This chapter aims to summarize (1) the mechanisms that lead to the occurrence of RMC; (2) the various forms of RMC, such as cystic RMC and ‘possible RMC’, and (3) the treatment strategies, especially untethering through limited exposure.KeywordsApoptosis arrestRetained medullary cordSecondary neurulationTethered cord
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Keywords: Diversity in neurosurgery, Gender equality, History of neurosurgery, Women in neurosurgery, Women in surgery
Recently, advanced knowledge on secondary neurulation and its application to the clinical experience have led to the deeper insight into the pathoembryogenesis of secondary neurulation with new classifications of the caudal spinal dysraphic entities. Here, we summarize the dynamic changes in the concepts of disordered secondary neurulation over the last two decades. In addition, we suggest our new pathoembryogenetic explanations for a few entities based on the literature and the data from our previous animal research. Disordered secondary neurulation at each phase may cause various corresponding lesions, such as (1) failed junction with the primary neural tube (junctional neural tube defect and segmental spinal dysgenesis), (2) dysgenesis or duplication of the caudal cell mass associated with disturbed activity of caudal mesenchymal tissue (caudal agenesis and caudal duplication syndrome), (3) abnormal continuity of medullary cord to the surrounding layers, namely, failed ingression of the primitive streak to the caudal cell mass (myelomeningocele), focal limited dorsal neurocutaneous nondisjunction (limited dorsal myeloschisis and congenital dermal sinus), and neuro-mesenchymal adhesion (lumbosacral lipomatous malformation), and (4) regression failure spectrum of the medullary cord (thickened filum and filar cyst, retained medullary cord and low-lying conus, terminal myelocele, and terminal myelocystocele). It seems that almost every anomalous entity of the primary neural tube may occur in the area of secondary neurulation. Furthermore, the close association of the caudal cell mass with the activity of caudal mesenchymal tissue involves a wider range of surrounding structures in secondary neurulation than in primary neurulation. Although the majority of the data are from animals and many theories are still conjectural, these changing concepts of normal and disordered secondary neurulation will provoke further advancements in our management strategies as well as in the pathoembryogenetic understanding of anomalous lesions in this area.KeywordsSecondary neurulationCaudal cell massMedullary cordCaudal mesenchymal tissueAnomalyEmbryology
Background
There is a vast amount of published articles, centered on tethered cord syndrome, which is related to a constellation of diverse pathological entities, included under the term occult spinal dysraphism.
Objective
To present the 100 most-cited articles dedicated to the entity of tethered cord syndrome and to present a comprehensive review of the relevant literature.
Methods
In April 2020, we executed a title- focused search using Thomson Reuters Web of Science database in order to identify the most cited articles relevant to tethered cord syndrome. Consequently, we reviewed the results to certify that they were relevant to the criteria of our research protocol. The 100 most cited papers were chosen and further analyzed.
Results
Our search resulted in 769 articles, published from 1976 until now. All of them combined, have been cited 5.340 times, in a total of 2.097 different articles, with an average citation per item of 53.4.The most cited article was published by Yamada S., in 1981, while the last in our list was published by Walton, M et al in 1995.
Conclusions
We distinguished the top 100 most-cited articles dedicated to tethered cord syndrome, all of which are demonstrating important aspects and conclusions, being well-supported and methodologically fully adequate. We also reviewed the relevant evolution of the concept of management and the knowledge of the natural history, as well as new data in tethered cord syndrome research, alongside with the relevant contributions of different authors, fields of special interest, and countries.
