Do junctional neural tube defect and segmental spinal dysgenesis have the same pathoembryological background?

Segmental Spinal Aplasia: Anatomical Variations and Treatment Insights

STUDY DESIGN

Retrospective Cohort Study.

OBJECTIVE

The study aimed to analyze anatomical variants of segmental spinal aplasia (SSA) and investigate factors influencing surgical treatment outcomes, with a specific focus on the incidence of complications.

METHODS

The study focused on patients with SSA treated at a single medical center, with over two years of follow-up. Neurological function changes were evaluated using the modified Japanese Orthopedic Scale (mJOA). Functional independence was measured using the Functional Independence Measure (FIM/WeeFIM) scale, and complications, well-being, and reoperation instances were documented. Statistical analyses used ANOVA and Kruskal-Wallis test.

RESULTS

The predominant localization of SSA in 36 own cases occurs near or at the level of the thoracolumbar junction, often accompanied by significant spinal cord narrowing and a low position of the conus medullaris. Additionally, it frequently presents with aplasia of the lower ribs. Cervicothoracic SSA was more commonly associated with segmentation disorders (P = .04). The most common early complications were wound problems (17%) and neurological deterioration (17%); the most common late complications were: non-fusion (34%); 38% of patients required one or more revision surgery. The type, age of surgery, level of surgery, and initial neurological deficient did not significantly influence the incidence of complications or neurological and functional outcomes.

CONCLUSION

SSA, a range of anomalies appearing early in childhood, progresses gradually. Surgery involves vertebrectomy followed by interbody fusion and screw fixation, guided by neurophysiological monitoring. Surgery is recommended for worsening neurological symptoms, but conservative options like bracing can be considered, due to a high risk of complications.

Association of spinal cord abnormalities with vertebral anomalies: an embryological perspective

PURPOSE

To analyze the relationship between spinal cord and vertebral abnormalities from the point of view of embryology.

METHODS

We analyzed the clinical and radiological data of 260 children with different types of spinal cord malformations in combination with vertebral abnormalities.

RESULTS

Among 260 individuals, approximately 109 presented with open neural tube defects (ONTDs), 83 with split cord malformations (SCMs), and 83 with different types of spinal lipomas. Pathological spina bifida emerged as the most frequent vertebral anomaly, affecting 232 patients, with a higher prevalence in ONTD. Vertebral segmentation disorders, including unsegmented bars, butterfly vertebrae, and hemivertebrae, were present in 124 cases, with a higher prevalence in SCM. The third most common spinal anomaly group consisted of various forms of sacral agenesis (58 cases), notably associated with blunt conus medullaris, spinal lipomas, and sacral myelomeningocele. Segmental aplasia of the spinal cord had a typical association with segmental spinal absence (N = 17).

CONCLUSION

The association between SCM and neuroenteric cyst/canal and vertebral segmentation disorders is strong. High ONTDs often coincide with pathological spina bifida posterior. Type 1 spinal lipomas and focal spinal nondisjunction also correlate with pathologic spina bifida. Segmental spinal absence or dysgenesis involves localized spinal and spinal cord aplasia, sometimes with secondary filar lipoma.

Surgery for spina bifida occulta: spinal lipoma and tethered spinal cord

The technical evolution of the surgery for spina bifida occulta (SBO) over the course of a half-century was reviewed with special foci placed on the spinal lipoma and tethered spinal cord. Looking back through history, SBO had been included in spina bifida (SB). Since the first surgery for spinal lipoma in the mid-nineteenth century, SBO has come to be recognized as an independent pathology in the early twentieth century. A half-century ago, the only option available for SB diagnosis was the plain X-ray, and pioneers of the time persevered in the field of surgery. The classification of spinal lipoma was first described in the early 1970s, and the concept of tethered spinal cord (TSC) was proposed in 1976. Surgical management of spinal lipoma with partial resection was the most widely practiced approach and was indicated only for symptomatic patients. After understanding TSC and tethered cord syndrome (TCS), more aggressive approaches became preferred. A PubMed search suggested that there was a dramatic increase of publications on the topic beginning around 1980. There have been immense academic achievements and technical evolutions since then. From the authors' viewpoint, landmark achievements in this field are listed as follows: (1) establishment of the concept of TSC and the understanding of TCS; (2) unraveling the process of secondary and junctional neurulation; (3) introduction of modern intraoperative neurophysiological mapping and monitoring (IONM) for surgery of spinal lipomas, especially the introduction of bulbocavernosus reflex (BCR) monitoring; (4) introduction of radical resection as a surgical technique; and (5) proposal of a new classification system of spinal lipomas based on embryonic stage. Understanding the embryonic background seems critical because different embryonic stages bring different clinical features and of course different spinal lipomas. Surgical indications and selection of surgical technique should be judged based on the background embryonic stage of the spinal lipoma. As time flows forward, technology continues to advance. Further accumulation of clinical experience and research will open the new horizon in the management of spinal lipomas and other SBO in the next half-century.

Segmental spinal dysgenesis: insights from three consecutive cases and a review of the literature

OBJECTIVE

Segmental spinal dysgenesis (SSD) is a rare congenital spinal abnormality affecting the thoracic and lumbar region of the spine, as well as the spinal cord of neonates and infants. The purpose of the study was to analyze our institution's surgical case series to provide insights into our best practices to contribute to SSD management principles, while conducting a comprehensive literature review.

METHODS

Following institutional review board approval, a retrospective review of SSD surgical cases was examined to observe clinical findings, radiographic findings, management, surgical intervention, and outcomes. Keywords in the comprehensive literature review included SSD, congenital spinal dysgenesis, congenital spinal stenosis, spinal aplasia, and surgery.

RESULTS

Three cases underwent successful surgical management with either improvement or maintenance of neurological baseline. Patients were diagnosed at an average age of 2.7 months, while surgical intervention averaged at 40.3 months with fecal incontinence, neurogenic bladders, spinal cord compression, clubfoot, and concerns for worsening spinal deformity as surgical indicators. The average time for follow-up was 33.7 months and no complications were reported.

CONCLUSIONS

Operative management for SSD is a clinically complex decision that requires multidisciplinary input and care. Patients should be observed at neurological baseline and receive intervention at the appropriate time to allow sufficient growth for functioning without permitting drastic disease progression. Consideration of patient size and spinal instrumentation are significant towards surgical success.

Cervicothoracic dislocation due to congenital and bone-dysplasia-related vertebral malformations

PURPOSE

To evaluate the approaches to treatment of congenital and bone-dysplasia-related pediatric cervicothoracic dislocations and define the optimal treatment method.

METHODS

The publications available in PubMed and Google Scholar data bases were selected following such criteria as the disease in question, pediatric age, the treatment description, and follow-up results. The paper also includes the descriptions of our own six cases of the cervicothoracic dislocations detected in children with different vertebral malformations.

RESULTS

Only eight patients meeting the abovementioned selection criteria were found in the publications: three of them had the Klippel-Feil syndrome (KFS), two had one-level vertebral anomaly, one had neurofibromatosis (NF type 1), one had the Larsen syndrome, and one had a variation of VACTERL association. Their treatment was long term, multi stage, and complicated. Among six our own cases, four patients also had KFS, one had a variation of VACTERL association, and one had NF type 1. All the patients suffered from preoperative neurological disorders. Posterior instrumental fixation with posterior vertebral body resection was performed in four cases and one patient underwent a combined surgery. The parents of one of the patients refused the operation, so he was observed while receiving bracing treatment. Since the treatment was long term and complicated by reoperations, the average follow-up period comprised 5 years.

CONCLUSION

Congenital cervicothoracic dislocations are an extremely rare pathology that manifests itself in early age and requires an early surgical treatment. Failure to provide the treatment leads to the patient's disability. The surgical tactics for such patients is determined individually, but the published data and our own experience demonstrate that early multi-stage combined treatment has been the best option available so far. The cervicothoracic dislocations due to NF 1 manifest later and have a more favorable forecast.

Junctional Neural Tube Defect (JNTD): A Rare and Relatively New Spinal Dysraphic Malformation

Junctional neurulation completes the sequential embryological processes of primary and secondary neurulation as the intermediary step linking the end of primary neurulation and the beginning of secondary neurulation. Its exact molecular process is a matter of ongoing scientific debate. Abnormality of junctional neurulation-junctional neural tube defect (JNTD)-was first described in 2017 based on a series of three patients who displayed a well-formed secondary neural tube, the conus, that is physically separated by a fair distance from its companion primary neural tube and functionally disconnected from rostral corticospinal control. Several other cases conforming to this bizarre neural tube arrangement have since appeared in the literature, reinforcing the validity of this entity. The clinical, neuroimaging, and electrophysiological features of JNTD, as well as the hypothesis of its embryogenetic mechanism, will be described in this chapter.

Severe type of segmental spinal dysgenesis with complete disconnection of the spinal cord and vertebra associated with open neural tube defect

Background

Severe type of segmental spinal dysgenesis (SSD) is a rare and complex anomaly in which the spinal cord completely disconnects at the portion of the spinal dysgenesis. Although closed spinal dysraphisms have been associated with SSD, to the best of our knowledge, the association between open neural tube defect (ONTD) and SSD is significantly rare, with only one case being reported to date.

Case Description

We report a case of an infant with severe SSD and a disconnected spinal cord and spinal column at the thoracolumbar junction associated with myelomeningocele (MMC) in the lumbosacral region. The patient presented severe neurological deficits in the legs and impaired bowel function. The spinal column of L1-L3 was absent. The lower spinal segment consisted of neural placode at the L5-S1 level and no connecting structure between the upper and lower spinal cords. A repair surgery for MMC, including cord untethering and dura plasty, was performed. Histopathological findings revealed a neural placode consisting of a neuroglial tissue and leptomeninges.

Conclusion

The management of severe SSD during the perinatal period is more challenging when it is associated with ONTD. We report detailed neuroradiological, intraoperative, and histological findings of such a case and discuss the embryopathogenesis of the associated ONTD and the treatment strategies.

Disorders of Secondary Neurulation: Suggestion of a New Classification According to Pathoembryogenesis

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.

Junctional Neurulation : A Junction between Primary and Secondary Neural Tubes

Recent case reports of junctional neural tube defect (JNTD) which is a peculiar type of spinal anomaly showing the functional disconnection of the primary and secondary neural tubes has risen interest in the process of junctional neurulation (the connection between the two neural tubes) during development. This article summarizes the clinical features of the JNTD and reviews the literature on the basic research on junctional neurulation.

Disorders of Secondary Neurulation : Mainly Focused on Pathoembryogenesis

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.

Surgical treatment of segmental spinal dysgenesis: a report of 19 cases

STUDY DESIGN

Retrospective review.

OBJECTIVE

To describe clinical presentation, surgical management, long-term results, and complications in patients with segmental spinal dysgenesis (SSD). In addition, we sought to emphasize early surgery for this complex congenital abnormality. SSD is a rare congenital malformation characterized by focal stenosis, spinal subluxation, kyphosis, and absence of the nerve roots. Neurologic function ranges from normal to complete paraplegia. Progression of the deformity and neurologic deterioration is the rule.

METHODS

An independent spinal surgeon reviewed the complete records of 19 patients with SSD, between 1998 and 2015 at a single institution. Mean follow-up was 10 years and 6 months (2-14 years).

RESULTS

We evaluated 11 males and 8 females, with a mean age of 2 years and 9 months (5 months-15 years). The dysgenetic segment involved an average of 2.9 vertebrae (1-5); the upper thoracic region was most commonly involved in ten cases. Fifteen patients had severe spinal stenosis. 14 patients presented neurological deficits and 15 patients had associated organ and musculoskeletal anomalies.Twenty-seven surgeries were performed, a mean of 1.76 procedures (1-5) to obtain solid fusion. Neurologic function improved in four, deteriorated in three, and remained unchanged in 12 patients Seven complications were recorded.

CONCLUSION

We strongly recommend decompression and fusion as soon as possible to preserve or prevent neurologic deterioration. Although challenging, it was possible to achieve a solid instrumented fusion in all cases; however, a high rate of patients may deteriorate or not recover neurological status after surgery.

LEVEL OF EVIDENCE

Level IV evidence.

Spinal Dysraphism in the Last Two Decades : What I Have Seen during the Era of Dynamic Advancement

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 amidst the period. I review here the last two decades from my personal point of view on what has been achieved in the field of spinal dysraphism, focusing on occult tethered cord syndrome, lumbosacral lipomatous malformation, terminal myelocystocele, retained medullary cord, limited dorsal myeloschisis and junctional neural tube defect. There are still many issues to revise, add and extend. Profound knowledge of basic science is critical, as well as refined clinical analysis. I expect that young scholars who follow the footsteps of precedent giants will shed bright light on this topic in the future.

Junctional Neural Tube Defect

Junctional neurulation represents the most recent adjunct to the well-known sequential embryological processes of primary and secondary neurulation. While its exact molecular processes, occurring at the end of primary and the beginning of secondary neurulation, are still being actively investigated, its pathological counterpart -junctional neural tube defect (JNTD)- had been described in 2017 based on three patients whose well-formed secondary neural tube, the conus, is widely separated from its corresponding primary neural tube and functionally disconnected from corticospinal control from above. Several other cases conforming to this bizarre neural tube arrangement have since appeared in the literature, reinforcing the validity of this entity. The cardinal clinical, neuroimaging, and electrophysiological features of JNTD, and the hypothesis of its embryogenetic mechanism, form part of this review.