A case of junctional neural tube defect associated with a lipoma of the filum terminale: a new subtype of junctional neural tube defect?

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.

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.

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.

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

INTRODUCTION

Junctional neural tube defect (JNTD) is a recently introduced form of congenital spinal dysraphism that is characterized by functional disconnection between the primary and secondary neural tubes. The upper and lower cords appeared to be connected by a non-functioning band-like structure. JNTD is suspected to arise from a developmental error not corresponding to either primary or secondary neurulation, but rather between the two neurulation processes. On the other hand, segmental spinal dysgenesis (SSD) is an older entity of spinal anomalies in which a segment of the spine and spinal cord does not develop properly. The anomaly had been noted for the bony abnormality, as it is the most prominent feature. Based on the recent encounter of two cases resembling both entities, we sought the possibility that the two diseases may have the same pathoembryogenesis.

METHODS AND RESULTS

Based on the impression that the two entities share important features, we compared the details of the two anomalies. First, our two recently encountered cases of JNTD were described. Second, previous reports of SSD were comprehensively reviewed. The two cases had the essential anomaly of the neural structures satisfying the definition of JNTD, as well as the elaborate spinal deformity as seen in SSD. In the previous literature on SSD, it was recognized that in addition to the bone anomaly, disconnected spinal cord was present. Hence, the two entities seem to have many similar clinical and neuroimaging features. The dysgenic spinal level is similar, and the disconnection between the primary and secondary neural tubes is found in the two diseases. The two neural tubes are connected by a band-like structure, with severe stenosis of the spinal canal at the level of the band. Both entities show segmental anomalies of the vertebrae in the thoracolumbar region, especially in the posterior element. Although the extent of shared features seems high, the previously suggested hypothetical pathoembryogenesis of SSD did not involve the process of junctional neurulation. We suggest that SSD shares the same origin as JNTD, and the bony abnormality may be a secondary phenomenon to the core error during neural tube development.

CONCLUSIONS

We propose that JNTD and SSD may be the same entity, originating from an error during junctional neurulation. As there is controversy regarding the treatment strategy for both entities, unified accumulation of clinical experience and analysis may help improve the management of patients.