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Purpose: The presence and progression of symptoms is the basis for deciding to perform surgery in infants with closed spinal dysraphism (CSD); however, identifying symptoms could be limited, making it difficult to decide. This study investigated whether an electrodiagnostic study (EDS) can provide evidence of neural damage in asymptomatic infants with CSD., Methods: The study group comprised infants with CSD suspected of having neural damage based on structural abnormalities in spinal ultrasound findings. The patients' medical records were reviewed retrospectively for their clinical presentation, neuroimaging findings, urodynamic study (UDS) results, EDS findings, and surgical status., Results: Among 125 infants who underwent EDS and UDS, 117 (94%) had no clinical symptoms, except for cutaneous manifestations. Among these asymptomatic patients, 51 individuals (43.6%) had abnormal EDS findings; 33 subjects (28.2%) showed abnormal findings on EDS alone, while 37 (31.6%) on UDS alone, and 18 (15.4%) on both EDS and UDS. Chi-square test showed an opposite relationship between the two test results; when EDS was abnormal, UDS was often normal and vice versa (χ 2  = 5.328, p = 0.021). In all cases with abnormal EDS, denervation potentials, such as fibrillation and positive sharp waves, were observed on needle electromyography. However, abnormal findings in the nerve conduction study were observed only in six cases., Conclusion: Subclinical neural damage was identified through EDS in asymptomatic infants with CSD. EDS could be necessary to determine whether follow-up monitoring only or surgical intervention is required for this patient group complementing UDS findings., (© 2022. The Author(s), under exclusive licence to Springer-Verlag GmbH Germany, part of Springer Nature.)

Purpose: Retethering of the cord can occur after the initial untethering surgery. Typical neurological manifestations indicative of cord tethering are often difficult to determine in pediatric patients. Patients who had a primary untethering operation are likely to present with some degree of neurological deficits from a previous tethering event, and urodynamic studies (UDSs) and spine images are frequently abnormal. Therefore, more objective tools to detect retethering are needed. This study sought to delineate the characteristics of EDS of retethering, and therefore, could support the diagnosis of retethering., Methods: Among 692 subjects who had an untethering operation, data from 93 subjects who had been suspected of retethering clinically were retrospectively extracted. The subjects were divided into two groups, a retethered group, and a non-progression group, according to whether or not surgical interventions had been performed. Two consecutive EDSs, clinical findings, spine magnetic resonance imaging scans, and UDSs before the development of new tethering symptoms were reviewed and compared., Results: In the electromyography (EMG) study, the appearance of abnormal spontaneous activity (ASA) in new muscles was prominent in the retethered group (p < 0.01). The loss of ASA was more pronounced in the non-progression group (p < 0.01). Specificity and sensitivity of EMG for retethering were 80.4 and 56.5%, respectively. In the nerve conduction study, the two groups did not show differences. The size of fibrillation potential was not different between the groups., Conclusions: To provide support for a clinician's decision on retethering, EDS could be an advantageous tool with high specificity when the results are compared to previous EDS results. Routine follow-up EDS post-operatively is recommended as a baseline for comparison at the time when retethering is clinically suspected., (© 2023. The Author(s), under exclusive licence to Springer-Verlag GmbH Austria, part of Springer Nature.)

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., (© 2021. The Author(s), under exclusive licence to Springer-Verlag GmbH Germany, part of Springer Nature.)

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., (© 2022. The Author(s), under exclusive license to Springer Nature Switzerland AG.)

Introduction: Retained medullary cord (RMC) is thought to be a product of arrested secondary neurulation during the regression phase. A cord-like structure with a caudal non-functional part ends at the cul-de-sac. If the arrest occurs at the cavitation phase of secondary neurulation, the medullary cord has a cystic portion making "RMC of cystic type.", Clinical Presentation: We report a case of a 4-month-old girl who had a low-lying conus with an extradural-looking dorsal cyst. Preoperative diagnosis was RMC with a lumbosacral extradural cyst such as an arachnoid cyst. At surgery, we found that the extradural cyst was an extension of dural sac with the caudal portion of the cystic RMC inside. The RMC was untethered and the dural sac was reconstructed. The histopathologic examination revealed findings compatible with cystic RMC attached to the cul-de-sac., Conclusions: We regard this case as an intermediate form between the typical RMC in which is regarded as regression arrest occurred after the terminal balloon collapsed and the medullary cord detached from the skin to the normal cul-de-sac, and the terminal myelocystocele which is considered the result of arrest at the phase of the persisted terminal balloon attached to the skin.

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.