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Limited dorsal myeloschisis involving one hemicord of a split cord malformation — a “hemi-LDM”

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Dachling Pang
Dachling Pang
Dachling Pang
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Abel Devadass
Abel Devadass
Abel Devadass
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Dominic Thompson
Dominic Thompson
Dominic Thompson
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Abstract and Figures

This is a case report of an exceedingly rare case of a limited dorsal myeloschisis (LDM) with its stalk inserted on the midline dorsal surface of one of a pair of hemicords in a type II split cord malformation. This entity, literally a “hemi-LDM,” has been seen only once by the senior author in his catalogue of over 200 cases of LDM (Pang et al., 2020), nor has it been reported elsewhere before. We postulate that here the mechanism of focal nondisjunction of the hemi-neural plate during primary neurulation, which produces LDMs, occurs at the cusp of the consecutive developmental stages of gastrulation and primary neurulation, right after the appearance of the hemi-neural plates and hemi-notochords caused by the endomesenchymal tract. This child also had a terminal lipoma attached to the end of the conus, indicating that disruption of all three tandem stages of neural tube formation, namely, gastrulation, primary neurulation, and secondary neurulation, can occur in the same individual.
Typical cutaneous signature of a non-saccular LDM, consisting of a shiny, non-full thickness skin crater surrounded by heaped up skin crested by a melanin-laden patch on top
Typical cutaneous signature of a non-saccular LDM, consisting of a shiny, non-full thickness skin crater surrounded by heaped up skin crested by a melanin-laden patch on top
… 
MRI of the composite lesions. Left: axial T2 images show the type II SCM, a gastrulation defect, at 2 levels. The merge point of the LDM stalk with the left hemicord is not apparent. Middle: T2 sagittal image showing the LDM stalk, a primary neurulation defect, tracking from the skin crater caudally to enter the spinal canal through the L4–L5 interlaminar space. Right: T1 sagittal and axial images show a terminal lipoma, a pure secondary neurulation defect
MRI of the composite lesions. Left: axial T2 images show the type II SCM, a gastrulation defect, at 2 levels. The merge point of the LDM stalk with the left hemicord is not apparent. Middle: T2 sagittal image showing the LDM stalk, a primary neurulation defect, tracking from the skin crater caudally to enter the spinal canal through the L4–L5 interlaminar space. Right: T1 sagittal and axial images show a terminal lipoma, a pure secondary neurulation defect
… 
Intraoperative picture shows the skin crater excised via an elliptical incision, the underlying extradural LDM stalk, and the intradural LDM stalk through the still intact arachnoid, coursing rostrally towards the merge point (not exposed). The rostral spinal cord is on the right
Intraoperative picture shows the skin crater excised via an elliptical incision, the underlying extradural LDM stalk, and the intradural LDM stalk through the still intact arachnoid, coursing rostrally towards the merge point (not exposed). The rostral spinal cord is on the right
… 
Intraoperative picture shows the LDM stalk inserts on to a nubbin that looks and feels neural in texture, on the dorsal midline of the left hemicord. The thin fibrous septum issuing from the median cleft of the split cord is attached to the medial surface of each hemicord, and is also partially adherent to the LDM stalk and partially to the dura
Intraoperative picture shows the LDM stalk inserts on to a nubbin that looks and feels neural in texture, on the dorsal midline of the left hemicord. The thin fibrous septum issuing from the median cleft of the split cord is attached to the medial surface of each hemicord, and is also partially adherent to the LDM stalk and partially to the dura
… 
Intraoperative end-on view after resection of the median fibrous septum of the SCM and revealing of the median cleft, shows clearly the location of the merge point of the LDM stalk with its protruding neural nubbin on the dorsal midpoint of the left hemicord, just rostral to the caudal reunion site of the two hemicords. The right hemicord looks entirely normal
+7
Intraoperative end-on view after resection of the median fibrous septum of the SCM and revealing of the median cleft, shows clearly the location of the merge point of the LDM stalk with its protruding neural nubbin on the dorsal midpoint of the left hemicord, just rostral to the caudal reunion site of the two hemicords. The right hemicord looks entirely normal
… 
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https://doi.org/10.1007/s00381-022-05599-0
CASE REPORT
Limited dorsal myeloschisis involving one hemicord ofasplit cord
malformation — a“hemi‑LDM”
DachlingPang1,2 · AbelDevadass1· DominicThompson1
Received: 5 April 2022 / Accepted: 1 July 2022
© The Author(s), under exclusive licence to Springer-Verlag GmbH Germany, part of Springer Nature 2022
Abstract
This is a case report of an exceedingly rare case of a limited dorsal myeloschisis (LDM) with its stalk inserted on the mid-
line dorsal surface of one of a pair of hemicords in a type II split cord malformation. This entity, literally a “hemi-LDM,”
has been seen only once by the senior author in his catalogue of over 200 cases of LDM (Pang etal., 2020), nor has it been
reported elsewhere before. We postulate that here the mechanism of focal nondisjunction of the hemi-neural plate during
primary neurulation, which produces LDMs, occurs at the cusp of the consecutive developmental stages of gastrulation and
primary neurulation, right after the appearance of the hemi-neural plates and hemi-notochords caused by the endomesen-
chymal tract. This child also had a terminal lipoma attached to the end of the conus, indicating that disruption of all three
tandem stages of neural tube formation, namely, gastrulation, primary neurulation, and secondary neurulation, can occur
in the same individual.
Keywords Composite malformation· Embryogenetic mechanism· Gastrulation· Focal incomplete disjunction· Limited
dorsal myeloschisis· Primary neurulation· Split cord malformation
Introduction
Split cord malformation (SCM) and limited dorsal mye-
loschisis (LDM) are both uncommon spinal dysraphic
malformations, the former more so than the latter since
improved knowledge of the embryogenesis and heightened
awareness of the characteristic skin signatures of LDM over
the past decade have somewhat escalated LDM to popu-
lar platforms in paediatric neurosurgery seminars and as
favourite subjects in professional journals. There is now
strong evidence that the embryogeneses of SCM and LDM
involve distinct though consecutive stages of neural tube
development: SCM represents a defect of gastrulation when
the shuffling of epiblastic cells from the unilaminar blastula
converts it into a trilaminar gastrula, following which proto-
notochordal cells migrate from each side of the dorsal lips of
the primitive pit at the avian Hensen’s node (primitive knot
in human) to insinuate themselves between the newly formed
ectoderm-endoderm layers through the important process of
midline integration [1–3]. Failure of midline integration of
these proto-notochordal cells probably permits a focal spot
where the ectoderm and endoderm remain tightly adherent,
resulting in formation of a midline ecto-endodermal tract
around which all the features of split spinal cord evolve [2].
Limited dorsal myeloschisis is thought to be a defect in the
next consecutive stage after gastrulation, that of primary
neurulation, when the neural plate folds up dorsally with the
surface ectoderm still attached to its two “shoulders” (the
neural folds), which ultimately undergo dorsal fusion in the
midline to complete the shape of the primary neural tube.
LDM probably results from a focal non-fusion of the con-
joint surface and neural ectoderms, and consequent nondis-
junction of the one ectoderm from the other so that a physi-
cal link, or stalk, often containing neural or meningothelial
tissue, remains, connecting the base of the future skin to the
dorsal midline of the otherwise completely formed spinal
cord [4–7].
Because SCM and LDM are defects of distinct stages of
neural tube development, when they occur together, and we
have encountered many examples of such, they invariably
* Dachling Pang
PangTV@aol.com
1 Department ofPaediatric Neurosurgery, Great Ormond
Street Hospital forChildren NHS Trust, Great Ormond
Street, LondonWC1N3JH, UK
2 Paediatric Neurosurgery, University ofCalifornia, Davis,
USA
/ Published online: 6 July 2022
Child's Nervous System (2022) 38:2223–2230
Content courtesy of Springer Nature, terms of use apply. Rights reserved.
Gastrulation and Split Cord Malformation
Chapter
  • Aug 2023
  • Adv Tech Stand Neurosurg
Split cord malformation (SCM) is a rare form of closed spinal dysraphism, in which two hemi-cords are present, instead of a single spinal cord. SCM is categorised into type 1 and type 2. Type 1 SCM is defined by the presence of a bony or osseocartilaginous spur between the hemi-cords, whereas type 2 SCM has no bony spur, and the two hemi-cords are contained within a single dura. In this chapter, we present the putative mechanisms by which SCM arises, including gastrulation defects and Pang’s unified theory. The typical and rare clinical presentations and variations are described. Finally, we outline the step-by-step surgical approach to both SCM 1 and 2 and the overall prognosis of both conditions.KeywordsSplit cord malformationGastrulationEndodermMesodermEctodermNotochordTetheringProphylactic surgery
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Focal Spinal Nondisjunctional Disorders: Including a Discussion on the Embryogenesis of Cranial Focal Nondisjunctional Lesions
Chapter
  • Aug 2023
  • Adv Tech Stand Neurosurg
The publication of a comprehensive report on limited dorsal myeloschisis by the senior author (DP) in 2010 has brought full attention to the concept of limited myeloschisis that he first formulated in 1992 and ignited interests in the whole spectrum of focal spinal nondisjunctional disorders. Now that focal nondisjunctional disorders have become well known, new clinical reports on these conditions or relevant subjects are frequently seen. Here we present an updated review on the full spectrum of focal spinal nondisjunctional disorders and extend the scope to include a discussion on the embryogenesis of cranial focal nondisjunctional malformations.KeywordsLimited dorsal myeloschisisDermal sinus tractDermoidNondisjunctionDysraphismFocal spinal nondisjunctional disordersFocal cranial nondisjunctional disordersEncephalocele
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Focal Spinal Nondisjunction in Primary Neurulation : Limited Dorsal Myeloschisis and Congenital Spinal Dermal Sinus Tract
Article
Full-text available
  • Mar 2021
Spinal dysraphic lesions due to focal nondisjunction in primary neurulation are commonly encountered in paediatric neurosurgery, but the "fog-of-war" on these conditions was only gradually dispersed in the past 10 years by the works of the groups led by the senior author and Prof. Kyu-Chang Wang. It is now clear that limited dorsal myeloschisis and congenital spinal dermal sinus tract are conditions at the two ends of a spectrum; and mixed lesions of them with various configurations exist. This review article summarizes the current understanding of these conditions' embryogenetic mechanisms, pathological anatomy and clinical manifestations, and their management strategy and surgical techniques.
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Surgical management of complex spinal cord lipomas: how, why, and when to operate. A review
Article
  • May 2019
This review summarizes the classification, anatomy, and embryogenesis of complex spinal cord lipomas, and it describes in some detail the new technique of total lipoma resection and radical reconstruction of the affected neural placode. Its specific mission is to tackle two main issues surrounding the management of complex dysraphic lipomas: whether total resection confers better long-term benefits than partial resection and whether total resection fares better than conservative treatment—i.e., no surgery—for asymptomatic lipomas. Accordingly, the 24-year progression-free survival data of the author and colleagues’ series of over 300 cases of total resection are compared with historical data from multiple series (including the author and colleagues’ own) of partial resection, and total resection data specifically for asymptomatic lesions are compared with the two known series of nonsurgical treatment of equivalent numbers of patients. These comparisons amply support the author’s recommendation of total resection for most complex lipomas, with or without symptoms. The notable exception is the asymptomatic chaotic lipoma, whose peculiar anatomical relationship with the neural tissue defies even this aggressive surgical approach and consequently projects worse results (admittedly of a small number of cases) than for the other two lipoma subtypes of dorsal and transitional lesions. Prophylactic resection of asymptomatic chaotic lipomas is therefore not currently endorsed.
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Limited Dorsal Myeloschisis: Reconsideration of its Embryological Origin
Article
  • Jan 2019
  • NEUROSURGERY
Background: Limited dorsal myeloschisis (LDM) is postulated to be a result of incomplete dysjunction in primary neurulation. However, clinical experience of LDM located below the first-second sacral (S1-S2) vertebral level, which is formed from secondary neurulation (S2-coccyx), suggested that LDM may not be entirely explained as an error of primary neurulation. Objective: To elucidate the location and characteristics of LDM to investigate the possible relation of its pathoembryogenesis to secondary neurulation. Methods: Twenty-eight patients were surgically treated for LDM from 2010 to 2015. Since the level where the LDM stalk penetrates the interspinous ligament is most clearly defined on the preoperative MRI and operative field, this level was assessed to find out whether the lesions can occur in the region of secondary neurulation. Results: Eleven patients (39%) with typical morphology of the stalk had interspinous defect levels lower than S1-S2. These patients were not different from 17 patients with classic LDMs at a level above or at S1-S2. This result shows that other than the low level of the interspinous level, 11 patients had lesions that could be defined as LDMs. Conclusion: By elucidating the location of LDM lesions (in particular, the interspinous level), we propose that LDM may be caused by errors of secondary neurulation. The hypothesis seems more plausible due to the supportive fact that the process of separation between the cutaneous and neural ectoderm is present during secondary neurulation. Hence, incomplete disjunction of the two ectoderms during secondary neurulation may result in LDM, similar to the pathomechanism proposed during primary neurulation.
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Classification of Spinal Dysraphic Malformations According to Embryogenesis: Gastrulation Defects and Split Cord Malformation
Chapter
  • Jun 2017
It is not birth, marriage, or death, but gastrulation which is truly the important event in your life (Wolpert 2008)
View
Modification of surgical procedure for “probable” limited dorsal myeloschisis
Article
  • Feb 2017
OBJECTIVE Since the entity limited dorsal myeloschisis (LDM) was proposed, numerous confusing clinical cases have been renamed according to the embryopathogenesis. However, clinical application of this label appears to require some clarification with regard to pathology. There have been cases in which all criteria for the diagnosis of LDM were met except for the presence of a neural component in the stalk, an entity the authors call “probable” LDM. The present study was performed to meticulously review these cases and suggest that a modified surgical strategy using limited laminectomy is sufficient to achieve the surgical goal of untethering. METHODS The authors retrospectively reviewed the imaging findings, operative notes, and pathology reports of spinal dysraphism patients with subcutaneous stalk lesions who had presented to their institution between 2010 and 2014. RESULTS Among 33 patients with LDM, 13 had the typical nonsaccular lesions with simple subcutaneous stalks connecting the skin opening to the spinal cord. Four cases had “true” LDM meeting all criteria for diagnosis, including pathological confirmation of CNS tissue by immunohistochemical staining with glial fibrillary acidic protein. There were also 9 cases in which all clinical, imaging, and surgical findings were compatible with LDM, but the “neural” component in the resected stalk was not confirmed. For all the cases, limited exposure of the stalk was done and satisfactory untethering was achieved. CONCLUSIONS One can speculate based on the initial error of embryogenesis that if the entire stalk were traced to the point of insertion on the cord, the neural component would be proven. However, this would require an extended level of laminectomy/laminotomy, which may be unnecessary, at least with regard to the completeness of untethering. Therefore, the authors propose that for some selected cases of LDM, a minimal extent of laminectomy may suffice for untethering, although it may be insufficient for diagnosing a true LDM.
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Split Cord Malformation
Article
  • Sep 1992
THIRTY-NINE PATIENTS with split cord malformations (SCM) were studied in detail with respect to their clinical, radiographic, and surgical findings as well as their outcome data. Eight patients were adults and 31 patients were children. According to the classification endorsed by Part I of the SCM study, 19 patients had Type I SCM (6 adults and 13 children), 18 patients had Type II SCM (2 adults and 16 children), and 2 patients had composite SCM with both lesion types situated in tandem. Six SCMs were cervical, 2 were thoracic, and 31 were in the lumbar region. All 8 adults had pain and progressive sensorimotor deficits at diagnosis. Only 16 of the 31 children had symptoms, and among these, 14 had progressive sensorimotor deficits, but only 6 had pain. The difference in the clinical picture between adults and children is similar to that described in the tethered cord syndrome, except for left-right functional discrepancy, which was prominent in 8 children with SCM but rarely seen in tethered cord syndrome due to other causes. Cutaneous manifestations of either occult or open dysraphic states were present in all but 3 patients; hypertrichosis was by far the best predictor of an underlying SCM, being found in 56% in the series. Neurological deterioration in SCM was independent of the lesion type: the Type I:Type II ratio for symptomatic progression was 13:11. It was also independent of the location of the lesion: 67% of patients with cervical SCMs had symptomatic progression versus 64% of patients with thoracolumbar lesions. High-resolution, thin cut, axial computed tomographic myelography using bone algorithms was more sensitive than magnetic resonance imaging in defining the anatomical details of the SCM. Radiographic classifications of the SCM, using the nature of the median septum and the number of dural tubes as criteria, was always possible without ambiguity. However, whereas every Type I bone septum was identified preoperatively, only 5 Type II fibrous septa were revealed by preoperative imaging, even though a fibrous septum and/or other fibroneurovascular bands were found tethering the hemicords in every Type II case at surgery. Complete imaging studies also showed that all lumbar SCMs had low-lying coni and at least one additional tethering lesion besides the split cords, whereas only 1 of 7 cervical and high thoracic SCMs had a low conus and a second tethering lesion. The surgical goal for SCM was release of the tethered hemicords by eliminating the bone spurs, dural sleeves, fibrous septa, or any fibroneurovascular bands (myelomeningoceles manqué) that might be transfixing the split cord. Type I cases were technically more difficult and had a slightly higher surgical morbidity than Type II cases, especially if an oblique bone septum had asymmetrically divided the cord into one larger hemicord and one smaller, hence, very delicate, hemicord. Overall, 89% of patients surgically treated experienced either improvement or stabilization of their preoperative neurological status. Thus, this study strongly argues that both types of SCM are cord tethering lesions likely to cause neurological damage, and both should be treated. All Type II SCMs should be explored, even if a definite median septum was not revealed by imaging studies. The entire neuraxis should be studied to look for other tethering lesions, which should also be treated. Surgery is excellent for improving or stabilizing the neurological status.
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Surgical treatment of complex spinal cord lipomas
Article
  • Sep 2013
  • CHILD NERV SYST
This paper shows the long-term benefits of total/near-total resection of complex spinal cord lipomas and meticulous reconstruction of the neural placode, and specifically, its advantage over partial resection, and over non-surgical treatment for the subset of children with asymptomatic virgin lipomas. The technique of total resection and placode reconstruction, together with technical nuances, are described in detail. We added 77 patients with complex lipomas to our original lipoma series published in 2009 and 2010, to a total of 315 patients who had had total or near-total resection and followed for a span of 20 years. Long-term outcome is measured by overall progression-free survival (PFS) with the Kaplan-Meier analysis, and by subgroup Cox proportional recurrence hazard analysis for the influence on outcome of 4 predictor variables of lipoma type, presence of symptoms, prior surgery, and post-operative cord-sac ratio. These results are compared to an age-matched, lesion-matched series of 116 patients who underwent partial lipoma resection over 11 years. The results for total resection is also compared to two large published series of asymptomatic lipomas followed without surgery over 9 to 10 years, to determine whether prophylactic total resection confers better long-term protection over conservative treatment for children with asymptomatic lipomas.. The PFS after total resection for all lipoma types and clinical subgroups is 88.1 % over 20 years versus 34.6 % for partial resection at 10.5 years (p < 0.0001). Culling only the asymptomatic patients with virgin (previously unoperated) lipomas, the PFS for prophylactic total resection for this subgroup rose to 98.8 % over 20 years, versus 67 % at 9 years for one group of non-surgical treatment and 60 % at 10 years for another group of conservative treatment. Our own as well as other published results of partial resection also compare poorly to non-surgical treatment for the subset of asymptomatic virgin lipomas. Multivariate subgroup analyses show that cord-sac ratio is the only independent variable that predicts outcome, with a 96.9 % PFS for ratio <30 % (loosest sac), 86.2 % for ratio between 30 and 50 %, and 78.3 % for ratio >50 % (tightest sac), and a threefold increase in recurrence hazard for high ratios (p = 0.0009). Pre-operative patient profiling using multiple correspondence analysis shows the ideal patient for total resection is a child less than 2 years old with a virgin asymptomatic lipoma, who, with a PFS of 99.2 %, is virtually cured by total resection. Total/near-total resection of complex lipomas and complete reconstruction of the neural placode achieves far better long-term protection against symptomatic recurrence than partial resection for all lesions; and for the subset of asymptomatic virgin lipomas, also better than non-surgical treatment. Partial resection in many cases produces worse outcome than conservative treatment for asymptomatic lesions.
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