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151
Copyright © 2021 The Korean Neurosurgical Society
Review Article
J Korean Neurosurg Soc 64 (2) : 151-188, 2021
https://doi.org/10.3340/jkns.2020.0117 pISSN 2005-3711 eISSN 1598-7876
Focal Spinal Nondisjunction in Primary Neurulation :
Limited Dorsal Myeloschisis and Congenital Spinal
Dermal Sinus Tract
Sui-To Wong,1 Dachling Pang2,3
Department of Neurosurgery,
1
Tuen Mun Hospital, Hong Kong, Hong Kong
Department of Paediatric Neurosurgery,
2
Universit y of California, Davis, CA, USA
Department of Paediatric Neurosurgery,
3
Great Ormond Street Hospital for Children, NHS Trust, London, UK
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 congurations 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.
Key Words : Limited dorsal myeloschisis · Spinal dermal sinus tract · Dermoid · Nondisjunction · Dysraphism · Focal spinal
nondisjunctional disorders.
• Received : April 21, 2020 • Revised : July 29, 2020 • Accepted : July 29, 2020
• Address for reprints : Dachling Pang
Department of Paediatric Neurosurgery, Great Ormond Street Hospital for Children, NHS Trust, Great Ormond Street, London WC1N3JH, UK
Tel : +44-20-7405-9200, Fax : +44-20-7813-8279, E-mail : pangtv@aol.com, ORCID : https://orcid.org/0000-0002-6603-6546
This is an Open Access ar ticle distributed under the terms of the Creative Commons Attribution Non-Commercial License (http://creativecommons.org/ licenses /by-nc/4.0)
which permits unrestricted non-commercial use, distribution, and reproduction in any medium, provided the original work is properly cited.
INTRODUCTION
Focal nondisjunction of the primary neural tube in its spi-
nal cord region results in a normal or near-normal spinal
cord, except for the presence of a tract anchoring the dorsal
surface of the spinal cord to the base of a characteristic skin
lesion. This tract, depending on its cellular constituents and
its completeness in extent, can lead to tethered cord syndrome
and/or collection of dermal sinus tissue with their dreadful ef-
fects. This review aims to give a concise and updated summa-
ry of the conditions that have been grouped under a common
embryogenetic mechanism, including congenital spinal der-
mal sinus tract (CSDST), limited dorsal myeloschisis (LDM),
and their mixed lesions3,5,6,11,25,39,42). A comprehensive study on
these focal spinal nondisjunctional disorders (FSNDs) can be
found in a recent book chapter titled “Limited dorsal spinal
nondisjunctional disorders”
43).
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EMBRYOGENETIC MECHANISMS
The basis for grouping these conditions as one
entity
Primary neurulation can be broadly divided into four main
stages, occurring sequentially at each axial level of the embryo,
during that the neural plate goes through 1) formation, 2)
shaping, 3) dorsal bending, and 4) closure of the neural groove
to become the primar y neural tube2). At the tissue level, the
last stage actually consists of a complex sequence of three
overlapping events2 ,14, 31,41) (Fig. 1) : 1) A broad overlapping sur-
face epithelium (SE) and neuroepithelium (NE) junction of
several cells’ thickness is formed at the paired neural folds. It
occurs as the neural folds progressively elevate and converge
towards the dorsal midline, and the NE cells enlarge in height
and drag the flattened SE cells onto their dorsal surface.
2) The two overlapping epithelia through progressive delami-
nation become completely separate, known as disjunction.
The delamination process starts with an inter-epithelial space
in the middle part of the interface of the two epithelia. As the
space expands, it acquires a crescent shape because the basal
lamina of the two epithelia remains attached at the ventro-lat-
eral extreme of their contact (ventral contact point). While the
two neural folds are progressively approaching each other to
close the dorsal midline gap, the inter-epithelial space extends
further dorsally towards the dorsal midline. Ventrally, the
basal lamina bridge at the ventral contact point finally breaks
down, and the two epithelia separate there. A new basal lami-
na then forms on the “inter-epithelial surfaces” of each of the
two epithelia. When the inter-epithelial space on each side
reaches the dorsal-most meeting point of the two epithelia and
separates them, it consummates disjunction. 3) During the
same period, fusion of the two epithelial layers at the dorsal
midline occurs. Fusion is preceded by apposition of the two
opposing sets of epithelia at the tips of the two neural folds,
and formation of intercellular adhesion at contact points,
Fig. 1.
Normal primar y neurulation. Diagrams showing the major steps in closure of the neural groove in an axial level. A : Elevation of the neural folds
(arrow). B : Progressive elevation of the neural folds. Delamination at the neuroepithelium – surface epithelium interface. C : Components involved in
the nal phase in closure of the neural groove. D : Closed neural tube at an axial level. Reused from Wong et al.
43)
with permission from Springer Nature.
SE : surface epithelium, NE : neuroepithelium, n : notochord, en : endoderm.
A
C
B
D
SE
SE
Fusion of SE
Fusion of NE
site of disjunction
Inter-epithelial space
SE
SE
NE
NE
NE
NE
n
n
n
en
en
en
Focal Spinal Nondisjunction | Wong ST, et al.
153
J Korean Neurosurg Soc 64 (2) : 151-188
which are initially discontinuous from superficial to deep33).
In normal embryos, completion of neural groove closure at an
axial level is marked by the appearance of a continuous basal
lamina under the SE across the dorsal midline, and a continu-
ous sheath of basal lamina around the NE (primary neural
tube) at that level15). There are two subtle details of these inter-
calated processes that are important to our embryogenetic hy-
potheses : first, fusion of the two epithelial layers likely pro-
ceeds independently of each other41). Secondly, although the
exact timing of epithelial fusion and disjunction is unknown,
intuitively, fusion of the epithelia must precede disjunction of
the SE and NE.
Faults occurring at a focal point during these last phases of
neural groove closure give rise to FSNDs, which are character-
ized by nondisjunction and incomplete fusion of a focal, or
“limited”, segment anywhere along the future spinal cord
down to the S1 or S2 cord level9,18 ,19,27). Depending on the aber-
rant behaviours of the various primordial cells involved in the
neural groove closure, several anatomical phenotypes of the
final malformation are seen. In addition, the matured features
of the subtype malformations of FSND are determined by in-
dividual or combined errors of the primordial SE and NE
cells, as well as the mesoderm and neural crest cells (Fig.
2)31,32,37).
At the molecular genetic level, the mechanisms of primary
neurulation have only been partially elucidated. The different
stages of primary neurulation have different key molecular
players2 0). In FSNDs, the underlying faulty molecular events
are likely confined to those related to fusion of the epithelia
and delamination/disjunction occurring at the dorsal midline.
One group of regulator proteins that may be targets in the
genesis of FSND are the Rho GTPases, including Rac1 and
Cdc42. Both Rac1 and Cdc42 are involved in the regulation of
cellular protrusions in SE during dorsal midline fusion20 ,28). As
for the molecular mechanisms of nondisjunction, there is even
scarcer information; one possibly point of aberration may oc-
cur during the caspase-dependent apoptosis of the cells at the
SE-NE border20, 44). There are two general points about defec-
tive molecular mechanisms in FSNDs : 1) to account for the
“limited” extent of a FSND lesion, a causative molecular de-
Fig. 2.
Proposed embryogenetic mechanisms for different types of focal spinal non-disjunctional disorders. A : Congenital spinal dermal sinus tract
(CSDST). B : Limited dorsal myeloschisis (LDM). C : Mixed CSDST and LDM –
“
orthodox
”
type and
“
conjoint
”
type. D : LDM with hidden dermal elements.
SE : surface epithelium, NE : neuroepithelium.
A
C
B
D
SE
SE
SE
SE cells
SE
Dermal sinus tract
Mixed CSDST & LDM LDM tract with
hidden dermal elements
LDM tract
Failed fusion of SE
Failed fusion of SE
Failed fusion of NE
“Orthodox” tract “Conjoint” tract
Failed fusion of NE
NE
NE NE
NE
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fect must involve a small clone of cells during neurulation;
and the mechanisms concerned are probably cell-autonomous
i.e., the presence of wild type cells nearby cannot correct the
error within the af fected cells2 0). And 2) the different pheno-
types described below may be due to different molecular
faults. For example, Rac1 and Cdc42 only involve SE fusion;
thus the clinical phenotypes due to their aberrations could be
different from those affecting proteins regulating NE fu-
sion2 0,2 8).
The embryogenetic mechanisms for the subtype FSND
malformations, described in terms of morphological changes
in the embryonic tissue, are as follows (Fig. 2) : 1) a CSDST
develops, when fusion of the SE fails at a focal point, but the
underlying NE fusion has at least been represented by some
intercellular adhesions, and disjunction at this focal point
does not occur. In this situation, closure of the primary neural
tube immediately cranial and caudal to this focal nondisjunc-
tion spot is unhindered, but the gaping SE is persistently
linked with the NE at this focal spot. This link, a midline gap
in the converging SE and, below it, between the dorsal sclero-
myotomes in opposite sides of the embryo, remains very nar-
row. Further unimpeded development of the surrounding
normal full-thickness dorsal myofascial tissues around the
midline strip progressively sets the primary neural tube into
its normal, primarily intraspinal location. However, a dorso-
median tract of SE tissue persists as the original link between
the closed primary neural tube and the still slightly gaping ep-
ithelial surface. The tract is firmly anchored on the SE side be-
cause its component cells are still essentially part of the SE,
but its deep-end attachment to the NE cells after closure of the
neural groove may not be firm. The deep end of the tract
could therefore be dislodged from the underlying neural tube,
by cellular movements during normal development of the
neural crest cells, meninges and scleromesoderm; so that the
inner anchorage of the tract may end short of the spinal cord
but on the meninges or even the musculofascial layers.
2) A LDM develops, when the fusion of the NE fails at a fo-
cal point but the overlying SE fusion has at least been repre-
sented by some intercellular adhesions, and disjunction at this
focal point also does not occur. Like the reverse of the devel-
opment of a CSDST, the SE gap is closed, but because NE fu-
sion and disjunction never happen at the focal spot, the NE
remains linked with the SE at the spot. This link, a midline
gap in the converging NE and, above it, between the dorsal
scleromyotomes in opposite sides of the embryo, remains very
narrow. Further unimpeded development of the surrounding
normal full-thickness dorsal myofascial tissues around the
midline strip progressively also sets the primary neural tube
into its normal, primarily intraspinal location.
However, a dorsomedian tract of NE tissue (vs. SE tissue in
CSDST) persists as the original link between the focally gap-
ing primary neural tube and the closed epithelial surface24).
The tract is attached on the undersurface of the SE, and affects
the integration of mesodermal tissue at that focal area to form
normal full-thickness skin.
3) A tract with mixed LDM and CSDST develops, when fu-
sion of NE and SE both fail and disjunction never occurs, of-
ten in an “orthodox” manner with the inner portion of the
tract containing NE tissue while the outer tract consisting
mainly of SE. The “pulling forces” along the outer and inner
portions of the tract during embryogenesis will determine the
relative proportion of the two kinds of tissues in the final con-
figuration. However, a “conjoint” ty pe may also occur, where
the entire tract is lined by both SE and NE elements. These
mixed entities are rare but may easily elude detection5 ,11).
4) As for LDM with hidden dermal element - LDMs with
dermal elements but without a sinus tract, the origin of the SE
cells could be from pluripotent cells near the dorsal midline,
or from SE cells somehow being included during the forma-
tion of the LDM stalk5,2 5).
5) FSND with spinal cord lipoma : dorsal spinal cord lipo-
mas have been known to be associated with LDMs, either di-
rectly adjacent to the LDM stalk or continuous with it. Since
both transitional and dorsal lipomas are thought to arise from
premature disjunction, during the same embryogenetic period
as nondisjunction; it is not surprising that nondisjunction and
premature disjunction disorders may coexist25). Equivalent
parallel faults may also account for the coexistence of CSDST
and lipomas.
And 6) FSND with split cord malformation : the fibroneural
stalk or dermal sinus tract found in some cases of split cord
malformation may in fact be the remnant the dorsal portion
of an anomalous ecto-endodermal fistula resulting from aber-
rant early gastrulation21,2 3), which is the embryogenetic basis
for split cord malformation.
Focal Spinal Nondisjunction | Wong ST, et al.
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J Korean Neurosurg Soc 64 (2) : 151-188
PATHOLOGICAL ANATOMY AND CLINICAL
MANIFESTATIONS OF FOCAL SPINAL NONDIS-
JUNCTONAL DISORDERS
Variations in the exact cellular types and histological con-
figurations of FSND lesions account for the spectrum of non-
disjunctional disorders, and partial atresia of a tract may ex-
plain certain variants of the full forms8). Concerning the
documentation of the “level” of a FSND, it should ref lect the
spinal cord level of the initial causative nondisjunctional error,
and accordingly, it should be the level of the laminar defect
through which the fibroneural stalk or sinus tract passes.
Pure CSDST
Pathological anatomy
A dorsal midline dermal sinus tract (a narrow tubular
structure lined by squamous epithelium) is the essential fea-
ture of a CSDST13,4 0). The size of the ostium in the skin of this
tract is variable but usually small (Fig. 3). How deep the tract
penetrates is also variable; over 60% end intradurally, and
some are firmly attached to the spinal cord (Figs. 4-6)43).
Regarding their location along the vertebral column, over
60% of CSDSTs are in the lumbosacral spine; the rest are dis-
tributed over the thoracic and cervical regions4 3). The shape of
a sinus tract on the sagittal plane varies depending on its level
of origin, because the spinal cord ascends along the vertebral
column for a fair distance during development due to their
discrepant growth rates. A lumbosacral CSDST typically takes
on a V-shape with the apex pointing at exactly the laminar
level of its nondisjunctional error; its subcutaneous tract de-
scends caudally to reach the lamina, and from thence it as-
cends towards the thecal sac. With more cranial lesions, the
subcutaneous tract becomes progressively more horizontal
until it points cranially towards the dura in cervico-thoracic
lesions. At the skin level, other skin stigmata may sometimes
accompany the sinus ostium (Fig. 3). At the laminar level, the
tract may pass through the interspinous ligament, or through
Fig. 3.
A : Dermal sinus ostium, appeared as a pin-point area of dr y
scaling with surrounding red discoloration, but without soft tissue swelling.
B : Magnied view of (A). C : Dermal sinus ostium, appeared as a dot of dark
discoloration with surrounding hypertrichosis and pigmentation. Keratin
material could be seen with light compression. D : Magnied view of (C).
Reused from Wong et al.
43)
with permission from Springer Nature.
A
C
B
D
Fig. 4.
MRI images of a 22-month-old with a dermal sinus tract, which as
confirmed intraoperatively, has the skin ostium at L5 spinous process
level (Fig. 3A and B), passes along the caudal aspect of L5 laminae, and
terminates on the dorsal surface of the conus. A : Mid-sagittal T2-
weighted MRI image showing a tiny T2 hypointense intradural nodule at
L1/L2 vertebral level (long arrow), and another slightly larger one at L4
vertebral level (short arrow). The intradural dermal sinus tract is beyond
the resolution power of MRI. B : Paramedian sagittal T2-weighted MRI
image showing a dermal sinus tract from the skin ostium extending into
the subcutaneous fat (arrowhead). C : T1-weighted MRI with gadolinium
injection image, corresponding to A, showing that only the L4 lesion
(short arrow) and the end of the thecal sac become enhanced due to
active inflammation. Reused from Wong et al.
43)
with permission from
Springer Nature. MRI : magnetic resonance imaging.
A B C
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Fig. 5.
Right panel: 16 serial T2-weight MRI axial cuts over the lumbosacral region of the patient shown in Fig. 4. Only the L4 nodule (short arrow), the
skin ostium and subcutaneous tract (arrowheads), and vaguely the L1/L2 nodule (long arrow) are demonstrable by MRI. Left panel : T2-weighted MRI
image with cut lines numbered 1 to 16. Reused from Wong et al.
43)
with permission from Springer Nature. MRI : magnetic resonance imaging, L4 : left
lamina of L4 vertebra, L5 : left lamina of L5 vertebra.
Fig. 6.
MRI images of a 20-month-old with a dermal sinus tract. A, C, and D : T2-weighted MRI images. B : T1-weighted MRI image. Although there is
marked abnormal signal at the skin level, the skin ostium is tiny (Fig. 3C and D). There is a 2 vertebral levels difference between the skin ostium and
where the tract located at the laminar level. The intradural tract (long arrows) appears as a structure that is slightly thicker and more T2 hypointense
than normal nerve roots. Arrowheads indicated that the subcutaneous portion of the dermal sinus tract. Reused from Wong et al.
43)
with permission
from Springer Nature. MRI : magnetic resonance imaging.
A
C
B D
Focal Spinal Nondisjunction | Wong ST, et al.
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J Korean Neurosurg Soc 64 (2) : 151-188
a bifid spinous process or lamina. The tract then penetrates
the dura but can also run between the dural layers for a short
length before becoming intradural. Within the thecal sac, it
may be adherent to the nerve roots or filum and, until proven
otherwise, one should always assume all sinus tracts reach the
spinal cord. Any where along the sinus tract, a dermoid cyst
may form from existing keratin material, and it can even be
intramedullary (Fig. 7). In a report of ten intramedullary spi-
nal dermoid cysts, nine had a traceable CSDST7). The rare oc-
currence of spinal dermoid cyst without a sinus tract is proba-
bly due to isolated sequestration of pluripotent SE cells or
atresia of the outer tract8).
Histologically, a dermal sinus tract is lined by keratinizing
stratified squamous epithelium (Fig. 8A and B). Other com-
ponents in variable abundance include hair follicles and
shafts, mesenchymal derivatives such as blood vessels and fi-
brous tissue (Fig. 8A-C), and occasionally even nerve fibers.
Keratin material fills the lumen of the tract and the cavity of
dermoid cysts (Fig. 8D). Sometimes, the lumen of part of the
tract may be obliterated (Fig. 8C). In slender tracts, a transi-
tional zone of epithelial to non-epithelial tissues can be ob-
served over the tract’s deep end (Fig. 8E). Within the CSDST,
inflamed granulation tissue containing mixed neutrophils,
plasma cells, lymphocytes, and histiocytes is consistently
found (Fig. 8A-C)4,13 ,38). It is due to chemically induced inflam-
mation from keratin accumulation, and may also be second-
ary to bacterial infections from sinus tract’s communication
with the skin surface.
Clinical manifestations
The age of presentation has a wide range; in most series, the
mean is 3 years or below, with some patients f irst diagnosed in
their 30’s or even 50’s43). The commonest presentation is skin
stigmata, usually a cutaneous pit, frequently associated with
pigmentation, haemangioma, skin tag, subcutaneous lipomas,
or hypertrichosis (Fig. 3). Associated subcutaneous lipoma
should arouse the suspicion for an associated spinal cord lipo-
ma, and hypertrichosis for split cord malformation. In many
published series, over 40% of patients had neurological def i-
cits involving limbs and/or bowel and bladder. In infected cas-
es and in patients harbouring large intradural epidermoid/
dermoid cysts, neurological deficits may arise catastrophical-
ly43).
In actual practice, there is uncommonly a definitive history
Fig. 7.
MRI images of a 25-month-old with a large intradural dermoid cyst. A and B : T2-weighted images. C : T1-weighted image. D and E : T1-weighted
with gadolinium injection. The dermoid cyst, spanning 5 vertebral levels, extends from L3 to S2. It is heterogenous in signal intensity, but the main bulk
of it is T2-hyperintense, mildly T1-hypointense, and demonstrates periphery gadolinium enhancement. There is also marked gadolinium enhancement
in the subcutaneous tissue signifying active inammation. The intradural dermoid cyst communicates with an outside dermal sinus tract at the caudal
aspect of the S1 laminae (white arrowhead in E). Reused from Wong et al.
43)
with permission from Springer Nature. MRI : magnetic resonance imaging.
A B C D E
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of discharge from a sinus ostium, which is seen only in 25% of
cases; and even rarer, inflamed skin around an obviously in-
fected ostium or a deep-seated abscess, which occurs in less
than 15%. Paradoxically, in some series, a history of recurrent
meningitis or active meningitis is found in up to 40% of cas-
es43).
Pure LDM
Pathological anatomy
The two constant features of all LDMs are 1) a cutaneous
stigma and 2) an underlying fibroneural stalk anchoring the
spinal cord to the skin lesion (Fig. 9). The cutaneous marker, a
pearly crater of abnormal skin, commonly known as a “ciga-
Fig. 8.
Histological slides. A : Section through the most superficial portion of a dermal sinus tract. B : The portion of the dermal sinus tract in the
intraoperatively identied subcutaneous tissue. C : The intradural portion of a dermal sinus tract (DST). A : The intradural portion of a DST. D : A dermoid
cyst formed along a slender dermal sinus tract (the L1/L2 lesion in Fig. 4). E : The deepest end of a dermal sinus tract where a transition from
epithelialized tissue to connective tissue totally devoid of it can be seen (haematoxylin and eosin stain). Reused from Wong et al.
43)
with permission from
Springer Nature.
A
B
C
D
E
Focal Spinal Nondisjunction | Wong ST, et al.
159
J Korean Neurosurg Soc 64 (2) : 151-188
rette-burn scar/mark”, is due to hindrance on normal skin
development by the stalk attaching to the undersurface of the
SE (Fig. 2). In all instances, the f ibroneural stalk, extending
from the deeper side of the abnormal skin, ultimately merges
with the spinal cord. Only one example of a discontinuous
stalk has been documented8). In all LDMs, the spinal cord is
tethered to the surface myofascial tissue by the fibroneural
stalk22,34,35) and by the meningeal and other mesenchymal in-
vestments condensed around the stalk. The merge point of the
stalk with spinal cord is always above the conus, indicative of
this being due to faulty primary neurulation25). If there are le-
sions truly arising from secondary neurulation defects, but
mimicking the morpholog y of a LDM, they should be classi-
fied as a different entity9,27).
LDMs can be categorized by the external appearance of
their skin lesion into flat (non-saccular) or saccular (Fig. 9).
The f lat LDM is recognisable either by a simple pin-point pit
or a wider crater with “non-skin” squamous epithelium. In-
ternally, the fibroneural stalk passes through the deep fascia, a
bifid lamina/ the interspinous ligament, and the dura (Fig. 10).
The intradural stalk of a lumbosacral lesion is seen, on mag-
Fig. 9.
Classication of limited dorsal myeloschisis (LDM) into non-saccular and saccular types, according to the 2 universal features of LDMs, one
external, one internal. The top images depict the various skin signatures of either crater, pit, or the subtypes of sacs. The bottom images feature the
internal broneural connections between the skin lesion and the spinal cord. Reused from Pang et al.
25)
with permission from Springer Nature.
Non-saccular Saccular
Limited dorsal myeloschisis
Thick
squamous top
Basal noduleNeural stalk Stalk to dome Myelocystocoele
Crater Thin squamous
top
Pit Dome
pit
Membranous
sac
Fig. 10.
Lumbar non-saccular (at) limited dorsal myeloschisis (LDM). A :
Sagittal MR showing subcutaneous fibroneural stalk going through
laminar defect opposite L
3/4
, entering dura opposite L
3
, and joining spinal
cord at L
2
. B : Axial image where LDM stalk joins spinal cord. Note
trapezoid shape of the cord-stalk junction. C : Intradural LDM stalk dorsal
to the conus (low-lying). D : Intradural LDM stalk dorsal to thickened
filum. E : Extradural LDM stalk at laminar defect. Reused from Pang et
al.
25)
with permission from Springer Nature.
LDM joining
cord
Stalk at
fascial
defect
Conus
LDM
Filum
LDM
A
B
C
D
E
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netic resonance imaging (MRI), as a separate longitudinal
structure dorsal to the filum and, more rostrally, dorsal to the
conus (Fig. 10A); at the stalk-cord union (merge point), it a
trapezoid shape on axial MRI (Fig. 10B). The fibroneural stalk
is V-shaped on the sagittal plane, similar to the observation in
CSDST, when it is in the lumbosacral region (Fig. 11); but it
becomes progressively horizontal or slanting upwards when
located more cranially (Fig. 12). The tethering effect to the
cord can be very obvious when the fibroneural stalks are stout
(Fig. 13), or when the cord is tented dorsally at the stalk-cord
merge point (Fig. 14). In rare cases, the stalk appears to pull
the cord archly dorsally towards the skin lesion to the extent
that the cord seems to have deformed the overlying bone and
myofascial layers (Fig. 15). In all these examples, the apparent
dynamism of the tethering is obvious.
The saccular LDM arises with the initial embryogenetic ar-
chitecture of a f lat LDM, but the increasing hydrodynamic
pressure of cerebrospinal f luid (CSF) soon changes its ana-
tomical configuration drastically. CSF may be forced up along
the slender dural sleeve surrounding the stalk, or through the
Fi g. 11.
Three cases of lumbar at limited dorsal myeloschisis (LDM) with
V-shaped course of the LDM stalks. Left : Crater is at L
4/5
, stalk enters
thecal sac at S
1
, and joins spinal cord at upper margin of L
2
. Middle :
Crater at L
3/4
, stalk enters dura probably at L
5
/S
1
, and joins spinal cord at
L
2
. Right : Crater at L
4/5
, stalk enters dura around L
5
/S
1
, and joins spinal
cord at L
3
. Reused from Pang et al.
25)
with permission from Springer
Nature.
Fig. 12.
Upward coursing limited dorsal myeloschisis (LDM) stalk in a
thoracic at LDM. A : Sagittal image shows skin crater at L
1
, extradural stalk
at T
12
, dural entrance of the stalk above T
12
, and joining of stalk to spinal
cord at T
10
. B-E : show axial image of the LDM stalk at corresponding points
shown in (A). Reused from Pang et al.
25)
with permission from Springer
Nature.
Intradural
stalk
Extradural
stalk
Subcutaneous
stalk
Syrinx
A
B
C
D
E
Fig. 13.
Thick upward slanting broneural stalk in a thoracolumbar (T
11
/
T
12
) LDM. Reused from Pang et al.
25)
with permission from Springer
Nature. LDM : limited dorsal myeloschisis.
LDM
Stalk
Fig. 14.
Upper thoracic crater type limited dorsal myeloschisis (LDM)
showing dorsal tenting of both the dural sac and spinal cord at the site
of the stalk-cord junction, giving the appearance of taut tethering of the
cord. Left : T
1
sagittal MRI. Middle : T
2
sagittal MRI. Right : Axial MRI. Note
skin crater, subcutaneous tract and intradural course of the stalk are well
shown on the T
2
sagittal image. Also, fat is seen within the stalk. Reused
from Pang et al.
25)
with permission from Springer Nature. MRI : magnetic
resonance imaging.
Stalk
Skin crater
Focal Spinal Nondisjunction | Wong ST, et al.
161
J Korean Neurosurg Soc 64 (2) : 151-188
potential space within the fibroneural stalk’s core to reach and
distend the overlying skin into a fluctuant sac. Internally, the
“sac” of saccular LDMs can have 3 types of content. First, the
content is a segmental myelocystocoele : when the portion of
the cord bearing the dorsal myeloschisis has an associated hy-
dromyelia, the central lumen of the fibroneural stalk may be
Fig . 16.
Formation of saccular limited dorsal myeloschisis (LDM) with segmental myelocystocoele. Fluid from hydromyelic cavity in the underlying
spinal cord dissects through the potential tubular space within the original cutaneo neuroectodermal tract and subsequently balloons out into an
ependyma-lined myelocystocoele, a sac within an outer sac of distended subarachnoid cerebrospinal uid. The sac is covered by a full-thickness skin
base and a thickened, distinctly different squamous epithelial dome. Reused from Pang et al.
25)
with permission from Springer Nature.
Myelocystocoele
Cutaneous-neuroectoderm
junction
Thickened squamous
epithelium
Subarachnoid space
Dural stula
Hydromyelia
within cord
Full thickness skin
Hydromyelic cavit y
extends into centre of
original
non-disjunctioned LDM
stalk
Fig. 15.
T
5
LDM with non-saccular skin crater showing extreme dural
displacement and kinking of the thoracic cord presumably due to
“
pull
”
by a short, stout broneural stalk. Left : T
1
sagittal MRI. Right : T
2
sagittal
MRI. This child had early neurological decits. Reused from Pang et al.
25)
with permission from Springer Nature. MRI : magnetic resonance
imaging.
Fi g. 17.
Computed tomography myelogram of a cervical saccular limited
dorsal myeloschisis with segmental myelocystocoele. The myelocystocoele
sac does not contain contrast material, which remains in the subarachnoid
space. Reused from Pang et al.
25)
with permission from Springer Nature.
Myelocystocoele Subarachnoid
space
J Korean Neurosurg Soc 64 | March 2021
162 https://doi.org/10.3340/jkns.2020.0117
Fig . 19.
Lumbar saccular limited dorsal myeloschisis with segmental myelocystocoele and lipoma in a 2.5-year-old boy. A and B : Sagittal T2-weighted
MRI. C-E : Axial T1-weighted MRI. MRI : magnetic resonance imaging.
A
C
D
EB
Myelocystocoele
Myelocystocoele
Hydromyelic
cord
Intact conus
caudal to
myelocystocoele
Lipoma
Fig . 18.
High thoracic saccular limited dorsal myeloschisis with segmental myelocystocoele. A-D : Pre-operative. A : Photo showing the sac with the
epithelial dome. B : Sagittal T2-weighted MRI. C : Axial T1-weighted MRI. D : Axial T2-weighted MRI. E-G : Postoperative MRI images. E : Sagittal T1-
weighted MRI. F : Sagittal T2-weighted MRI. G : Axial T1-weighted MRI. MRI : magnetic resonance imaging.
A
E F G
B D
C
Epithelial
dome
Skin base
Site of
non-disjunction
Focal Spinal Nondisjunction | Wong ST, et al.
163
J Korean Neurosurg Soc 64 (2) : 151-188
distended by CSF into a large myelocystocoele housed in an
epithelium-covered sac (Fig. 16). This type is most commonly
found in the cervical region (Figs. 17-19)29,34 -36). Second, it has a
basal neural nodule. When there is no hydromyelia, the fibro-
neural stalk and its central lumen remain compressed and
narrow in its deeper course, but the superficial portion of the
stalk swells into a f luid sac with basal neural nodules at its
base, while retaining the original nondisjunctional attach-
ment to the cutaneous epithelium (Figs. 20 and 21)21,22 ,30 ,3 4).
Third, it has a slender fibroneural stalk traversing the CSF sac
to reach its dome (stalk-to-dome) : least commonly in saccular
LDMs without hydromyelia, the normal meninges around the
neural tube extends to ensheath the fibroneural stalk, and
projects to reach the SE. CSF squeezes into the dural fistula
containing the fibroneural stalk and ultimately distends the
thinner, less well-supported squamous epithelial membrane
on the surface into a CSF-filled, skin-based but epithelium-
capped sac. Strands of the fibroneural stalk traverse the fluid
cavity of the sac to reach the part of the dome bearing the edge
of the crater, where the nondisjunction occurred (Fig. 22).
Depending on the f luid pressure and the thickness of the
Fig. 20.
Formation of a saccular limited dorsal myeloschisis (LDM) with basal neural nodule. In these cases, cerebrospinal uid (CSF) dissects along the
dural stula ensheathing the broneural stalk and balloons out the less well suppor ted midline epithelial layer to give a CSF-lled sac, whose base is
skin-covered. The neuroectoderm at the original site of non-disjunction swells to become the basal neural nodule. Reused from Pang et al.
25)
with
permission from Springer Nature.
Basal neural nodule
Original cutaneous
neuroectoderm junction
Thickened squamous epithelium
Subcutaneous fat
Dorsal musculature
Dorsal fascia
Neural stalk
Dura
Skin
CSF
Bid neural arch
Arachnoid
Dural stula (extension)
• Patent dural sleeve
around LDM stalk
• CSF sac with basal
neural nodule
Fig. 21.
Cervical saccular limited dorsal myeloschisis (LDM) with basal
neural nodule within the base of the cerebrospinal fluid sac at the
original non-disjunction site between cutaneous and neural ectoderms.
Reused from Pang et al.
25)
with permission from Springer Nature.
Basal nodule
LDM stalk
J Korean Neurosurg Soc 64 | March 2021
16 4 https://doi.org/10.3340/ jkns.2020.0117
apical epithelium and adjacent skin, the sac wall varies from
the coarse, purplish, corrugated cap in the not-so-turgid tu-
bular structures in many cervical saccular lesions, to the
translucent membrane topping a tense lumbar sac, and finally
to the giant, diaphanous bubble. A transitional form between
saccular and flat LDMs can be observed, due to transient in-
crease in fluid pressure during straining, in flat LDMs with
the intermittently ballooning central crater (Fig. 23).
As with CSDST, registration of the spinal level of LDMs has
been far from ideal. The challenge is due to the great differ-
ence in the level of the skin lesion, the level where the f ibro-
Fig. 22.
Thoracic saccular limited dorsal myeloschisis with neural stalk
that traverses the cerebrospinal fluid sac and reaches the small skin
crater at the top of the cystic dome, presumably the original site of
disjunction failure. Reused from Pang et al.
25)
with permission from
Springer Nature.
Neural
stalk
Crater
Fig. 23.
Lumbar limited dorsal myeloschisis (LDM) showing a
cerebrospinal uid-lled
“
bubble
”
topped by squamous epithelium that
distends only on straining. Note site of cord-stalk union is with slight
dorsal
“
hump
”
on the cord outline, and a neurenteric cyst (Neu) right at
this site. Reused from Pang et al.
25)
with permission from Springer Nature.
Skin bubbleStalk
LDM
LDM
Neu
Fig. 24.
Distribution of LDMs along the spinal axis. Designation of location is determined by the vertebral level where the broneural stalk attaches to
the spinal cord. Note the two peaks at L
2
–L
4
and C
5
–C
7
, and the absence of sacral lesion. Reused from Pang et al.
25)
with permission from Springer Nature.
LDM : limited dorsal myeloschisis.
9
8
7
6
5
4
3
2
1
0
C1 C2 C3 C4 C5 C6 C7 T1 T2 T3 T4 T5 T6 T7 T8 T9 T10 T11 T12 L1 L2 L3 L4 L5 S1 S2 S3 S4 S5
Spinal level
Distribution of LDMs (n=63)
No. of patients
Focal Spinal Nondisjunction | Wong ST, et al.
165
J Korean Neurosurg Soc 64 (2) : 151-188
Fig. 26.
Histopathology of limited dorsal myeloschisis (LDM) stalk (haematoxylin and eosin stain). A : Core of glial tissue with a large neuron, framed by
brous tissue. B : Nests of glial tissue (Gl) embedded in a dense brous matrix. C : LDM stalk showing a longitudinal glial core (Gl) containing neurons
(Neu). A peripheral nerve (arrows) issues forth at right angle to the glial core as from a
“
real
”
spinal cord. D : LDM stalk containing glial tissue (Gl) and a
large dorsal root ganglion (DRG). E : Peripheral nerves (N) with Pacinian corpuscle within LDM stalk. Pacinian corpuscle in the stalk indicates the nerves
involved in LDM formation are indeed sensory nerves likely from the adjacent neural crest. Reused from Pang et al.
25)
with permission from Springer Nature.
A
B
C
D
E
Fig. 25.
Distribution of the four types of LDM classied according to external and internal features and assorted by regions of the spinal axis. The four
types are f lat (non-saccular), saccular with basal neural nodule, saccular with neural stalk reaching the cyst dome, and saccular with segmental
myelocystocoele. Note preponderance of the at LDM in the lumbar and lower thoracic regions. Saccular types are seen in both cervical and lumbar
segments. The regions of the vertebral column are coded as : cervical (C1–C7); thoracic-up (T1–T5); thoracic-lo (T5–T11); thor-lumb (T12–L1); lumbar (L1–
L5). Reused from Pang et al.
25)
with permission from Springer Nature.
20
15
10
5
0
Flat
(non-saccular)
Saccular-
basal-nodule
Saccular-
dome-stalk
Saccular-
myelocystocoele
Tumb ar
Thor-lumb
Thoracic-lo
Thoracic-up
Cervical
J Korean Neurosurg Soc 64 | March 2021
166 https://doi.org/10.3340/jkns.2020.0117
neural stalk passes through the lamina or penetrates the dura,
and where it merges with the spinal cord. In the largest LDM
series published25), the vertebral level where the stalk merges
with the spinal cord was chosen as the level of the LDM be-
cause it is usually the most unequivocal feature on MRI. The
locations of the LDMs in that series are shown in Fig. 24, while
the distribution of the types of LDMs is depicted in Fig. 25.
Over two-thirds of LDMs in that series are located in the low-
er half of the spinal cord2 5).
Histologically, the central feature of all LDM stalks is neu-
roglial tissue, a hallmark of the stalk’s origin from the NE. It is
either in large elongated swaths containing scattered neurons
(Fig. 26A), or in nests embedded in dense fibrous tissue (Fig.
26B). Also found in every stalk is a prof use network of periph-
eral nerves randomly admixed with the glial nests, but in
some cases, nerves are seen emanating from a central core of
neuron-containing glia likened to an abortive spinal cord (Fig.
26C). Large nodules of dorsal root ganglion cells are seen in
some cases, attesting to the occasional entrapped neural crest
stem cells during formation of the neural stalk (Fig. 26D). Pa-
cinian corpuscles (Fig. 26E) seen amongst some of these
nerves suggest they are indeed sensory axons. Evidence of
mesenchymal condensation around the lengthening neural
stalk is shown by the almost universal inclusion of numerous
fibrous bands, skeletal muscle, fat (Fig. 27A), and prominent
vascular channels sometimes in the form of a vascular glomus
(Fig. 27B). Glioependymal tissue lines the sac cavities in cases
of segmental myelocystocoeles (Fig. 27C). The cutaneous “cig-
arette-burn mark” has the histological appearance of a dermal
layer with engorged vascularity, abundant nerve fibres, and an
abnormal collagen f iber matrix. The unevenness of its surface is
due to the ruggedness of the epidermis and dermis (Fig. 28)16,17).
The question is sometimes asked what constitute the mini-
mum criteria for a diagnosis of LDM. It has been shown that
there are patients with clinical and radiological features of
LDM (Figs. 29 and 30) and most of its histological features in-
cluding periphery nerve fibers, but no glial tissue within the
sta lk (Fi g. 31)10 ,16,17). In many of these patients, melanocytes are
also a prominent feature. Since periphery nerves and melano-
cytes are neural crest derivatives, and neural crest cells are lo-
cated in the primary neural tube over the dorsal midline, a
nondisjunctional stalk might drag with it neural crest progen-
Fi g. 2 7.
Histopathology of limited dorsal myeloschisis (LDM) stalk (haematoxylin and eosin stain). A : LDM stalk containing skeletal muscle (M), fat (F),
and brous band (FB). B : LDM stalk containing prominent blood vessels (V) within a core of glial tissue (Gl), and brous bands (F), in the form of a
vascular glomus. C : Glioependymal lining of a segmental myelocystocoele in a lumbar saccular LDM. Reused from Pang et al.
25)
with permission from
Springer Nature. Epen : ependyma, Gl : glial tissue.
A B C
Fig. 28.
IHistological slide of a skin
“
cigarette burn mark
”
showing
increase vascularity, plenty of nerve bres (yellow arrows), and a different
collagen pattern, comparing to the adjacent normal dermis. Yellow
dashed line marks the border between normal and abnormal dermis.
Gross appearance of the skin lesion is shown in Fig. 29A (haematoxylin
and eosin stain). Reused from Wong et al.
43)
with permission from
Springer Nature.
Normal
dermis
Subcutaneous sof t tissue EpidermisDermis
Focal Spinal Nondisjunction | Wong ST, et al.
167
J Korean Neurosurg Soc 64 (2) : 151-188
Fig. 29.
A case of
“
clinical and radiolgical
”
limited dorsal myeloschisis (LDM). A : Cigarette burn mark. B : Mid-sagittal T2 weighted MRI image showing
the intradural portion of the LDM stalk (yellow arrow). Blue arrow means the conus. C : Sagittal MRI just next to B showing the subcutaneous portion of
the stalk (white arrow). D : Axial T2-weighted MRI images corresponding to the cut lines in (B). Reused from Wong et al.
43)
with permission from Springer
Nature. MRI : magnetic resonance imaging.
A
B C D
Fig . 31.
Histological slide of the intradural portion of a limited dorsal
myeloschisis stalk showing the presence of nerve fibres and blood
vessels. Intraoperative photograph is shown in Fig. 30 (haematoxylin and
eosin stain). Reused from Wong et al.
43)
with permission from Springer
Nature.
Blood vessels
Connective tissue
Nerve bres
Fig. 30.
Intra-operative photographs showing excision of a LDM with a L2L3 laminoplasties. Pre-operative MRI images and the skin lesion are shown in
Fig. 29. The skin lesion was traced to the supraspinous ligament of S1 only; the S1 laminae were untouched. This kind of limited exposure thus left a
small segment of the LDM stalk in situ. Reused from Wong et al.
43)
with permission from Springer Nature. LDM : limited dorsal myeloschisis, MRI :
magnetic resonance imaging.
A B C
Intradural por tion of LDM
Tip of the conus
Cut end of the lum
Cut end of LDM s talk
Filum
J Korean Neurosurg Soc 64 | March 2021
168 https://doi.org/10.3340/ jkns.2020.0117
itor cells without neuroglial progenitor cells2,30,31,37). Thus the
diagnosis of LDM can probably be applied in these patients
with periphery nerve f ibers but no glioneuronal tissue in the stalk.
Clinical manifestations
Most LDM patients also present at a young age. In a series
with a total of 63 patients, the mean age at presentation of 56
children was 5.9 years; and that of seven adults was 28.2 years.
About half of LDM patients are neurologically intact at pre-
sentation, which underscores the importance of the cutaneous
marker as an initial diagnostic clue25). The “pathognomic” cu-
taneous marker in both f lat and saccular LDMs is a confined
area of abnormal epithelium over the dorsal midline. In f lat
LDMs, the cutaneous lesion can be a conspicuous crater or a
tiny pit. 1) Crater : the commonest skin abnormality in f lat
LDMs is a sunken crater on the flat skin surface made of
pinkish squamous epithelium (Fig. 32A and B), of ten with el-
evated skin margin (Fig. 32C) and sometimes surrounded by a
capillary haemangioma with irregular corrugated borders
(Fig. 32D) or hyperpigmented skin (Fig 32E). There are occa-
sionally long hair emanating from the crater (Fig. 32F), and
some craters are edged by hooded overhanging skin (Fig. 32G).
Fig. 34.
Subtle pit (within circle) in a flat lumbar limited dorsal
myeloschisis with no surrounding exuberance. Reused from Pang et al.
25)
with permission from Springer Nature.
Fig. 32.
Flat type skin lesions in limited dorsal myeloschisis. A : Sunken
crater of pale squamous epithelium. B : Sunken crater of pale epithelium.
C : Squamous epithelial crater with rim of elevated skin borders. D :
Crater surrounded by prominent capillary haemangioma with irregular
corrugated borders. E : White non-melanotic, epithelial crater with
surrounding hyperpigmented skin. F : Crater covered with long hair
arising from the rim of surrounding full-thickness skin. G : Crater with
surrounding skin overhang (arrow). Reused from Pang et al.
25)
wit h
permission from Springer Nature.
A B
C D
E F G
Fig. 33.
Flat LDMs with transitional skin lesions: A : Lumbar LDM with a
flat epithelial crater and an adjacent area made of stretchable, non-skin
epithelium (Mem) that distends into a small CSF-filled bubble when the
patient strains. B : Pink epithelial crater slightly distended into a small blister
by underlying CSF. Reused from Pang et al.
25)
with permission from Springer
Nature. LDM : limited dorsal myeloschisis, CSF : cerebrospinal uid.
A B
Crater
Mem
Focal Spinal Nondisjunction | Wong ST, et al.
169
J Korean Neurosurg Soc 64 (2) : 151-188
In several examples, the crater is adjacent to an area of wrin-
kly, over-stretched skin that periodically distends with CSF on
dependent posturing or straining (Fig. 33A). Very rarely, the
centre of the crater is adorned with a CSF-filled blister (Fig.
33B), which is transitional form between f lat and saccular le-
sions. And 2) pit : the most subtle skin abnormality in a flat
LDM is a small midline pit with no other unusual features
(Fig. 34), easily missed on cursory examination, and might be
confused with a CSDST ostium. Sometimes the pit situates
within a capillary haemangioma. Pit lesions are usually found
in low thoracic and lumbar cases.
Externally, saccular LDMs usually appear as a skin-based
sac, but rarely as a translucent membranous sac. 1) Skin-based
sac : the sac wall is thick, skin-based with a dome that is dis-
tinctly abnormal skin. The appearance of the dome cover can
be roughly subdivided into three subtypes. One subtype has a
wide top of purplish, raw-looking, thick stratif ied squamous
epithelium (Fig. 35A). A second subtype has a much smaller,
pale, discrete, puckered crater of squamous epithelium on the
dome (Fig. 35B). A third subtype has a small, almost imper-
ceptible patch of ultra-thin epithelium on the apex of the rela-
tively delicate skin-based dome (Fig. 35C). And 2) membra-
nous sac : this type should be managed urgently as an “open”
spinal dysraphic lesion, but the fibroneural stalk should not be
missed. An example is a tubular, CSF-filled sac made of a di-
aphanous membrane resembling thickened arachnoid, pro-
truding through a 4 mm skin-lined dorsal defect (Fig. 36). The
base of this sac has a shallow collar of skin similar to the skin-
based sacs. The locations and types of the cutaneous lesions
are summarized in Table 1.
It is noteworthy that other cutaneous markers of dysra-
phism such as hypertrichosis, capillary haemangioma, or mis-
aligned gluteal crease are never seen alone in LDM without
the quintessential epithelial crater or pit. The pearly midline
crater in a non-saccular LDM thus remains the single most
important diagnostic clue for LDM, especially before the de-
velopment of neurological symptoms.
LDMs cause neurological deficits solely by their tethering
effect, which vary in kind and severity by the spinal level of
the LDM. In general, LDM patients tend to have milder dis-
Fig. 36.
Lumbar limited dorsal myeloschisis (LDM) with membranous sac. A : Large ruptured sac made of diaphanous membrane. B : Close-up of the
base showing a small skin defect through which protrudes a tubular basal neural nodule. C : The entire LDM is exposed at surger y to show basal neural
nodules (BN), subcutaneous tract, and intradural stalk (S) attached to the spinal cord. Reused from Pang et al.
25)
with permission from Springer Nature.
A B C
Fig. 35.
Saccular skin lesions in limited dorsal myeloschisis (LDM). A : A cervical saccular LDM with full-thickness skin at the base and coarse, thick,
corrugated purplish squamous epithelial top. Cervical saccular lesions are usually not turgid. B : An upper thoracic saccular LDM with mostly skin except
for a dome crater of squamous epithelium. C : A turgid lumbar saccular LDM with a skin base and a translucent
“
non-skin
”
epithelial top. Reused from
Pang et al.
25)
with permission from Springer Nature.
A B C
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170 https://doi.org/10.3340/jkns.2020.0117
ability than patients with other forms of dysraphic malforma-
tions such as split cord malformations and spinal cord lipo-
mas. In Pang et al.’s series25), half of the LDM patients had
neurological deficits at presentation. About 10% of patients
had significant weakness and neuropathic bladder, and the
rest of the patients had mild or tolerable neurological or uro-
logical deficits, with relatively little hindrance to their lifestyle.
The correlations between the types of deficits and locations of
the LDMs are summarized in Table 2. The proximity of ten-
sion to the relevant cord segments does seem to correspond
with the kind of deficits. For example, only cervical lesions
produce hand and arm weakness; leg weakness is seen in only
9% of cervical lesions, but 22% in upper thoracic lesions, 38%
in thoracolumbar lesions, and 50% in lumbar lesions; and
bladder dysfunction is seen in approximately 15% of lower
thoracic and lumbar lesions but not in cervical or upper tho-
racic lesions. Lumbar LDMs close to the conus are perhaps
more treacherous because they more often implicate the blad-
der yet are more likely to be occult.
Tab le 2 .
Typ es of neurological decits in different LDM locations (n=63)
Neurological status
Number of patients assorted by LDM location
Cervical
(n =11)
Thoracic upper
(n=9)
Thoracic lower
(n=7)
Thoracolumbar
(n=8)
Lumbar
(n=28)
Normal 4 (36.0) 2 (22.0) 4 (57.0) 4 (50.0) 14 (50.0)
UE weakness/sensory loss 7 (64.0) 2 (22.0)
LE weakness 1 (9.0) 2 (22.0) 3 (43.0) 3 (38.0) 14 (50.0)
LE sensory loss 1 (11.0) 2 (31.0) 1 (13.0) 8 (29.0)
Spastic legs 4 (36.0) 4 (44.0) 2 (31.0)
Back pain 1 (25.0) 3 (13 .6)
Foot deformity 2 (9.1)
Scoliosis 2 (31.0) 1 (16. 6) 1 (4.5)
Neurogenic bladder 1 (25.0) 1 (16. 6) 4 (18.0)
Abnormal URD 1 (25.0) 1 (16. 6) 2 (9.1)
Values are presented as number (%). Reused from Pang et al.25) with permission from Springer Nature. LDM : limited dorsal myeloschisis, UE : upper
extremity, LE : lower extremity, URD : urodynamics
Fi g . 3 7.
Linear regression analysis between neurological grade* and
patient age shows a logistical tendency for older patients with limited
dorsal myeloschisis (LDM) to present with higher grades of neurological
decits (correlative coefficient R
2
=0.642). Reused from Pang et al.
25)
with
permission from Springer Nature. *Neurological grading system in LDM :
grade 0, no decits or symptoms; grade 1, mild upper or lower extremity
weakness, or pure sensory deficits
±
pain; grade 2, moderate to severe
upper or lower extremity weakness
±
sensory deficits, or neurogenic
bladder without weakness; grade 3, upper or lower extremity
weakness+neurogenic bladder.
5
4
3
2
1
0
0 5 10 15 20 25 30 35 40
Age (years)
Regression of gr ade by age (R
2
=0.642)
Neurological grade
Tab le 1.
Skin lesions in LDM in different LDM locations (n=63)
LDM location*
Skin Lesions in LDM
Crater Pit Saccular Membranous
sac
Cervical 2 0 9 0
Thoracic-upper 3 2 4 0
Thoracic-lower 4 0 3 0
Thoracolumbar 4 2 2 0
Lumbar 16 4 6 2
Reused from Pang et al.25) with permission from Springer Nature. *The
regions of the vertebral column are coded as: cervical (C1–C7); thoracic-
upper (T1–T5); thoracic-lower (T5–T11); thoracolumbar (T12–L1); and
lumbar (L1–L5). LDM : limited dorsal myeloschisis
Focal Spinal Nondisjunction | Wong ST, et al.
171
J Korean Neurosurg Soc 64 (2) : 151-188
Similar to other cord tethering entities, the probability of
neurological injury increases with longitudinal growth of the
spine and with age. Pang et al.2 5) demonstrated that older pa-
tients with LDMs had a tendency to present with more severe
neurological and urological disabilities; and that infants and
young children were more likely to be neurologically normal
(Figs. 37 and 38). Neurological deterioration was observed in
all four adolescents who had had longitudinal follow-up and
delay of surgery of 1 to 9 years.
Mixed LDM and CSDST, LDM with hidden der-
mal elements, and parallel LDM and CSDST in
close proximity
In 2013, lesions definitely composed of the histological find-
Fig. 38.
Clustered bar graphs showing neurological grade assorted by patients
’
age-groups (birth to 6 months; 6 to 12 months; 1 to 5 years; 6 to 10
years; 11 to 18 years; and over 18 years) within each neurological grade of 0–3. There is a preponderance of younger children with the better
neurological grades and preponderance of older patients with the worse grades. Reused from Pang et al.
25)
with permission from Springer Nature.
20
15
10
5
0
3
2
1
0
Grade
Age groups
No. of patients
0–6 months 7–12 months 1–5 years 5–10 y ear s 10–18 y ear s >18 y ear s
Fig. 39.
Histological constituents of a mixed LDM-CSDST stalk of the
“
orthodox
”
type. Its supercial portion is of typical dermal tissue lying in tandem
with its deeper portion containing mainly glioneuronal tissue. Insets showing both tissues in high power (haematoxylin and eosin stain). LDM : limited
dorsal myeloschisis, CSDST : congenital spinal dermal sinus tract.
Surface
dermal
sinus tr act
Deep
LDM stalk
Dermoid cyst
Squamous epithelium
Glia (neuroectoderm)
Nerve
Mixed LDM and CSDST : “Or thodox” type
Contiguous cutaneous and neuroectoderm
J Korean Neurosurg Soc 64 | March 2021
172 https://doi.org/10.3340/jkns.2020.0117
ings of both LDMs and CSDSTs were f irst described25). They
are rare compared to the pure forms of LDMs and CSDSTs. In
a series of 75 LDM cases, there were five cases of this mixed
type5). In another series of 51 cases that consisted of 40 LDMs
and 11 CSDSTs, another f ive cases were documented11).
Macroscopically, a mixed lesion of LDM and CSDST can
A
LDM-dermal sinus
tract
B
Dermoid cyst
D
Dermoid cyst
C
LDM-dermal sinus
tract
Fig. 40.
MRI images of a 3-month-old girl with a mixed LDM and CSDST –
“
conjoint
”
type. The diagnosis was made based on intraoperative and
histological ndings (Figs. 41 and 42). MRI images can only show a tract extending from the skin to the spinal cord, but cannot conrm the components
of the tract. A and B : Sagittal T2-weighted MRI images. C and D : Axial T2-weighted MRI images. LDM : limited dorsal myeloschisis, CSDST : congenital
spinal dermal sinus tract, MRI : magnetic resonance imaging.
Fig. 41.
Intraoperative photos of a patient (Fig. 40) with a mixed LDM and CSDST –
“
conjoint
”
type. A : Skin pit. B and C : Dissection of the extra-dural
portion of the tract. D : Photo taken at the moment before complete detachment of the tract from the spinal cord. LDM : limited dorsal myeloschisis,
CSDST : congenital spinal dermal sinus tract.
A B
C D
Spinal cord
End of
track
Dura
Cervical pit with yellow-white discharge
Skin pit
Dermoid cyst
LDM-dermal
sinus track
LDM-dermal
sinus track
Focal Spinal Nondisjunction | Wong ST, et al.
173
J Korean Neurosurg Soc 64 (2) : 151-188
mimic either of the pure forms. Even cystic type has been ob-
served11). Thus, their recognition relies on histology. Three
histological types have been documented. In the “orthodox”
type, the dermal and neuroglial elements are in tandem in
their respective embryologically orthodox order, i.e., an outer
tract of CSDST and an inner tract of LDM elements (Fig.
39)11). In the “conjoint” type, the entire FSND tract is lined by
both SE and NE elements (Figs. 40-42). The most treacherous
Fig. 42.
Histological slides of a patient (Fig. 40) with a mixed LDM and CSDST –
“
conjoint
”
type showing the presence of a dermal sinus tract within a
bro-glioneuronal stalk (haematoxylin and eosin stain). LDM : limited dorsal myeloschisis, CSDST : congenital spinal dermal sinus tract.
Dermal sinus tract within bro-glioneuronal stalk Stra tied squamous
epithelium-lined tract
Exocrine
gland
Cheesy
content
Glioneuronal
tissue
Squamous
epithelial sinus
tract with cheesy
content
Fig. 43.
A 15-month-old with a LDM with hidden dermal elements. A : Sagittal T2-weighted MRI showing the appearance of a classic lumbar LDM. B :
Photo showing a crater and surrounding haemangioma. C : Histological slide showing a stalk with glioneuronal core and derivatives of squamous
epithelium (haematoxylin and eosin stain). LDM : limited dorsal myeloschisis, MRI : magnetic resonance imaging.
A
B C
Merge point
Giant cells
Squamous nest
Hair follicles
Glioneuronal
core
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mixed lesions have been observed in which the dermal ele-
ments form microscopic squamous epithelial islands within
the neuroglial tissue of an otherwise proper LDM tract –
“LDM with hidden dermal elements” (Fig. 43)5,3 8). Rarely, par-
allel LDM and CSDST tracts can co-exist in close proximity
from skin to spinal cord (Fig. 44).
The most salient implication in clinical practice with the
discovery of this mixed type is that a mixed lesion cannot be
reliably exonerated at the time of surgery without benefit of
histology. Thus, it seems prudent that in all cases of suspected
LDM, the entire tract is removed from skin to spinal cord. In
addition, all FSND patients should have a delayed post-opera-
tive MRI to rule out a recurrent dermoid cyst.
FSND with spinal cord lipomas, split cord mal-
formations, and other dysraphic malformations
FSNDs have been observed to occur with other dysraphic or
paradysraphic malformations such as spinal cord lipomas,
myelomeningoceles, split cord malformations, and neurenter-
ic cysts (Table 3 and Fig. 45). In such cases, the complex anat-
omy of the other malformations usually dominates the patho-
logical anatomy of the composite malformation, for a pure
FSND lesion is structurally more subtle unless it is a CSDST
with a large intradural dermoid/ epidermoid cyst.
The clinical manifestations of these composite malforma-
tions also follow the usual course of the associated anomalies,
especially when there are only LDM elements without der-
moid cyst. However, if present, the dermal elements can have
Tab le 3.
Associated anomalies in LDM (n=63)
Anomalies
LDM location
Cervical
(n =11)
Thoracic upper
(n=9)
Thoracic lower
(n=7)
Thoracolumbar
(n=8)
Lumbar
(n=28)
SCM 4 1 1
Terminal lipoma 1 1
Dorsal lipoma 1 2 3
Thickened lum 2 1 3 21
Neurenteric cyst 1
Syringomyelia 1 1
Chiari II 3 2
Hydrocephalus 6
Dermal sinus 111
Velum interpositum cyst 1
Vertebral/rib fusion 2 1
Reused from Pang et al.25) with permission from Springer Nature. LDM : limited dorsal myeloschisis, SCM : split cord malformation
Fig. 44.
Intraoperative photos showing the presence of a LDM and a CSDST in parallel. LDM : limited dorsal myeloschisis, CSDST : congenital spinal
dermal sinus tract.
Dermal sinus trac t
Dermal sinus trac t
LDM stalk LDM stalk
Dermal sinus &
LDM stalk inser t
on adjacent sites
on spinal cord
Parallel LDM stalk and dermal sinus tract
Focal Spinal Nondisjunction | Wong ST, et al.
175
J Korean Neurosurg Soc 64 (2) : 151-188
Fig. 45.
MRI images showing a LDM associated with a transitional spinal cord lipoma in an 11-month-old. The axial cuts are numbered according to the
cut-lines on the T2-weighted mid-sagittal MRI image. Arrowheads mean the subcutaneous portion of the LDM stalk. The stalk was confirmed
intraoperatively to pass through bid S1 and S2 laminae. Reused from Wong et al.
43)
with permission from Springer Nature. MRI : magnetic resonance
imaging, LDM : limited dorsal myeloschisis.
T1-weighted MRI
T2-weighted MRI T1-weighted MRI
T2-weighted MRI
Intradur al lipoma
Left
Right
Fig. 46.
Double LDMs, both crater type, with accompanying dorsal lipomas.
The lower LDM is at L
2/3
, and upper LDM is at T
12
. Both accompanying lipomas
are just rostral to the LDM stalk. Reused from Pang et al.
25)
with permission
from Springer Nature. LDM : limited dorsal myeloschisis.
Upper LDM
Upper lipoma
Lower lipoma
Lower LDM
LDM
joins cord
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significant adverse impact due to their inherent risks of in-
flammation, infection, proliferation producing mass effect,
and recurrence if not totally excised. One should therefore al-
ways be vigilant for hidden dermal elements when dealing
with spinal dysraphic malformations.
EVALUATION
A thorough clinical history and physical examination are
paramount to elicit the symptoms and signs of neurological
deficits related to the types and spinal level of FSNDs, past or
active infection, and clues to the existence of associated anom-
alies. Urological assessment including urinalysis, ultrasonog-
raphy of the urinary system, voiding cystourethrogram, and
Fi g . 4 7.
Intra-operative photographs showing excision of a dermal sinus tract (DST) with skip laminectomy technique (MRI images of this patient are
shown in Figs. 4 and 5). B- G : Caudal. H-K : Rostral wound. A : Skin preparation. Yellow lines mean skin incisions. Numbers in black on skin mean levels of
lumbar spinous processes. B : L4L5 laminectomy has been done. The subcutaneous portion of the DST (DSTsc) merging with the dura has been fully
exposed. C : Photography taken after opening the dural sheath enveloping a portion of DST that is lying in the dura mater (DSTdu). D : Photography
showing the arachnoid membrane entry site of the DST. E : After opening the arachnoid membrane, the intradural portion of the DST (DSTintradural)
and keratin material are seen. F : The DSTdu has been removed. The DSTintradural is seen adhering to the lum. G : The caudal portion of the DST has
been completely removed via the L4L5 laminectomy. H and I : Operative exposure via a T12L1 laminectomy. (H) is the T12 side of the exposure; (I) the L1
side. A dermoid cyst along a slender DST (DSTrostral) is shown in (I). The DSTrotral was then cut at the yellow cross, and the cyst with the portion of DST
under the intact L2 and L3 laminae delivered from this exposure. The sub-millimeter thickness of the DST testies to the difficulty in detecting them
with MRI. J and K : Complete removal of the deep end of the DST from the dorsal midline of the spinal cord. Reused from Wong et al.
43)
with permission
from Springer Nature. MRI : magnetic resonance imaging.
A
D
H
B
E
I
C
F
J
G
K
Fig. 48.
Mid-sagittal MRI image
showing the post-operative appearance
of a skip laminectomy technique in
which T12 laminoplasty, L1 laminectomy,
and L4L5 laminectomy were done.
White arrowhead means laminoplasty
level. White stars mean intact laminae
level. Reused from Wong et al.
43)
with
permission from Springer Nature.
Focal Spinal Nondisjunction | Wong ST, et al.
177
J Korean Neurosurg Soc 64 (2) : 151-188
also urodynamic studies should be performed.
MRI is the imaging technique of choice to delineate the de-
tails of pathological anatomy of the malformation especially
regarding composite lesions. MRI f indings suggestive of
FSND are : 1) a tract linking the skin and the spinal cord even
it does not appear continuous (Figs. 4-6, 10); 2) posteriorly
tacked-up spinal cord (Figs. 10, 11, 13-15); and 3) a cystic lesion
over the dorsal midline (Figs. 7, 12, 17, 21-23). When FSND is
suspected on the MRI, the entire path of the tract must be
traced from the skin through subcutaneous tissue, lamina,
dura, and to the spinal cord. The constituents of the tract are
interpreted as much as possible (Fig. 45) : any cyst along its
course or in the vicinity is particularly noted (Figs. 7, 12, 17,
21-23), as is the presence of any associated anomalies especially
spinal cord lipoma and split cord malformation. Lastly, the
whole spinal axis should be surveyed for the rare coexistence
of multiple FSNDs in the same spine (Fig. 46).
However, the reliability of MRI in delineating FSNDs is far
from absolute. For example, a small tract can be below its res-
Fig. 49.
Intra-operative photographs showing complete excision of an intradural dermoid cyst via L2–L5 laminoplasties and S1 laminectomy (MRI
images are shown in Fig. 7). A and B : Surgical view after opening of dura. The dermoid cyst appears to merge with the conus and nerve roots. The
dermoid cyst communicates with the skin ostium via a dermal sinus tract at the S1 laminar level. C and D : Dissection to free the nerve roots from the
wall of the dermoid cyst. E : Excision cavity after complete excision of the dermoid cyst. Reused from Wong et al.
43)
with permission from Springer
Nature. MRI : magnetic resonance imaging.
A B
C D E
Dermoid cyst Dermoid cyst
Left sacral roots Nerveroots
Dermoid cyst
Dermoid cyst
Lef t lumbar roots
L2
level
S1
level
Conus
Conus
Fig. 50.
Six-year post-operative MRI images (of the patient shown in
Figs. 7 and 49) showing no recurrence of the dermoid cyst, and post-
laminoplasty changes. A : T2-weighted MRI. B : T1-weighted MRI with
gadolinium injection. Reused from Wong et al.
43)
with permission from
Springer Nature. MRI : magnetic resonance imaging.
A B
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olution (Fig. 5)12,38), and it cannot always differentiate a CSDST
from a LDM, except when the CSDST becomes inflamed and
exhibit abnormal enhancement of the tract, a constituent cyst,
and adjacent meninges (Fig. 4)4). All are essential information
for surgical planning.
MANAGEMENT
All FSNDs can cause functional impairment by tethering of
the spinal cord, while CSDST or any of its mixed forms pose
additional risks of inf lammation, infection, mass effect, and
even secondary hydrocephalus if left untreated. Early surgery
should be performed in all patients with CSDST, and in
symptomatic patients with LDM. In asymptomatic children
Fig. 52.
Exceedingly slender limited dorsal myeloschisis (LDM) stalk. A : Stalk attaches to discrete spot on dorsal cord surface. B :
En bloc
specimen
shows large complicated skin crater and the very slender LDM Stalk. Reused from Pang et al.
25)
with permission from Springer Nature.
A B
Fig. 51.
Surgical resection of a lumbar crater-type at (non-saccular) limited dorsal myeloschisis. A : Ellipse of resected skin crater and subcutaneous
tract going through defect in lumbodorsal fascia. B : Extradural stalk and dural stula. C : Intradural exposure showing stalk-cord union. D : Resection of
stalk ush with cord surface. E : Normal conus caudal to stalk attachment site. F :
En bloc
specimen showing, from right to left, skin ellipse bearing pale
epithelial crater, the subcutaneous portion bearing fat, the extradural portion of the stalk (between arrows), intradural stalk (between arrow and
arrowhead), and an exuberant cuff of tissue on the cord. Reused from Pang et al.
25)
with permission from Springer Nature.
A
D
B
E
C
F
Stalk
Stalk
Cord
Conus caudal to
stalk attachment
Focal Spinal Nondisjunction | Wong ST, et al.
179
J Korean Neurosurg Soc 64 (2) : 151-188
Fig. 53.
Moderate-sized limited dorsal myeloschisis stalk. A : Stalk has a ared-out cord attachment. B : Stalk resection leaves a sh-mouth shaped scar.
Reused from Pang et al.
25)
with permission from Springer Nature.
A B
Fig. 54.
Long limited dorsal myeloschisis stalk with vascular glomus (at
tip of forceps). Reused from Pang et al.
25)
with permission from Springer
Nature.
A B
Fig. 55.
Moderately thick limited dorsal myeloschisis (LDM) stalk with exuberant tentacles of blood vessels that seem to crawl on to the dorsal surface
of the spinal cord. A : Before LDM resection. B : After LDM stalk resection showing centripetal distribution of the blood vessels. Reused from Pang et al.
25)
with permission from Springer Nature.
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with pure LDM, we also strongly recommend surgery to obvi-
ate the dreadful consequences of late and unrecognized teth-
ering. Observation by serial MRI is probably only suitable for
patients with equivocal MRI f indings or perhaps in asymp-
tomatic adults.
For CSDST patients with active infection and neurological
deficits, urgent surgery covered with appropriate antibiotics
should be done. However, if infection is not accompanied by
Fi g. 57.
Crater type lumbar limited dorsal myeloschisis (LDM). A : Lumbar LDM stalk (arrows) with a very prominent hump (H) of abnormal tissues on the
cord. B : Resection at the base of this hump. C : Resection produced a very large scar (outlined by arrowheads). D : Dorsal pia-to-pia approximation of
scar with 8- O Nylon sutures. Reused from Pang et al.
25)
with permission from Springer Nature.
C D
A B
Neurulated LDM cut surface
Fig. 56.
Thick, complex-looking broneural stalk in a lumbar non-saccular LDM. A : Lesion contains dysplastic spinal cord tissue, large blood vessels,
ample skein of non-functioning nerves, and thickened folded membranes. Spinal cord is lif ted dorsally by the tethering effect. B : Bizarre arrangement
of dorsal roots (DR), and dorsal root entry zone (DREZ) surround a large at myeloschistic scar af ter stalk resection. Reused from Pang et al.
25)
with
permission from Springer Nature.
A B
DREZ DR
DR
Focal Spinal Nondisjunction | Wong ST, et al.
181
J Korean Neurosurg Soc 64 (2) : 151-188
neurological def icits, surgery should be deferred until the in-
fection has been treated with antibiotics and local therapy.
Surgery
The principles of surgery in all FSNDs are to completely un-
tether the spinal cord and to remove all epithelial elements if
present. For pure forms, a narrow laminectomy for exposure
is usually adequate. Laminoplasty is an option, and dural
grafting is rarely necessary. In cases with a large intradural
dermoid cyst, however, wider bony exposure is usually need-
ed. The extent of longitudinal exposure must include the span
between the skin lesion and where the tract joins the spinal
cord, which is usually apparent where the cord outline sud-
denly becomes trapezoid instead of the normal ovoid. In un-
certain cases, the skin should be widely draped to accommo-
date for extension of the incision. If the lesion is in the
lumbosacral region, the filum terminale may be thickened
and should be cut during treatment of the FSND, so that ap-
propriate provision must be made for more caudal exposure.
Surgical technique for CSDST
The patient is laid prone, the sinus ostium identified, and
the laminae of the planned laminectomy confirmed with ra-
Fig. 58.
Large cervical saccular limited dorsal myeloschisis. A : Exposure of the dorsal stula at the level of the nuchal fascial defect. B : The neck of the
sac passing through large laminar defect. C : The sac is opened from the top; basal neural nodule and the dural stula opening (into the cyst) are seen
through the cavity. D : Dural stula opened into the main thecal sac, showing the thin broneural stalk inserting on to the dorsal spinal cord. E : Stalk
being resected. All insets show exact level of the exposure. Reused from Pang et al.
25)
with permission from Springer Nature.
D E
A B C
Fig. 59.
Thoracic Saccular limited dorsal myeloschisis with the broneural
stalk (displayed by instrument) traversing the sac cavity and reaching the
dome of the sac. Reused from Pang et al.
25)
with permission from Springer
Nature.
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182 https://doi.org/10.3340/jkns.2020.0117
diograph (Fig. 47). Standard midline longitudinal skin inci-
sion with a small elliptical island around the ostium is made;
the tract is then traced from superficial to deep through the
subcutaneous layers and deep fascia, to reach the bifid spinous
process or through the interspinous ligament. The laminecto-
my is then carried out carefully around the tract. Dissection
of the tract should be done under magnification to minimize
the possibility of leaving behind residuum4). The dura should
Fig. 60.
Saccular limited dorsal myeloschisis (LDM) with the stalk-to-dome subtype of broneural stalk attachment. A : T
2
magnetic resonance imaging
shows slight tenting of the cord towards the sac on the sagittal image, and the broneural stalk (dome stalk) traversing the sac to the cord from the
base of the skin crater in the axial image. B : The sac with the slightly darker irregular skin at the lower dome with a slightly thinner covering (skin crater,
lower right) that may be thick squamous epithelium. The transilluminated picture (upper right) shows the small nubbin of (neural) tissue beneath the
skin crater, and the stream of bands traversing the middle of the sac. C : Shows the wide neck of the dural fistula at the base of the sac, and its
relationship with the cord dura. D : Sac opened from the top, showing the white area where the LDM stalk attaches to the cord surface. E : Close-up to
show the strands of the LDM stalk inser ting on the dorsal cord surface (upper). After resecting these strands (lower), the cord surface shows abnormal
clusters of wiggly blood vessels and scar tissue. Reused from Pang et al.
25)
with permission from Springer Nature.
A
C
E
D
B
Dome stalk Skin crater Skin crater
LDM stalk
LDM bed
Cord dura
LDM stalk
attachment
Dural stula
Focal Spinal Nondisjunction | Wong ST, et al.
183
J Korean Neurosurg Soc 64 (2) : 151-188
always be opened unless the surgeon is absolutely certain that
the tract ends outside the dura. When the tract goes intradu-
rally, a cuff of dura may need to be excised with the tract, and
the latter should be traced to its destination spot on the spinal
cord. Often the tract becomes attenuated and loosely perches
on the surface of the cord. Adequate bony exposure must be
done without compromise to display the full extent of the
tract. If a long tract truly spans many laminar levels, skip lam-
inectomy technique should be considered in which some lam-
inae between the tract’s dural entry point and its spinal cord
attachment point are strategically kept intact. The CSDST
tract can be carefully delivered from the laminectomy wounds
Fig. 61.
Lumbar saccular limited dorsal myeloschisis with segmental myelocystocoele. A : A long intradural stalk (S) picked up by micro-forceps. B : Stalk
traced to the hydromyelic portion of the cord after partial stalk resection. Reused from Pang et al.
25)
with permission from Springer Nature. C : conus.
A B
Fig. 62.
Intraoperative photos of the case shown in Fig. 19. A : A large skin-based sac with pearly epithelium, and hypertrichosis around the base of the
sac. B : The non-functional top of the cystocoele has been cut off leaving the functional base with nerve roots. C : Operative view looking through the
neck of the cystocoele into the hydromyelic cavity. D : After neurulation closure of the myelocystocoele neck.
A B
C D
Neurulation line
Rostr al cord
Rostral Cord
Conus
Conus
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Fig. 63.
Intra-operative photographs showing the excision of a LDM – lipoma complex (MRI images are shown in Fig. 45). A : The skin lesion, a cigar
burn crater with surrounding skin discoloration. B : Markings for the skin incision. C : Surgical exposure af ter L4–S2 laminectomies. D : The dura has been
opened. E : Surgical exposure after completion of
“
crotch dissection
”
. F : Detaching the stout LDM stalk and lipoma from the spinal cord. G : Residual fat
on the placode before nal trimming. H : Appearance of the spinal cord after neurulation. The nerve roots at the end of the spinal cord were stimulation
positive. Blue arrow means Extradural portion of the LDM. The patient has no neurological decits before and after the untethering surgery. Reused
from Wong et al.
43)
with permission from Springer Nature. LDM : limited dorsal myeloschisis, MRI : magnetic resonance imaging.
A B
C
E
G
D
F
H
Focal Spinal Nondisjunction | Wong ST, et al.
185
J Korean Neurosurg Soc 64 (2) : 151-188
(Fig. 48). Afterwards, primary closure of the dura is usually
possible.
The sinus tract may expand along its course or terminate in
a dermoid or epidermoid c yst. Extradurally located cysts are
readily excised. For large intradural cysts, refined microsurgi-
cal techniques are required for their complete removal since
the cyst wall is notoriously adherent to nerve roots and pia
(Figs. 49 and 50). Microbial cultures from adjacent areas
should be obtained, and post-operative antibiotics should be
given until negative growth is confirmed.
Surgical technique for at LDM
The surgical strategy for flat LDMs is similar to that for CS-
DST. After a standard midline skin incision, the skin crater or
pit is excised and the stalk at the base of the skin lesion is care-
fully dissected out and traced through the defects in myofas-
cial layers, and laminae or interspinous ligament (Fig. 51A). To
provide good exposure of the stalk-spinal cord attachment for
Fig. 64.
Post-operative MRI images of the patient shown in Fig. 63. A : T2-weighed sagittal MRI image showing a cord-sac ratio of 33%. B : T1-weighted
sagittal MRI image. C : Serial T2-weighted axial MRI images showing the spinal cord completely surrounded by cerebrospinal uid. Reused from Wong
et al.
43)
with permission from Springer Nature. MRI : magnetic resonance imaging.
A B C
Tab le 4 .
Pre-operative, 3-month post-operative, and 1 year post-operative neurological grades in LDM* patients grouped against LDM location
LDM location Pre-operative grade Post-operative grade
3 months 1 year
0 1 2 3 0 1 2 3 0 1 2 3
Cervical (n=11) 4 4 3 0 4 5 2 0 7 4 0 0
Thoracic upper (n=9) 2 6 1 0 3 6 0 0 6 3 0 0
Thoracic lower (n=7) 4 2 0 1 4 2 1 0 4 2 1 0
Thoracolumbar (n=8) 4 3 0 1 4 3 1 0 5 3 0 0
Lumbar (n=28) 15 83217 64120 701
Total number of patients (n=63) 29 23 7 4 31 22 8 1 41 19 1 1
Reused from Pang et al.25) with permission from Springer Nature. *Neurological grading system in LDM : grade 0, no decits or symptomsk; grade 1,
mild upper or lower extremity weakness, or pure sensory decits±pain; grade 2, moderate to severe upper or lower extremity weakness±sensory
decits, or neurogenic bladder without weakness; grade 3, upper or lower extremity weakness+neurogenic bladder. LDM : limited dorsal myeloschisis
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a safe excision, at least one level of laminectomy both rostral
and caudal to the stalk-spinal cord merge point should be
planned (Fig. 51B). Again, if the stalk spans multiple levels,
skip laminectomy may be considered.
A midline durotomy is made, centred upon the entry point
of the fibroneural stalk and extended according to the track of
the stalk as demonstrated on the MRI. The usually slender
stalk is most often attached to a discrete linear spot or cleft on
the dorsal midline of the cord (Fig. 51C); it is simply cut flush
with the cord surface (Fig. 51D and E). Any peripheral nerve
twigs, blood vessels, and fibrous bands encircling the neural
stalk are similarly cut. Once the intradural stalk had been dis-
connected from the cord, the entire stalk with its skin ap-
pendage is resected en bloc (Fig. 51F).
The LDM stalk may be exceedingly slender and attaches to
the cord in a minute midline scar (Fig. 52), or the stalk flares
out into a wider hold on the cord so that the cut edge on the
cord resembles a gaping fish mouth (Fig. 53). The stalk may
also contain a glomus of vascular channels (Fig. 54), or its
deep end expands into tentacles of blood vessels that crawl on
the cord (Fig. 55). Rarely, the stalk attachment is stout and de-
ceptively complex, and the dorsal roots surround it like a cuff
(Fig. 56). These attachments are cut f lush as above but sparing
the surrounding nerve root to reveal a large base of raw spinal
cord (Fig. 56B). Rarely, it is necessary to approximate the pial
edges of the large raw bed of a pure LDM to eliminate a poten-
tially adherent surface susceptible to re-tethering (Fig. 57). The
dura is closed primarily.
Surgical technique for saccular LDMs
The surgical technique for tackling the internal structures
of LDMs is basically the same whether the LDM is saccular or
flat. The minor differences between handling the two types
lay in the initial superficial soft tissue dissection. For the sac-
cular LDMs, a large skin ellipse is made at the sessile base of
the sac to expose the dural funnel where the narrow dural fis-
tula fans out to form the sac at the skin level (Fig. 58A). The
dural fistula is then traced to the lamina level as with the f lat
LDM (Fig. 58B).
For the basal nodule type of saccular LDM, the sac is en-
tered at the base to locate the basal neural nodule (Fig. 58C)
and the underlying fibroneural stalk within the dural fistula,
where it is traced to its attachment to the cord and removed
(Fig. 58D and E). Saccular LDMs with very thick stalks that
traverse the sac to reach the dome are exposed from the spinal
cord side up towards the top (Fig. 59). The base of the stalk is
then disconnected from the cord surface. In large saccular le-
sions with slender stalks that may be hard to find, the sac is
opened at the dome and the fibroneural stalk is located at the
base of the abnormal skin crater, then traced to the spinal cord
surface where it is transected (Fig. 60). In saccular LDM with
myelocystocoeles, the stalk may be longer than expected and
its cut end can often be traced directly into the hydromyelic
cavity of the cord (Figs. 61 and 62).
Surgical techniques for FSNDs associated with other anomalies
The operative strategy for these conditions is a combination of
the above techniques for FSNDs with the specific techniques
suitable for the associated malformations2 5,26). The technique
for the associated malformation usually predominates (Figs.
63 and 64). The most salient point to note is the essential total
extirpation of any dermal elements in a complex lesion.
OUTCOMES AND CONCLUSION
The clinical outcome of FSNDs is dictated by the presenta-
tion clinical status. With proper surgical techniques, surgery
for FSNDs without large intradural dermoid/epidermoid cysts
is usually uncomplicated; recurrence of dermal elements and
re-tethering should be extremely rare; and most FSND pa-
tients without neurological def icits remain neurologically in-
tact af ter surgery1,25 ,42). Over two thirds of patients with pre-
operative neurological deficits improve after surgery; about
one third will not improve though remain stable (Table
4)1,2 5, 41). In CSDST patients with large intradural dermoid/epi-
dermoid cysts or active infections, the results are less salubri-
ous1,7, 40 ,4 3). These statistics thus highlight the importance of
early detection and prompt surgical intervention in FSNDs.
CONFLICTS OF INTEREST
No potential conf lict of interest relevant to this article was
reported.
Focal Spinal Nondisjunction | Wong ST, et al.
187
J Korean Neurosurg Soc 64 (2) : 151-188
INFORMED CONSENT
This type of study does not require informed consent.
AUTHOR CONTRIBUTIONS
Conceptualization : D P, ST W
Data curation : DP, S TW
Formal analysis : STW
Funding acquisition : DP
Methodology : DP, ST W
Project administration : STW
Visualization : STW
Writing - original draft : STW
Writing - review & editing : DP
ORCID
Sui-To Wong https://orcid.org/0000-0001-7940-8866
Dachling Pang https://orcid.org/0000-0002-6 603-6546
References
1. Ackerman LL, Menezes AH : Spinal congenital dermal sinuses: a 30-year
experience. Pediatrics 112(3 Pt 1) : 641-647, 2003
2. Colas JF, Schoenwolf GC : Towards a cellular and molecular understand-
ing of neurulation. Dev Dyn 221 : 117-145 , 2 001
3. Cornips EM, Weber JW, Vles JS, van Aalst J : Pseudo-dermal sinus tract
or spinal dermal-sinus-like stalk? Childs Nerv Syst 27 : 118 9 -1193 ,
2011
4. De Vloo P, Lagae L, Sciot R, Demaerel P, van Loon J, Van Calenbergh F :
Spinal dermal sinuses and dermal sinus-like stalks analysis of 14 cases
with suggestions for embryologic mechanisms resulting in dermal sinus-
like stalks. Eur J Paediatr Neurol 17 : 575 -584, 2013
5. Eibach S, Moes G, Zovickian J, Pang D : Limited dorsal myeloschisis as-
sociated with dermoid elements. Childs Nerv Syst 33 : 55-67, 2017
6. Elton S, Oakes WJ : Dermal sinus tracts of the spine. Neurosurg Focus
10 : e4, 2001
7. Girishan S, Rajshekhar V : Rapid-onset paraparesis and quadriparesis in
patients with intramedullary spinal dermoid cysts: report of 10 cases. J
Neurosurg Pediatr 17 : 86-93, 2016
8. Hiraoka A, Morioka T, Murakami N, Suzuki SO, Mizoguchi M : Limited
dorsal myeloschisis with no extradural stalk linking to a flat skin lesion:
a case report. Childs Nerv Syst 34 : 2497-2501, 2018
9. Kim JW, Wang KC, Chong S, Kim SK, Lee JY : Limited dorsal myeloschi-
sis: reconsideration of its embryological origin. Neurosurgery 86 : 93-
100, 2020
10. Lee JY, Chong S, Choi YH, Phi JH, Cheon JE, Kim SK, et al. : Modification
of surgical procedure for “probable” limited dorsal myeloschisis. J Neu-
rosurg Pediatr 19 : 616-619, 2017
11. Lee JY, Park SH, Chong S, Phi JH, Kim SK, Cho BK, et al. : Congenital
dermal sinus and limited dorsal myeloschisis:”spectrum disorders” of
incomplete dysjuction between cutaneous and neural ectoderms. Neu-
rosurgery 84 : 428 -434, 2019
12. Lee SM, Cheon JE, Choi YH, Kim IO, Kim WS, Cho HH, et al. : Limited
dorsal myeloschisis and congenital dermal sinus: comparison of clinical
and MR imaging features. AJNR Am J Neuroradiol 38 : 176-182,
2017
13. Martínez-Lage JF, Almagro MJ, Ferri-Ñiguez B, Izura Azanza V, Serrano C,
Domenech E : Spinal dermal sinus and pseudo-dermal sinus tracts: two
different entities. Childs Nerv Syst 27 : 609-616, 2011
14. Martins-Green M : Origin of the dorsal surface of the neural tube by
progressive delamination of epidermal ectoderm and neuroepithelium:
implications for neurulation and neural tube defects. Development
103 : 687-70 6, 198 8
15. Martins-Green M, Erickson CA : Basal lamina is not a barrier to neural
crest cell emigration: documentation by TEM and by immunofluorescent
and immunogold labelling. Development 101 : 517-533, 1987
16. Morioka T, Suzuki SO, Murakami N, Mukae N, Shimogawa T, Haruyama
H, et al. : Surgical histopathology of limited dorsal myeloschisis with flat
skin lesion. Childs Ner v Syst 35 : 119-128 , 2019
17. Morioka T, Suzuki SO, Murakami N, Shimogawa T, Mukae N, Inoha S,
et al. : Neurosurgical pathology of limited dorsal myeloschisis. Childs
Nerv Syst 34 : 293-303, 2018
18. Müller F, O’Rahilly R : The prechordal plate, the rostral end of the no-
tochord and nearby median features in staged human embryos. Cells
Tissues Organs 173 : 1-20, 2003
19. Müller F, O’Rahilly R : The primitive streak, the caudal eminence and re-
lated structures in staged human embryos. Cells Tissues Organs 177 :
2-20, 2004
20. Nikolopoulou E, Galea GL, Rolo A, Greene ND, Copp AJ : Neural tube
closure: cellular, molecular and biomechanical mechanisms. Develop-
ment 144 : 552-566 , 2017
21. Pang D : Surgical management of spinal dysraphism in Fessler R, Sekhar
L (eds) : Atlas of Neurosurgical Techniques. New York : Thieme
Medical and Scientific Publishers, 2006, pp729-758
22. Pang D, Dias MS : Cervical myelomeningoceles. Neurosurgery 33 :
363-373, 1993
23. Pang D, Dias MS, Ahab-Barmada M : Split cord malformation part I: a
unified theory of embryogenesis for double spinal cord malformations.
Neurosurgery 31 : 451-480, 1992
24. Pang D, Zovickian J, Oviedo A, Moes GS : Limited dorsal myeloschisis: a
distinctive clinicopathological entity. Neurosurgery 67 : 1555-1580 ,
2010
25. Pang D, Zovickian J, Wong ST, Hou YJ, Moes GS : Limited dorsal myelos-
J Korean Neurosurg Soc 64 | March 2021
188 https://doi.org/10.3340/ jkns.2020.0117
chisis: a not-so-rare form of primary neurulation defect. Childs Nerv
Syst 29 : 1459-148 4, 2013
26. Pang D, Zovickian J, Wong ST, Hou YJ, Moes GS : Surgical treatment of
complex spinal cord lipomas. Childs Nerv Syst 29 : 14 85-1513, 2013
27. Quon JL, Grant GA : Commentary: limited dorsal myeloschisis: reconsid-
eration of its embryological origin. Neurosurgery 86 : E13- E14, 2 020
28. Rolo A, Escuin S, Greene NDE, Copp AJ : Rho GTPases in mammalian
spinal neural tube closure. Small GTPases 9 : 283-289, 2018
29. Rossi A, Piatelli G, Gandolfo C, Pavanello M, Hoffmann C, Van Goethem
JW, et al. : Spectrum of nonterminal myelocystoceles. Neurosurgery
58 : 509-515, 2006
30. Schoenwolf GC : Observations on closure of the neuropores in the chick
embryo. Am J A nat 155 : 445-465, 1979
31. Schoenwolf GC, Smith JL : Mechanisms of neurulation: traditional view-
point and recent advances. Development 109 : 243-270, 19 90
32. Selleck MA, Bronner-Fraser M : Origins of the avian neural crest: the role
of neural plate-epidermal interactions. Development 121 : 525-538,
1995
33. Silver MH, Kerns JM : Ultrastructure of neural fold fusion in chick em-
bryos. Scanning Electron Microscope 2 : 209-216, 1978
34. Steinbok P : Dysraphic lesions of the cervical spinal cord. Neurosurg
Clin N Am 6 : 367-376, 1995
35. Steinbok P, Cochrane DD : The nature of congenital posterior cervical or
cervicothoracic midline cutaneous mass lesions: report of eight cases. J
Neurosurg 75 : 206 -212, 19 91
36. Suneson A, Kalimo H : Myelocystocele with cerebellar heterotopia. J
Neurosurg 51 : 392-396, 1979
37. Theveneau E, Mayor R : Neural crest delamination and migration: from
epithelium-to-mesenchyme transition to collective cell migration. Dev
Biol 366 : 34 -54 , 2012
38. Tisdall MM, Hayward RD, Thompson DN : Congenital spinal dermal
tract: how accurate is clinical and radiological evaluation? J Neurosurg
Pediatr 15 : 651-656, 2015
39. van Aalst J, Beuls EA, Cornips EM, van Straaten HW, Boselie AFM, Rijk-
ers K, et al. : The spinal dermal-sinus-like stalk. Childs Nerv Syst 25 :
191-197, 2009
40. van Aalst J, Beuls EA, Cornips EM, Vanormelingen L, Vandersteen M,
Weber JW, et al. : Anatomy and surgery of the infected dermal sinus of
the lower spine. Childs Nerv Syst 22 : 13 07-1315, 2 006
41. van Straaten HW, Jaskoll T, Rousseau AM, Terwindt-Rouwenhorst EA,
Greenberg G, Shankar K, et al. : Raphe of the posterior neural tube in
the chick embryo: its closure and reopening as studied in living embryos
with a high definition light microscope. Dev Dyn 198 : 65-76, 1993
42. Wang KC, Yang HJ, Oh CW, Kim HJ, Cho BK : Spinal congenital dermal
sinus--experience of 5 cases over a period of 10 years. J Korean Med
Sci 8 : 341-347, 1993
43. Wong ST, Kan A, Pang D : Limited dorsal spinal nondisjunctional disor-
ders: Limited dorsal myeloschisis, congenital spinal dermal sinus tract,
and mixed lesions in Di Rocco C, Pang D, Rutka JT (eds) : Textbook of
Pediatric Neurosurgery, ed 1. Switzerland : Springer, 2020
44. Yamaguchi Y, Shinotsuka N, Nonomura K, Takemoto K, Kuida K, Yosida
H, et al. : Live imaging of apoptosis in a novel transgenic mouse high-
lights its role in neural tube closure. J Cell Biol 195 : 1047-1060, 2011
