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Limited Dorsal Spinal Nondisjunctional Disorders: Limited Dorsal Myeloschisis, Congenital Spinal Dermal Sinus Tract, and Mixed Lesions

  • Sui-To WongEmail author
  • Amanda Kan
  • Dachling PangEmail author
Living reference work entry

Abstract

Spinal dysraphic lesions due to incomplete fusion and consequent failed disjunction of a limited segment of the dorsal neural tube during primary neurulation are the subjects of this chapter. We use the term “limited dorsal spinal nondisjunctional disorders” (LDSNDs) to encompass several known varieties of such lesions, namely, limited dorsal myeloschisis (LDM), congenital spinal dermal sinus tract (CSDST), mixed lesions of the two, and other closely related complex lesions (Wang et al. 1993; Pang et al. 2013a; Eibach et al. 2017). All of these probably share a common embryogenetic mechanism and similar clinical manifestations.

Introduction

Spinal dysraphic lesions due to incomplete fusion and consequent failed disjunction of a limited segment of the dorsal neural tube during primary neurulation are the subjects of this chapter. We use the term “limited dorsal spinal nondisjunctional disorders” (LDSNDs) to encompass several known varieties of such lesions, namely, limited dorsal myeloschisis (LDM), congenital spinal dermal sinus tract (CSDST), mixed lesions of the two, and other closely related complex lesions (Wang et al. 1993; Pang et al. 2013a; Eibach et al. 2017). All of these probably share a common embryogenetic mechanism and similar clinical manifestations.

Congenital spinal dermal sinus tract has been a well-recognized entity for many decades. Moise first described a case in 1926, Walker and Bucy coined the term in 1934, and Mason devoted a chapter to it in the first textbook of pediatric neurosurgery published in 1959 (Matson 1959; Wang et al. 1993). There are more than 10 case series of CSDST published since 1993 focusing on different clinical perspectives (Table 1) (Wang et al. 1993; Elton and Oakes 2001; Jindal and Mahapatra 2001; Ackerman and Menezes 2003; Lee 2005; van Aalst et al. 2006; Radmanesh et al. 2010; Martínez-Lage et al. 2011; De Vloo et al. 2013; Mete et al. 2014; Singh et al. 2015; Tisdall et al. 2015; Girishan and Rajshekhar 2016; Venkatesh et al. 2018). It is known to be associated with other anomalies especially split cord malformations and spinal cord lipomas.
Table 1

Clinical series of congenital spinal dermal sinus tracts

 

Year of publication; author;

Place;

Data period

Terminology

No. of cases

Agea

Location in lumbosacral region

Intradural involvement

Presentation

, %, (cases)

Skin stigmata

, %, (cases)

Infection

Associated anomalies (cases)

Remarks

1

2018; Venkatesh et al.,

Tamil Nadu, India;

2006–2008

Spinal dermal sinus

10

1.5–27 (median, 5.5)

60%

100%

Skin stigmata 60%.

Neurological deficits 40% (B&B (1), B&B + LW (3))

All had ostium.

Hair 40%.

Inflamed skin 10%

NA

NC (1),

SCL (2)

 

2

2016;

Girishan et al.;

Vellore, India;

2000–2014

Intramedullary spinal dermoid cyst

10

9 cases:

8 m–2

(median, 1)

1 case:

25

78%

100% (a selected group)

Rapid onset LW 100%

All 9 pediatric had ostium.

1 adult had no ostium.

Meningitis 20%

Sinus discharge 70%

NA

In a series of 50 dermal sinus patients

3

2015;

Singh et al.;

Haryana, India;

2007–2013

Spinal dorsal dermal sinus tract

21

9 m–15 (mean 8.2)

67%

Not specified

EC 10%,

DC 38%

Neurological deficits 100%

All had ostium

Associated skin stigmata, (15) (most pigmentation)

Meningitis

14%

SCL (2),

SCM (6)

 

4

2015;

Tisdall et al.;

London,

UK;

1998–2010

Congenital spinal dermal tract

74

1 week–16 (mean 2.5)

97%

86%.

Intraspinal DC 24%

Skin stigmata 58%.

B&B 7%

Either:

Ostium/punctum 81%,

(some from S2-S5).

Cigar burn 19%

Associated with:

Hair 20%Hemangioma 28%.

Skin tag 8%.

Subcutaneous lipoma 11%

Meningitis 7%.

Local infection 14%.

Sinus discharge 20%

NA

 

5

2014;

Mete et al.;

Turkey;

1994–2010

Congenital dermal sinus tract of the spine

16

10 d–36 (mean 10)

63%

63%

Neurological deficits 25% (B&B 12.5%, LW 12.5%)

Ostium 25%. Lumbar dimple 31%

Hair 31%

Pigmentation 19%

Subcutaneous lipomas 16%

NA

SCL (1),

SCM (1)

 

6

2013;

De Vloo et al.;

Belgium;

1996–2012

Spinal dermal sinus

5

1–32 m (mean 2 m)

100%

Probably 100% (at most 1 ended at dura)

Skin stigmata 60%

Infection 40%

Ostium 60% (all had lumen with histology)

Skin tag 40%

Hair 20%

Haemangioma 20%. Subcutaneous lipomas 20%

Meningitis 40%

SCL 20%

Dermal-sinus-like stalk: 9 cases

7

2011;

Martinez-Lage et al.;

Spain;

1980–2010

Spinal dermal sinus

8

2 m–4.6 (mean 19 m)

75%

75%

(and 25% dural)

Skin stigmata 100%.

Neurological deficits 50%.

Infection 63%

Ostium 100%

NA

NA

Discussion on pseudo-dermal sinus tract:12 cases

8

2010;

Radmanesh et al.;

Iran;

2001–2008

Dermal sinus tract of the spine

35

3d–8.4 (median 1.1)

97%

(include some sacral)

46.2%

Skin stigmata 57%

Infection 31%.

Neurological deficits 37% (B&B 14%, LW 23%)

All had ostium. Associated with:

Hair 17%. Pigmentation 20%

Haemangioma 14%

Subcutaneous lipomas 9%

Skin tag 3.

Meningitis 23%.

Skin inflamed 23%

SCL 14%.

SCM 14%.

 

9

2006;

van Aalst et al.;

Netherlands;

NA

Infected dermal sinus of the lower spine

4

1–21 m (mean 9 m)

100%

100%

Infection 100%

All had ostium.

Hair 25%

Meningitis 100%.

Sinus discharge 25%

NA

 

10

2005;

Lee et al.;

Seoul,

Korea;

1986–2003

Congenital dermal sinus

13

2 m–13y (median 2.2)

69%

69%

NA

All had ostium

NS

SCL 31%.

SCM 8%

Also 7 occipital DST

11

2003;

Ackerman et al.;

Iowa, US;

1970–2003

Spinal congenital dermal sinus

28

1d–55

(16 cases <=1)

64%

79% had tethered cord

Skin stigmata 54%

Neurological deficits 29% (68% on exam)

Foot deformity 14%

Infection 11%. Pain 7%. Scoliosis 4%

Ostium, hair, haemangioma, pigmentation, subcutaneous lipomas, skin tag; % NA

Meningitis 4%

Skin infection 7%

Sinus discharge 4%

NC 1

SCL 8

SCM 3

 

12

2001;

Elton et al.; Alabama, US;

1981–2000

Dermal sinus tracts of the spine

23

5 d–38 (mean 6.6)

NA

NA.

Intradural DC 26%

NA

NA

NA

SCL 2

SCM 3

 

13

2001;

Jindal et al.;

New Delhi, India;

7 years

Spinal congenital dermal sinus

23

(mean 10.2)

87%

NA

Neurological deficits 87% (LW 87%, B&B 52%)

Skin stigmata 13%

NA

NA

SCM 6.

 

14

1993,

Wang et al.;

Seoul, Korea;

1982–1992

Spinal congenital dermal sinus

5

1 m–24 (median 3)

60%

100%

Intradural EC/DC 40%

Skin 20%

LW 40%

Pain 40%

All had ostium.

Hair 40%

Haemangioma 40%

Meningitis 40%

Teratoma 20%

 

B&B bowel and bladder incontinence, LW limb weakness, NC neurenteric cyst, SCL spinal cord lipomas, SCM split cord malformation, EC epidermoid cyst, DC dermoid cyst, NA data not available

aIn years unless specified, m = month, d = days

In contrast, LDM is a more recently defined entity. The senior author (DP) first used the term in 1992 while describing lesions associated with split cord malformations, again in 1993 to designate a cystic form of cervical dysraphic malformation, then finally published a comprehensive report on this entity in 2010 (Pang et al. 1992; Pang and Dias 1993; Pang et al. 2010). In it, the relationships between LDM and other congenital anomalies such as spinal cord lipomas, split cord malformations, and meningocele manque are discussed in detail. It has since become apparent that other dorsal spinal cord tethering lesions rather imprecisely called “nonepithelial long tethering tract”, “dermal-sinus-like stalk,” and “pseudo-dermal sinus tract,” described between 2007 and 2013, are in fact variant forms of LDM (Rajpal et al. 2007; van Aalst et al. 2009; Cornips et al. 2011; Martínez-Lage et al. 2011; De Vloo et al. 2013). Finally, since 2013, there have been reports of mixed forms of LDM with CSDST, and LDM with dermal elements (Pang et al. 2013a; Eibach et al. 2017; Lee et al. 2018).

In a related note, congenital dermal sinus unrelated to primary neurulation failure can occur in the lower sacral and coccygeal region. They are mostly the so-called simple sacral dimples and coccygeal sinuses or pits, whose internal parts only extend to the deep fascia and not beyond, thus are of little neurosurgical concern (Weprin and Oakes 2000; Elton and Oakes 2001).

Embryogenetic Mechanisms

Normal Primary Neurulation

Primary neurulation, the formation of the primary neural tube – the primordium of the brain and the spinal cord down to the S1 level – consists of four main stages occurring sequentially at each axial level of the embryo. They are: (1) Formation of the neural plate, (2) shaping of the neural plate, (3) bending of the neural plate, and (4) closure of the neural groove (Colas and Schoenwolf 2001).

Closure of the neural groove starts at the hindbrain/upper cervical region in humans and propagates both rostrally and caudally (Colas and Schoenwolf 2001). During this stage, fusion of the neural folds and complete separation of surface epithelium (SE) from neuroepithelium (NE) take place at the dorsal midline. It consists of a complex sequence of events at the tissue level which occur in an overlapping manner that cannot be unlinked from the preceding stages, i.e., bending of the neural plate, formation of the paired neural folds, and their convergence towards the dorsal midline (Martins-Green 1988; Schoenwolf and Smith 1990; van Straaten et al. 1993; Colas and Schoenwolf 2001).

The sequence of events are as follows (Fig. 1) (Martins-Green 1988; Schoenwolf and Smith 1990; van Straaten et al. 1993 and 1996; Colas and Schoenwolf 2001): (1) The formation of an overlapping SE and NE junction: When the neural plate is first formed, NE cells and SE cells lie side by side on the same plane at the border of the neural plate. As the paired neural folds progressively elevate and converge towards the dorsal midline, the NE cells enlarge in height and drag the flattened SE cells onto their dorsal surface. In effect, the two epithelia are connected over a broad, overlapping surface of several cells’ thickness. (2) Delamination: An interepithelial space then gradually develops in the middle part of this broad interface of the two epithelia. The basal lamina of the two epithelia however remains continuous at the ventral point (ventro-lateral extreme of their contact). Thus, when the interepithelial space expands, it acquires a crescent shape. As the two neural folds approach each other to close the dorsal midline gap, the interepithelial space extends further dorsally towards the dorsal midline. The basal lamina bridge at the ventral contact point of the two epithelia also gradually breaks down, and the two epithelia become separate ventrally. A new basal lamina then forms on the “interepithelial surfaces” of the two epithelia. When the interepithelial space reaches the dorsal-most meeting point of the two epithelia, the epithelia separate completely, thereby consummating the process known as disjunction. (3) Fusion at the dorsal midline: Fusion of the SE and NE layers with their respective counterpart on the opposite side of the midline takes place simultaneous with delamination/disjunction. Fusion is preceded by apposition of the two opposing sets of epithelia at the tips of the two neural folds, followed by intercellular adhesion at points of contact. The initial contact areas are often discontinuous from superficial to deep (Silver and Kerns 1978), and it is likely that fusion of the two epithelial layers proceeds independently of each other (van Straaten et al. 1993). Schoenwolf, using chick embryos in 1982, concluded that fusion completed first in the SE (Schoenwolf 1982). However, van Straaten in 1993, also using chick embryos, demonstrated that there was no fixed priority of completion of fusion in the two layers (van Straaten et al. 1993).
Fig. 1

Normal primary 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 final phase in closure of the neural groove. (d) Closed neural tube at an axial level. en endoderm, n notochord, NE neuroepithelium, SE surface epithelium

It is obvious that the final steps of delamination (disjunction) and fusion of the two epithelia are topographically and chronologically closely related, but the fine details of their interrelationship are still not fully elucidated. What is well established is that in normal embryos, complete closure of the neural groove at any axial level is marked by the presence of a continuous basal lamina under the SE across the dorsal midline and a continuous sheath of basal lamina around the NE (primary neural tube) at that level (Martins-Green and Erickson 1987). It is possible that fusion of the epithelia at the dorsal midline and their delamination/disjunction are independent of each other, but intuitively, fusion of the epithelia must occur before final delamination (disjunction) of the SE and NE. The answer may have to rely on dynamic observation at the ultrastructural level.

Pathoembryogenesis of Limited Dorsal Spinal Nondisjunctional Disorders

Given the intricate cellular events in the final phases of neural groove closure, faults may occur at a focal dorsal point of the developing primary neural tube to give rise to failed or incomplete fusion and nondisjunction of a small, focal, or “limited,” segment anywhere along the future spinal cord as caudal as the S1 cord level.

A LDSND differs from the exposed, totally flat, and unclosed neural placode of an open myelomeningocoele only in the degree of incompleteness of neurulation (Pang 2006). In LDSNDs, most of the steps of primary neurulation including elevation, in-folding, and recognition of the dorsal neural folds have occurred except for the final phase. The basic configuration of the neural tube has taken shape, except for a thin slip in the dorsal midline. Several anatomical phenotypes are seen in the final malformation, depending on the aberrant behaviors of the different primordial cells involved in the three key component steps of neural groove closure, i.e., delamination/disjunction of the two epithelia, fusion of the SE, and fusion of the NE. Thus, individual or combined errors of the primordial SE and NE cells, mesoderm and neural crest cells will ultimately determine the matured features of the subtype malformations under the aegis of LDSND (Fig. 2) (Schoenwolf and Smith 1990; Selleck and Bronner-Fraser 1995; Theveneau and Mayor 2012).
Fig. 2

Proposed embryogenetic mechanisms for different types of limited dorsal spinal nondisjunctional disorders. (a) Congenital spinal dermal sinus tract (CSDST). (b) Limited dorsal myeloschisis (LDM). (c) Mixed CSDST and LDM – regular type. (d) Mixed LDM and dermal elements – irregular type. NE neuroepithelium, SE surface epithelium

The embryogenetic mechanisms for the subtype LDSND malformations are as follows:
  1. 1.

    CSDST: When the SE fails to fuse at a focal point, but the underlying NE has acquired intercellular adhesions across the dorsal midline, and disjunction does not occur, a CSDST develops. In this situation, closure of the primary neural tube is unhindered, but because local disjunction never happens, the gapping SE is persistently linked with the NE in a very focal area. The midline gap between the converging SE and dorsal scleromyotomes from opposite sides of the embryo remains very narrow. Further unimpeded development of the otherwise normal full-thickness dorsal myofascial tissues around the midline strip progressively sets the primary neural tube away from the surface and deeper into the body, where it ultimately assumes its primarily intraspinal location. A dorsal median tract of SE tissue, however, retains as the original link between the closed neural tube and the still slightly gaping surface. Anchorage of the tract on the SE side is firm because its component cells are still essentially part of the surface epithelium, but its deep end may not be firmly attached to the NE cells after closure of the neural groove. Cellular movements during normal development of the scleromesoderm, meninges, and neural crest cells could have dislodged the tract from the underlying neural tube, 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. 2.

    LDM: When the NE fails to fuse at a focal point but the overlying SE has acquired intercellular adhesions across the dorsal midline, full disjunction also does not occur. Similar to the preceding situation but in reverse, the SE gap is closed, but because local NE fusion and disjunction never happen, the NE is persistently linked with the SE in this very focal area; the midline gap between the converging NE and dorsal scleromyotomes from opposite sides of the embryo remains very narrow. Further unimpeded development of the otherwise normal full-thickness dorsal myofascial tissues around the midline strip progressively sets the neural tube away from the surface and deeper into the body, where it ultimately assumes its primarily intraspinal location. A dorsal median tract of NE tissue (versus SE tissue in CSDST), however, retains as the original link between the focally gapping neural tube and the closed SE (Pang et al. 2010). The anchorage of the tract on the undersurface of the SE affects the integration of mesodermal tissue to form normal skin at that focal area.

     
  3. 3.

    Mixed LDM and CSDST: When both the SE and NE fail to fuse and disjunction does not occur, a midline tract as in the above two entities develops, but the inner portion of the tract consists of NE tissue while the outer tract contains mainly SE. The relative proportion of the two kinds of tissues depends on the “pulling forces” during embryogenesis. Mixed LDM and dermal sinus tracts are rare but may easily elude detection (Lee et al. 2018; Eibach et al. 2017).

     
  4. 4.

    LDM with scattered dermal element: As for those LDMs with dermal elements, but without a sinus tract, the origin of the dermal elements could be from pluripotent cells near the midline surface, or from SE cells somehow included in the LDM stalk during its ventral movement (Pang et al. 2013a; Eibach et al. 2017).

     
  5. 5.

    LDSND with spinal cord lipoma: LDMs have been known to be associated with dorsal lipomas, either directly adjacent to the lipoma stalk or continuous with it. Since both dorsal and transitional lipomas are thought to arise from premature disjunction due to faulty end-stage neural groove closure, it is not surprising that nondisjunction disorders may coexist (Pang et al. 2013a). Equivalent parallel defects may also explain the coexistence of lipomas and CSDST.

     
  6. 6.

    LDSND with split cord malformation: It is conceivable that the fibroneural stalk or sinus tract found in some cases of split cord malformation are in fact the persistent dorsal remnant of an anomalous ecto-endodermal fistula formed during early gastrulation (Pang et al. 1992; Pang 2006).

     

Morbid Anatomy and Clinical Manifestations of Limited Dorsal Spinal Nondisjunctonal Disorders

The hallmark of a LDSND is the presence of a tract linking the spinal cord at or above the S1 spinal cord level to the dorsal midline skin. Variations in the exact histological architecture explain the spectrum of nondisjunctional entities, and partial atresia of the tract may account for certain variants of the full forms (Hiraoka et al. 2018). For purposes of archiving, the “level” of a LDSND should be the same level of the laminar defect the fibroneural stalk passes through, which likewise localizes to the corresponding spinal cord level where the initial nondisjunctional error occurred.

Pure CSDST

Morbid Anatomy

The essential feature of a CSDST is the presence of a dorsal midline sinus tract – a hollow tubular structure lined by squamous epithelium (van Aalst et al. 2009; Martínez-Lage et al. 2011). It is the direct derivative of the SE nonfusion defect. The size of the surface opening (ostium) of this tract is variable but usually small (Fig. 3). It always leads to a deeper part of unpredictable length (Figs. 4, 5, and 6). Over 60% end intradurally and some can be firmly adherent to the spinal cord (Table 1).
Fig. 3

(a) Dermal sinus ostium, appeared as a pin-point area of dry scaling with surrounding red discoloration, but without soft tissue swelling. (b) Magnified 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) Magnified view of c

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, 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 (arrow head). (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

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 (arrow heads), and vaguely the L1/L2 nodule are demonstrable by MRI. Left panel: T2-weighted MRI image with cut lines numbered 1–16. 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, d). There is a two 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. Arrow heads = the subcutaneous portion of the dermal sinus tract

Over 60% of CSDSTs are located in the lumbosacral region, the rest are scattered in the cervical and thoracic regions (Table 1). Because the spinal cord ascends for a fair distance along the vertebral column during the perinatal and early postnatal periods due to their discrepant growth rates, the shape of the sinus tract also varies depending on its level of origin. A lumbosacral sinus takes on a V- shape with the apex pointing at exactly the laminar level of its embryologic error and from thence the tract ascends towards the dura. The subcutaneous tract becomes progressively more horizontal with higher lesions until it points upwards towards the dura in cervico-thoracic lesions. At the skin level, the sinus ostium is sometimes accompanied by other skin stigmata (Fig. 3). At the laminar level, the tract may go through a bifid spinous process or lamina, or through the interspinous ligament. It then enters the dura but can also travel between the dural sleeves for a short distance before becoming intradural. Within the thecal sac, it may be adherent to the filum or nerve roots and, as a rule, one should assume all sinus tracts reach the spinal cord until proven otherwise. Anywhere along the sinus tract, existing keratin material may develop a dermoid cyst, which can be intramedullary (Fig. 7). In a report of 10 spinal intramedullary dermoid cysts, 9 had a traceable CSDST (Girishan and Rajshekhar 2016). The rare absence of a CSDST in these cases is probably due to atresia of the outer tract or isolated sequestration of pluripotent SE cells (Hiraoka et al. 2018).
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 inflammation. The intradural dermoid cyst communicates with an outside dermal sinus tract at the caudal aspect of the S1 laminae (white arrow head in e)

Histologically, a CSDST is lined by keratinizing stratified squamous epithelium (Fig. 8). Hair shafts and follicles are present in variable abundance. Mesenchymal derivatives including blood vessels and fibrous tissue are seen in the periphery (Figs. 8 and 9). Occasionally, nerve fibers are present. The lumen of the tract and cavity within dermoid cysts are filled with keratin material (Fig. 10). In some cases, a lumen may only be patent in part of the tract (Fig. 9). In slender tracts, a transitional zone of epithelial to nonepithelial tissues near the tract’s inner end can be observed (Fig. 11). Because of the communication with the skin surface, open sinus tracts are prone to bacterial infections and chemically induced inflammation from keratin accumulation. Thus inflamed granulation tissue containing mixed lymphocytes, plasma cells, histiocytes, and neutrophils is a consistent finding within the CSDST (Figs. 8 and 9) (Martínez-Lage et al. 2011; De Vloo et al. 2013; Tisdall et al. 2015).
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 identified subcutaneous tissue. (Haematoxylin and eosin stain)

Fig. 9

Histological slides of the intradural portion of a dermal sinus tract (DST). (a) The intradural portion of a DST. (b) Magnified view showing granulation tissue. (Haematoxylin and eosin stain)

Fig. 10

Histological slide showing a cyst formed along a slender dermal sinus tract (the L1/L2 lesion in Fig. 4). (Haematoxylin and eosin stain)

Fig. 11

Histological slide showing 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)

Clinical Manifestations

The mean age of presentation is 3 years or below in most series, and 10 or below in all recent series. However, the age range is wide, with some patients first diagnosed in their 30s or even 50s (Table 1). Patients commonly present with skin stigmata, usually a cutaneous pit, frequently associated with haemangioma, pigmentation, skin tag, hypertrichosis, or subcutaneous lipomas (Fig. 3). The presence of the last two skin stigmata should arouse the suspicion for an associated split cord malformation or spinal cord lipoma. Neurological deficits involving the bowel and bladder and limbs are not rare and in many published series occur in over 40% of patients. Neurological deficits may develop catastrophically in infected cases and in patients harboring large intradural dermoid/epidermoid cysts (Table 1).

In clinical practice, a definitive history of discharge from a sinus ostium is uncommon, seen only in 25% of cases, and inflamed skin around an obviously infected ostium or a deep seated abscess is even rarer, occurring in less than 15%. Paradoxically, active meningitis or a history of recurrent meningitis is reported in up to 40% of cases in some series (Table 1).

Pure LDM

Morbid Anatomy

All LDMs share two constant features, namely, a cutaneous signature and an internal fibroneural stalk connecting the skin lesion to the spinal cord (Fig. 12). The cutaneous signature, a pearly crater of abnormal epithelium, commonly called a “cigarette-burn mark,” is caused by changes in the SE cells overlying the original site of nondisjunction (Fig. 2). The fibroneural stalk, beginning from the underside of the abnormal skin, ultimately merges with the spinal cord in all instances. In all cases, the attachment point is above the conus, indicative of this being a primary neurulation defect (Pang et al. 2013a). Only one case with a discontinuous stalk has been reported (Hiraoka et al. 2018). The fibroneural stalk, like the tract of a CSDST, has a V-shaped path on the sagittal plane when it is in the lumbosacral region, and becomes progressively horizontal or angles upwards with more cranial lesions.
Fig. 12

Classification of LDM into nonsaccular and saccular types, according to the two 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 fibroneural connections between the skin lesion and the spinal cord. (Reprinted from: Pang D, Zovickian J, Wong ST, Hou YJ, and Moes GS. Limited dorsal myeloschisis: a not-so-rare form of primary neurulation defect. Childs Nerv Syst (2013) 29:1459–1484; with permission from Springer Nature)

LDMs can be classified according to the appearance of the skin abnormality into either flat (nonsaccular) or saccular (Fig. 12). The flat LDM is recognizable either by a crater like patch of “nonskin” squamous epithelium or by a simple pit. Internally the fibroneural stalk runs through a small defect in the deep fascial layer and a bifid lamina towards the dura (Fig. 13a–e). On magnetic resonance imaging (MRI), the intradural stalk of a lumbar lesion is seen as a round structure separate from the filum and, more rostrally, separate from the conus (Fig. 13a), except where it joins the spinal cord to give it a trapezoid shape at the stalk-cord union, always at a level above the conus (Fig. 13b). In most lumbar lesions, the extradural stalk descends caudally from the skin lesion and then ascends towards the spinal cord after dural penetration, giving the tract a V-shape course on the sagittal MRI (Fig. 14). In thoracic lesions, the tract takes a straight slant upwards to meet the cord (Fig. 15). Some fibroneural stalks are stout and its tethering effect to the cord is very obvious (Fig.16). In others, the tension in the stalk is illustrated by a dorsally tented thecal sac at the point of dural penetration, and often the cord is also tented dorsally at the stalk-cord union (Fig. 17). Rarely, the cord appears to be archly pulled dorsally towards the skin crater to the extent it seems to have displaced the overlying bone and myofascial layers (Fig. 18). In all these examples, the apparent dynamism of the tethering is obvious.
Fig. 13

Lumbar nonsaccular (flat) LDM: (a) Sagittal MR showing subcutaneous fibroneural stalk going through laminar defect opposite L3/4, entering dura opposite L3, and joining spinal cord at L2. (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. (Reprinted from: Pang D, Zovickian J, Wong ST, Hou YJ, and Moes GS. Limited dorsal myeloschisis: a not-so-rare form of primary neurulation defect. Childs Nerv Syst (2013) 29:1459–1484; with permission from Springer Nature)

Fig. 14

Three cases of lumbar flat LDMs with V-shaped course of the LDM stalks: Upper: Crater is at L4/5, stalk enters thecal sac at S1, and joins spinal cord at upper margin of L2. Middle: Crater at L3/4, stalk enters dura probably at L5/S1, and joins spinal cord at L2. Right: Crater at L4/5, stalk enters dura around L5/S1, and joins spinal cord at L3. (Reprinted from: Pang D, Zovickian J, Wong ST, Hou YJ, and Moes GS. Limited dorsal myeloschisis: a not-so-rare form of primary neurulation defect. Childs Nerv Syst (2013) 29:1459–1484; with permission from Springer Nature)

Fig. 15

Upward coursing LDM stalk in a thoracic flat LDM. (a) Sagittal image shows skin crater at L1, extradural stalk at T12, dural entrance of the stalk above T12, and joining of stalk to spinal cord at T10. (b through e). show axial image of the LDM stalk at corresponding points shown in a. (Reprinted from: Pang D, Zovickian J, Wong ST, Hou YJ, and Moes GS. Limited dorsal myeloschisis: a not-so-rare form of primary neurulation defect. Childs Nerv Syst (2013) 29:1459–1484; with permission from Springer Nature)

Fig. 16

Thick upward slanting fibroneural stalk in a thoracolumbar (T11 / T12) LDM. (Reprinted from: Pang D, Zovickian J, Wong ST, Hou YJ, and Moes GS. Limited dorsal myeloschisis: a not-so-rare form of primary neurulation defect. Childs Nerv Syst (2013) 29:1459–1484; with permission from Springer Nature)

Fig. 17

Upper thoracic crater type 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: T1 sagittal MR; Middle: T2 sagittal MR; Right: axial MR. Note skin crater, subcutaneous tract and intradural course of the stalk are well shown on the T2 sagittal image. Also, fat is seen within the stalk. (Reprinted from: Pang D, Zovickian J, Wong ST, Hou YJ, and Moes GS. Limited dorsal myeloschisis: a not-so-rare form of primary neurulation defect. Childs Nerv Syst (2013) 29:1459–1484; with permission from Springer Nature)

Fig. 18

T5 LDM with nonsaccular skin crater showing extreme dural displacement and kinking of the thoracic cord presumably due to “pull” by a short, stout fibroneural stalk. Left: T1 sagittal MRI. Right: T2 sagittal MRI. This child had early neurological deficits. (Reprinted from: Pang D, Zovickian J, Wong ST, Hou YJ, and Moes GS. Limited dorsal myeloschisis: a not-so-rare form of primary neurulation defect. Childs Nerv Syst (2013) 29:1459–1484; with permission from Springer Nature)

Saccular LDMs probably have the same initial embryogenetic configuration as flat LDMs, but it is soon modified by the increasing hydrodynamic pressure of cerebrospinal fluid (CSF) which pushes the liquid up along the slender dural sleeve surrounding the fibroneural stalk to distend the skin above into a fluctuant sac. The internal content of the “sac” in saccular LDMs can be of three forms. First, if there is an associated hydromyelia within the part of the cord bearing the dorsal myeloschisis, CSF may distend the potential space in the center of the fibroneural stalk into a large myelocystocoele within the epithelium-covered sac (Fig. 19). This type of segmental myelocystocoele is found in many cervical cystic lesions (Fig. 20) (Suneson and Kalimo 1979; Steinbok and Cochrane 1991; Steinbok 1995; Rossi et al. 2006).
Fig. 19

Formation of saccular 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 CSF. The sac is covered by a full-thickness skin base and a thickened, distinctly different squamous epithelial dome. (Reprinted from: Pang D, Zovickian J, Wong ST, Hou YJ, and Moes GS. Limited dorsal myeloschisis: a not-so-rare form of primary neurulation defect. Childs Nerv Syst (2013) 29:1459–1484; with permission from Springer Nature)

Fig. 20

CT myelogram of a cervical saccular LDM with segmental myelocystocoele. The myelocystocoele sac does not contain contrast material, which remains in the subarachnoid space. (Reprinted from: Pang D, Zovickian J, Wong ST, Hou YJ, and Moes GS. Limited dorsal myeloschisis: a not-so-rare form of primary neurulation defect. Childs Nerv Syst (2013) 29:1459–1484; with permission from Springer Nature)

Second, in others saccular LDMs without hydromyelia, the fibroneural stalk remains compressed and narrow in its deeper course, but swells into basal neural nodules at the base of the fluid sac, while maintaining the original nondisjunctional connection with the SE (Figs. 21 and 22) (Schoenwolf 1979; Pang and Dias 1993, 2006; Steinbok 1995).
Fig. 21

Formation of a saccular LDM with basal neural nodule. In these cases, CSF dissects along the dural fistula ensheathing the fibroneural stalk and balloons out the less well-supported midline epithelial layer to give a CSF-filled sac, whose base is skin-covered. The neuroectoderm at the original site of nondisjunction swells to become the basal neural nodule. (Reprinted from: Pang D, Zovickian J, Wong ST, Hou YJ, and Moes GS. Limited dorsal myeloschisis: a not-so-rare form of primary neurulation defect. Childs Nerv Syst (2013) 29:1459–1484; with permission from Springer Nature)

Fig. 22

Cervical saccular LDM with basal neural nodule within the base of the CSF sac at the original nondisjunction site between cutaneous and neural ectoderms. (Reprinted from: Pang D, Zovickian J, Wong ST, Hou YJ, and Moes GS. Limited dorsal myeloschisis: a not-so-rare form of primary neurulation defect. Childs Nerv Syst (2013) 29:1459–1484; with permission from Springer Nature)

Third, in the least common form of saccular lesions, normal meninges develop around the neural tube and extend around the midline fibroneural stalk as a sleeve that projects to the surface. CSF squeezes into the dural fistula along the fibroneural stalk and ultimately distends the thinner, less well-supported squamous epithelial membrane into a fluid-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 crater, where the original nondisjunction occurred (Fig. 23).
Fig. 23

Thoracic saccular LDM with neural stalk that traverses the CSF sac and reaches the small skin crater at the top of the cystic dome, presumably the original site of disjunction failure. (Reprinted from: Pang D, Zovickian J, Wong ST, Hou YJ, and Moes GS. Limited dorsal myeloschisis: a not-so-rare form of primary neurulation defect. Childs Nerv Syst (2013) 29:1459–1484; with permission from Springer Nature)

Saccular LDMs therefore differ from the flat (crater or pit) type only in the fact that the apical epithelium at the dome has been subjected to modification by the distending forces of CSF. Depending on the fluid tension and the thickness of the apical epithelium and adjacent skin, the sac wall varies from the coarse, purplish, corrugated cap in the not-so-turgid tubular structures in many cervical saccular lesions, to the translucent membrane topping a tense lumbar sac, and finally to the giant, diaphanous bubble. The otherwise flat LDMs with the intermittently ballooning (to straining) central crater represent a transitional form between saccular and nonsaccular lesions (Fig. 24).
Fig. 24

Lumbar LDM showing a CSF-filled “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. (Reprinted from: Pang D, Zovickian J, Wong ST, Hou YJ, and Moes GS. Limited dorsal myeloschisis: a not-so-rare form of primary neurulation defect. Childs Nerv Syst (2013) 29:1459–1484; with permission from Springer Nature)

As with CSDST, documentation of the locations of LDMs has been far from ideal. The practical difficulty is due to the vast difference in the level of the skin lesion, the level where the fibroneural stalk penetrates dura and where it joins the dorsal spinal cord. In the largest LDM series published (Pang et al. 2013a), the vertebral level where the stalk joins the spinal cord was chosen as the level of the LDM because it is usually the easiest spot to recognize on MRI. The locations of the LDMs in that series are shown in Fig. 25, while the distribution of the types of LDMs is depicted in Fig. 26. Over two-thirds of LDMs in that series are located in the lower half of the spinal cord. In all variant forms of LDM, the spinal cord underneath is tethered to the myofascial tissue on the surface by the neural stalk (Steinbok and Cochrane 1991; Pang and Dias 1993; Steinbok 1995) and by the meningeal and other mesenchymal investments condensed around the stalk. Neurological deficits develop because of this tethering effect and vary according to the location of the LDM.
Fig. 25

Distribution of LDMs along the spinal axis. Designation of location is determined by the vertebral level where the fibroneural stalk attaches to the spinal cord. Note the two peaks at L2–L4 and C5–C7, and the absence of sacral lesion. (Reprinted from: Pang D, Zovickian J, Wong ST, Hou YJ, and Moes GS. Limited dorsal myeloschisis: a not-so-rare form of primary neurulation defect. Childs Nerv Syst (2013) 29:1459–1484; with permission from Springer Nature)

Fig. 26

Distribution of the four types of LDM classified according to external and internal features and assorted by regions of the spinal axis. The four types are flat (nonsaccular), saccular with basal neural nodule, saccular with neural stalk reaching the cyst dome, and saccular with segmental myelocystocoele. Note preponderance of the flat LDM in the lumbar and lower thoracic regions. Saccular types are seen in both cervical and lumbar segments. (Reprinted from: Pang D, Zovickian J, Wong ST, Hou YJ, and Moes GS. Limited dorsal myeloschisis: a not-so-rare form of primary neurulation defect. Childs Nerv Syst (2013) 29:1459–1484; with permission from Springer Nature)

Histologically, the central feature of all LDM stalks is neuroglial tissue, a hallmark of the stalk’s origin from the NE. It is either in large elongated swaths containing scattered neurons (Fig. 27a), or in nests embedded in dense fibrous tissue (Fig. 27b). Also found in every stalk is a profuse network of peripheral 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. 28). 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. 29). Pacinian corpuscles (Fig. 30) seen amongst some of these nerves suggest they are indeed sensory axons.
Fig. 27

Histopathology of LDM stalk. (a) Core of glial tissue with a large neuron, framed by fibrous tissue. (b) Nests of glial tissue (Gl) embedded in a dense fibrous matrix. (Reprinted from: Pang D, Zovickian J, Wong ST, Hou YJ, and Moes GS. Limited dorsal myeloschisis: a not-so-rare form of primary neurulation defect. Childs Nerv Syst (2013) 29:1459–1484; with permission from Springer Nature)

Fig. 28

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. (Reprinted from: Pang D, Zovickian J, Wong ST, Hou YJ, and Moes GS. Limited dorsal myeloschisis: a not-so-rare form of primary neurulation defect. Childs Nerv Syst (2013) 29:1459–1484; with permission from Springer Nature)

Fig. 29

LDM stalk containing glial tissue (Gl) and a large dorsal root ganglion (DRG). (Reprinted from: Pang D, Zovickian J, Wong ST, Hou YJ, and Moes GS. Limited dorsal myeloschisis: a not-so-rare form of primary neurulation defect. Childs Nerv Syst (2013) 29:1459–1484; with permission from Springer Nature)

Fig. 30

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. (Reprinted from: Pang D, Zovickian J, Wong ST, Hou YJ, and Moes GS. Limited dorsal myeloschisis: a not-so-rare form of primary neurulation defect. Childs Nerv Syst (2013) 29:1459–1484; with permission from Springer Nature)

Evidence of mesenchymal condensation around the lengthening neural stalk is shown by the almost universal inclusion of numerous fibrous bands, skeletal muscle, fat (Fig. 31), and prominent vascular channels sometimes in the form of a vascular glomus (Fig. 32). Glioependymal tissue lines the sac cavities of the cases of segmental myelocystocoeles (Fig. 33). The cutaneous “cigarette-burn mark” has the histological appearance of a dermal layer with engorged vascularity, abundant nerve fibers, and an abnormal collagen fiber matrix. The unevenness of its surface is due to the ruggedness of the epidermis and dermis (Fig. 34) (Morioka et al. 2018a, b).
Fig. 31

LDM stalk containing skeletal muscle (M), fat (F), and fibrous band (FB). (Reprinted from: Pang D, Zovickian J, Wong ST, Hou YJ, and Moes GS. Limited dorsal myeloschisis: a not-so-rare form of primary neurulation defect. Childs Nerv Syst (2013) 29:1459–1484; with permission from Springer Nature)

Fig. 32

LDM stalk containing prominent blood vessels (V) within a core of glial tissue (Gl), and fibrous bands (F), in the form of a vascular glomus. (Reprinted from: Pang D, Zovickian J, Wong ST, Hou YJ, and Moes GS. Limited dorsal myeloschisis: a not-so-rare form of primary neurulation defect. Childs Nerv Syst (2013) 29:1459–1484; with permission from Springer Nature)

Fig. 33

Glioependymal lining of a segmental myelocystocoele in a lumbar saccular LDM. Epen ependyma, Gl glial tissue. (Reprinted from: Pang D, Zovickian J, Wong ST, Hou YJ, and Moes GS. Limited dorsal myeloschisis: a not-so-rare form of primary neurulation defect. Childs Nerv Syst (2013) 29:1459–1484; with permission from Springer Nature)

Fig. 34

Histological slide of a skin “cigarette burn mark” showing increase vascularity, plenty of nerve fibers (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. 35a. (Haematoxylin and eosin stain)

The question is sometimes asked what constitute the minimum criteria for a diagnosis of LDM. It has been shown that there are patients with clinical and radiological features of LDM (Figs. 35 and 36) and most of its histological features including periphery nerve fibers, but no glial tissue within the stalk (Fig. 37) (Morioka et al. 2018a, b; Lee et al. 2017b). In many of these patients, melanocytes are also a prominent feature. Since periphery nerves and melanocytes are neural crest derivatives, and neural crest cells are located in the primary neural tube over the dorsal midline, a nondisjunctional stalk might drag with it neural crest progenitor cells without neuroglial progenitor cells (Schoenwolf 1979; Schoenwolf and Smith 1990; Colas and Schoenwolf 2001; Theveneau and Mayor 2012). Thus, the diagnosis of LDM can probably be applied in these patients with periphery nerve fibers but no glial tissue in the stalk.
Fig. 35

A case of “clinical and radiological” LDM. (a) Cigarette burn mark. (b) Mid-sagittal T2 weighted MRI image showing the intradural portion of the LDM stalk (yellow arrow). Blue arrow = 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

Fig. 36

Intraoperative photographs showing excision of a LDM with a L2 L3 laminoplasties. Preoperative MRI images and the skin lesion are shown in Fig. 35. 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

Fig. 37

Histological slide of the intradural portion of a LDM stalk showing the presence of nerve fibers and blood vessels. Intraoperative photograph is shown in Fig. 36. (Haematoxylin and eosin stain)

Clinical Manifestations

Most patients with LDMs also present at a young age. In Pang et al.’s (2013a) LDM series with a total of 63 patients, the mean age at presentation of 56 children was 5.9 years; and that of 7 adults was 28.2 years.

The skin abnormalities found in patients with LDM can be grouped according to their gross appearance into four distinct patterns, two flat, and two saccular, reflecting the two types of LDMs. The essential feature in all of them is a confined midline area of abnormal epithelium. The two flat lesions are: (1) Crater: The most common skin lesion seen in flat LDMs is a sunken crater on the flat skin surface made of pinkish squamous epithelium (Fig. 38a, b), often rimmed by elevated skin margin (Fig. 38c) and sometimes surrounded by a capillary haemangioma with irregular corrugated borders (Fig. 38d) or hyperpigmented skin (Fig. 38e). There are occasionally long hair emanating from the crater (Fig. 6f), and some craters are edged by hooded overhanging skin (Fig. 38g). In several examples, the crater is adjacent to an area of wrinkly, over-stretched skin that periodically distends with CSF on dependent posturing or straining (Fig. 39a). Very rarely, the center of the crater is adorned with a CSF-filled blister (Fig.39b). These latter examples are transitional forms between saccular and nonsaccular lesions. (2) Pit: The most subtle cutaneous signature in a flat LDM is a small midline pit with no other unusual features (Fig. 40), easily missed on cursory examination. Sometimes the pit situates within a capillary haemangioma. Pit lesions are usually found in low thoracic and lumbar cases. The skin pit seen in some LDM might be confused with that seen in a CSDST.
Fig. 38

Nonsaccular or flat type skin lesions in LDM: (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 nonmelanotic, 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). (Reprinted from: Pang D, Zovickian J, Wong ST, Hou YJ, and Moes GS. Limited dorsal myeloschisis: a not-so-rare form of primary neurulation defect. Childs Nerv Syst (2013) 29:1459–1484; with permission from Springer Nature)

Fig. 39

Nonsaccular LDMs with transitional skin lesions: (a) Lumbar LDM with a flat epithelial crater and an adjacent area made of stretchable, nonskin 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. (Reprinted from: Pang D, Zovickian J, Wong ST, Hou YJ, and Moes GS. Limited dorsal myeloschisis: a not-so-rare form of primary neurulation defect. Childs Nerv Syst (2013) 29:1459–1484; with permission from Springer Nature)

Fig. 40

Subtle pit (within circle) in a flat lumbar LDM with no surrounding exuberance. (Reprinted from: Pang D, Zovickian J, Wong ST, Hou YJ, and Moes GS. Limited dorsal myeloschisis: a not-so-rare form of primary neurulation defect. Childs Nerv Syst (2013) 29:1459–1484; with permission from Springer Nature)

The two saccular skin lesions are: (1) Skin-based Sac: This type consists of a skin-based, CSF-filled sac with a dome of tissue that is distinctly not full-thickness skin. Three subtypes can be distinguished according to the character of the dome cover. One subtype has a wide top of purplish, raw-looking, thick stratified squamous epithelium (Fig. 41a). Another subtype has a much smaller, discrete, pale, puckered crater of squamous epithelium on the dome (Fig. 41b). A third subtype has a small, almost imperceptible patch of ultra-thin epithelium on the apex of the relatively delicate skin- based dome (Fig. 41c). (2) Membranous Sac: This is the rarest skin lesion. An example is a tubular, CSF-filled sac made of a diaphanous membrane resembling thickened arachnoid, protruding through a 4 mm skin-lined dorsal defect (Fig. 42). The base of this sac has a shallow collar of skin similar to the commoner form of saccular skin lesions. The types and locations of the cutaneous lesions are summarized in Table 2.
Fig. 41

Saccular skin lesions in 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 “nonskin” epithelial top. (Reprinted from: Pang D, Zovickian J, Wong ST, Hou YJ, and Moes GS. Limited dorsal myeloschisis: a not-so-rare form of primary neurulation defect. Childs Nerv Syst (2013) 29:1459–1484; with permission from Springer Nature)

Fig. 42

Lumbar 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 surgery to show basal neural nodules (BN), subcutaneous tract, and intradural stalk (S) attached to the spinal cord. (Reprinted from: Pang D, Zovickian J, Wong ST, Hou YJ, and Moes GS. Limited dorsal myeloschisis: a not-so-rare form of primary neurulation defect. Childs Nerv Syst (2013) 29:1459–1484; with permission from Springer Nature)

Table 2

Skin Lesions in LDM in Different LDM Locations (n = 63) (From Pang et al. 2013a)

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

Reprinted from: Pang D, Zovickian J, Wong ST, Hou YJ, and Moes GS. Limited dorsal myeloschisis: a not-so-rare form of primary neurulation defect. Childs Nerv Syst (2013) 29:1459–1484; with permission from Springer Nature

It is noteworthy that other cutaneous markers of dysraphism such as hypertrichosis, capillary haemangioma, or misaligned gluteal crease are never seen alone in LDM without the quintessential epithelial crater or pit. The pearly midline crater in a nonsaccular LDM thus remains the single most important diagnostic clue for LDM, especially before the development of neurological symptoms.

LDMs cause neurological deficits solely by their tethering effect. By and large, LDM patients tended to have milder disability than patients with other forms of dysraphic malformations such as spinal cord lipomas and split cord malformations. In Pang et al.’s series, half of the LDM patients are neurologically normal at presentation, which underscores the importance of the cutaneous signature as an initial diagnostic clue. Only 10% of patients had significant weakness and neuropathic bladder and the rest of the patients had mild or tolerable neurological or urological symptoms, with relatively little hindrance to their lifestyle. The types of deficits corresponding locations of the LDMs are summarized in Table 3. The proximity of tension on 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 thoracic lesions. Lumbar LDMs close to the conus are perhaps more treacherous because they more often implicate the bladder yet are more likely to be occult.
Table 3

Types of neurological deficits in different LDM Locations (n = 63)

Neurological status

Number of patients assorted by LDM location

Cervical (11)

Thoracic upper (9)

Thoracic lower (7)

Thoracolumbar (8)

Lumbar (28)

Normal

4 (36%)

2 (22%)

4 (57%)

4 (50%)

14 (50%)

UE weakness/sensory loss

7 (64%)

2 (22%)

   

LE weakness

1 (9%)

2 (22%)

3 (43%)

3 (38%)

14 (50%)

LE sensory loss

 

1 (11%)

2 (31%)

1 (13%)

8 (29%)

Spastic legs

4 (36%)

4 (44%)

2 (31%)

  

Back pain

  

1 (25%)

 

3 (13.6%)

Foot deformity

    

2 (9.1%)

Scoliosis

  

2 (31%)

1 (16.6%)

1 (4.5%)

Neurogenic bladder

  

1 (25%)

1 (16.6%)

4 (18%)

Abnormal URD

  

1 (25%)

1 (16.6%)

2 (9.1%)

Reprinted from: Pang D, Zovickian J, Wong ST, Hou YJ, and Moes GS. Limited dorsal myeloschisis: a not-so-rare form of primary neurulation defect. Childs Nerv Syst (2013) 29:1459–1484; with permission from Springer Nature

LE Lower extremity, UE Upper extremity; URD Urodynamics

As with other tethering lesions, the probability of neurological injury increases with longitudinal growth of the spine and with time. Pang et al. demonstrated that there was a tendency for older patients with LDMs to present with more severe neurological and urological disability; and that infants and young children were more likely to be neurologically intact, while adult patients were usually significantly disabled at diagnosis (Figs. 43 and 44). Longitudinal follow-up of four adolescents from the series who had delay of surgery of 1–9 years all showed neurological deterioration.
Fig. 43

Linear regression analysis between neurological grade and patient age shows a logistical tendency for older patients with LDM to present with higher grades of neurological deficits. (Correlative coefficient R2 = 0.642). (Reprinted from: Pang D, Zovickian J, Wong ST, Hou YJ, and Moes GS. Limited dorsal myeloschisis: a not-so-rare form of primary neurulation defect. Childs Nerv Syst (2013) 29:1459–1484; with permission from Springer Nature)

Fig. 44

Clustered bar graphs showing neurological grade assorted by patients’ age-groups (birth to 6 months; 6–12 months; 1–5 years; 6–10 years; 11–18 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. (Reprinted from: Pang D, Zovickian J, Wong ST, Hou YJ, and Moes GS. Limited dorsal myeloschisis: a not-so-rare form of primary neurulation defect. Childs Nerv Syst (2013) 29:1459–1484; with permission from Springer Nature)

Mixed CSDST and LDM

Lesions clearly composed of the essential features of both CSDSTs and LDMs were first reported in 2013 (Pang et al. 2013a). They are rare compared to CSDSTs and LDMs. Among a series of 75 cases of LDM, there were five cases of this mixed type (Eibach et al. 2017). In another series of 51 cases that consisted of 11 CSDSTs and 40 LDMs, another five cases were observed (Lee et al. 2018).

Macroscopically, a mixed lesion of CSDST and LDM can mimic either of the pure forms. Even cystic type has been observed (Lee et al. 2018). Thus, their recognition relies on histology. Two histological types are seen. In the “regular” type, the neuroglial, and dermoid elements are in their respective embryological orthodox positions, i.e., an outer tract of CSDST and an inner tract of LDM elements (Lee et al. 2018). However, an “irregular” type has also been observed in which the dermal elements form squamous epithelial islands within the neuroglial tissue of the LDM tract (Fig. 45) (Tisdall et al. 2015; Eibach et al. 2017).
Fig. 45

An LDM stalk containing contiguous glial tissue and dermoid cyst. Insets show both tissues in high power. This reflects the original undisjointed connection between cutaneous and neural ectoderms. (Reprinted from: Pang D, Zovickian J, Wong ST, Hou YJ, and Moes GS. Limited dorsal myeloschisis: a not-so-rare form of primary neurulation defect. Childs Nerv Syst (2013) 29:1459–1484; with permission from Springer Nature)

The most important practical point with the discovery of this mixed entity 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 should be removed from skin to spinal cord. A postoperative follow-up MRI should be done to rule out a recurrent dermoid cyst.

LDSND with Spinal Cord Lipomas, Split Cord Malformations, and Other Dysraphic Malformations

LDSNDs have been reported to coexist with other dysraphic or paradysraphic malformations such as spinal cord lipomas, split cord malformations, myelomeningoceles, and neurenteric cysts (Table 4) (Fig. 46). In such cases, the complex anatomy of the other anomalies usually determines the dominant features of the composite malformation, for a pure LDSND lesion is structurally subtler unless it is a CSDST with a large intradural dermoid/epidermoid cyst.
Table 4

Associated anomalies in LDM (n = 63) (From Pang et al. 2013a)

Anomalies

LDM location

Cervical (11)

Thoracic upper (9)

Thoracic lower (7)

Thoracolumbar (8)

Lumbar (28)

SCM

4

1

  

1

Terminal lipoma

 

1

  

1

Dorsal lipoma

 

1

 

2

3

Thickened filum

2

1

 

3

21

Neurenteric cyst

    

1

Syringomyelia

 

1

 

1

 

Chiari II

3

2

   

Hydrocephalus

6

    

Dermal sinus

  

1

1

1

Velum interpositum cyst

 

1

   

Vertebral/rib fusion

 

2

1

  

Reprinted from: Pang D, Zovickian J, Wong ST, Hou YJ, and Moes GS. Limited dorsal myeloschisis: a not-so-rare form of primary neurulation defect. Childs Nerv Syst (2013) 29:1459–1484; with permission from Springer Nature

Fig. 46

MRI images showing a LDM associated with a transitional spinal cord lipoma in a 11-month-old. The axial cuts are numbered according to the cut-lines on the T2-weighted mid-sagittal MRI image. Arrow head = the subcutaneous portion of the LDM stalk. The stalk was confirmed intraoperatively to pass through bifid S1 and S2 laminae

The clinical manifestations of these composite lesions also follow the usual course of the associated anomalies, especially when there are only LDM elements without dermoid cyst. However, if present, the dermal elements can have major clinical impact due to their inherent risks of infection, inflammation, proliferation producing mass effect, and recurrence if not completely removed. One should therefore always be vigilant for hidden dermoid elements when dealing with spinal dysraphic lesions.

Evaluation

Clinical Assessment and Laboratory Studies

As with any medical conditions, a thorough clinical history and physical examination to elicit all the relevant features are paramount. Apart from the obvious symptoms and signs related to the location and types of LDSNDs, past or active infection, changes in neurourological functions, and clues to the existence of associated anomalies should also be documented. Thus, physical examination of the whole cranio-spinal axis is needed. Urological evaluation including urodynamic studies, ultrasonography of the urinary system, voiding cystourethrogram, and urinalysis should also be performed with a low threshold of suspicion for abnormality.

Neuroimaging

When a patient presents with a midline skin lesion, MRI is the diagnostic method of choice to display the anatomical details of the malformation especially regarding composite lesions. Urgent MRI is indicated if there are acute neurological deficits, or symptoms and signs of central nervous system infection. Time should not be wasted with ultrasonography, a seldom-definitive modality. Nowadays, injecting a sinus should never be performed. Computed tomographic (CT) myelography is only indicted if certain bony structures need to be minutely visualized in context, such as the midline bone spikes of a type I split cord malformation. Plain radiographs of the spine, however, retain its role in demonstrating any obvious bony deformity, and in planning incision for surgery.

MRI of the whole spine with T1- and T2-weighted images and occasionally T1-weighted sequences with gadolinium in both sagittal and axial planes should be done. Diffusion weighted imaging sequence for cases with larger cysts should be considered. MRI features suggestive of LDSND are: (1) a tract linking the skin and the spinal cord even it does not appear continuous (Figs. 4, 5, 6, 13,); (2) posteriorly tacked-up spinal cord (Figs. 13, 14, 16, 17, and 18); and (3) a cystic lesion over the dorsal midline (Figs. 7, 15, 20, 22, 23, 24). When LDSND 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. 46): any cyst along its course or in the vicinity is particularly noted (Figs.7, 15, 20, 22, 23, and 24), 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 LDSNDs in the same spine (Fig. 47).
Fig. 47

Double LDMs, both crater type, with accompanying dorsal lipomas. The lower LDM is at L2/3, and upper LDM is at T12. Both accompanying lipomas are just rostral to the LDM stalk. (Reprinted from: Pang D, Zovickian J, Wong ST, Hou YJ, and Moes GS. Limited dorsal myeloschisis: a not-so-rare form of primary neurulation defect. Childs Nerv Syst (2013) 29:1459–1484; with permission from Springer Nature)

Nevertheless, the reliability of MRI in delineating LSDNDs is far from absolute. For example, a small tract can be below its resolution (Fig. 5) (Tisdall et al. 2015; Lee et al. 2017a), and it cannot always differentiate a CSDST from a LDM, except when the CSDST becomes inflamed and exhibits abnormal enhancement of the tract, a constituent cyst, and adjacent meninges (Fig. 4) (De Vloo et al. 2013). All are essential information for surgical planning.

Management

All LDSNDs can produce functional impairment by tethering of the spinal cord, while CSDST or any of its mixed forms pose additional risks of inflammation, 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 with pure LDM, we also strongly recommend surgery to obviate the dreadful consequences of late and unrecognized tethering. Observation by serial MRI is probably only indicated in cases with equivocal MRI findings or perhaps in asymptomatic adults.

For CSDST patients with active infection and neurological deficits, urgent surgery covered with appropriate antibiotics should be done. However, if skin infection is localized or meningitis is not accompanied by neurological deficits, surgery should be deferred until the infection has been treated with antibiotics and local therapy.

Surgery

The aims of surgery in all LDSNDs are to untether 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 needed. 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 suddenly becomes trapezoid instead of the normal ovoid. In uncertain cases, the skin should be widely draped to accommodate 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 LDSND, so that appropriate provision must be made for more caudal exposure.

Surgical Technique for CSDST

The patient is laid prone, the skin ostium of the sinus tract identified, and the laminae of the planned laminectomy confirmed with radiograph (Fig. 48). Standard midline skin incision with a small elliptical island around the sinus opening 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 laminectomy is then carried out carefully around the tract. Dissection of the tract should be done under magnification to minimize the possibility of leaving behind residuum (De Vloo et al. 2013). The dura should always be opened unless the surgeon is absolutely certain that the tract ends outside the dura. When the tract goes intradurally, 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 laminectomy technique should be considered in which some laminae between the tract’s dural entry point and its spinal cord attachment point are strategically kept intact. The CSDST tract can be carefully delivered in between the laminectomy gaps (Fig. 49). Afterwards, primary closure of the dura is usually possible.
Fig. 48

Intraoperative 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). (bg) Caudal. (hk) Rostral wound (a) Skin preparation. Yellow lines = skin incisions. Numbers in black on skin = levels of lumbar spinous processes. (b) L4 L5 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 filum. (g) The caudal portion of the DST has been completely removed via the L4 L5 laminectomy. (h, i) Operative exposure via a T12 L1 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 DSTrostral 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 submillimeter thickness of the DST testifies 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

Fig. 49

Mid-sagittal MRI image showing the postoperative appearance of a skip laminectomy technique in which T12 laminoplasty, L1 laminectomy, and L4 L5 laminectomy were done. White triangle = laminoplasty level. White star = intact laminae level

The sinus tract may expand along its course or terminate into a dermoid or epidermoid cyst. Extradurally located cysts are readily excised. For large intradural cysts, refined microsurgical techniques are required for their complete removal since the cyst wall is notoriously adherent to nerve roots and pia (Figs. 50 and 51). Microbial cultures from adjacent areas should be obtained, and postoperative antibiotics should be given until negative growth is documented.
Fig. 50

Intraoperative 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

Fig. 51

6-year postoperative MRI images (of the patient shown in Figs. 7 and 50) showing no recurrence of the dermoid cyst, and postlaminoplasty changes. (a) T2-weighted MRI. (b) T1-weighted MRI with gadolinium injection

Surgical Technique for Flat LDM

The operative strategy for flat LDMs is similar to that for CSDST. After a standard midline skin incision, the skin crater or pit is excised and the stalk at the base of the crater is carefully dissected out and followed through the discrete myofascial defect and the bifid laminae (Fig. 52a). To afford good visualization of the stalk-spinal cord attachment, at least one set of laminae both rostral and caudal to the stalk-spinal cord union site has to be removed (Fig. 52b). Again, if the stalk spans multiple levels, skip laminectomy may be used.
Fig. 52

Surgical resection of a lumbar crater-type flat (nonsaccular) LDM. (a) Ellipse of resected skin crater and subcutaneous tract going through defect in lumbodorsal fascia. (b) Extradural stalk and dural fistula. (c) Intradural exposure showing stalk-cord union. (d) Resection of stalk flush 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 arrow head), and an exuberant cuff of tissue on the cord. (Reprinted from: Pang D, Zovickian J, Wong ST, Hou YJ, and Moes GS. Limited dorsal myeloschisis: a not-so-rare form of primary neurulation defect. Childs Nerv Syst (2013) 29:1459–1484; with permission from Springer Nature)

The dura is incised in the midline centered upon the entry point of the fibroneural stalk and extended according to the track of the stalk 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. 52c); it is simply cut flush with the cord surface (Fig. 52d, e). Any peripheral nerve twigs, blood vessels, and fibrous bands encircling the neural stalk are similarly cut. Once the intradural stalk had been disconnected from the cord, the external stalk with its skin appendage is resected en bloc (Fig. 52f).

The LDM stalk may be exceedingly slender and attaches to the cord in a minute midline scar (Fig. 53), 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. 54). The stalk may also contain a glomus of vascular channels (Fig. 55), or its proximal end expands into tentacles of blood vessels that crawl on to the cord (Fig. 56a, b). Rarely, the stalk attachment is stout and deceptively complex, and the dorsal roots surround it like a cuff (Fig. 57a, b). These attachments are cut flush as above but sparing the surrounding nerve root to reveal a large base of raw spinal cord (Fig. 57b). Rarely, it is necessary to approximate the pial edges of the large raw bed of a pure LDM to eliminate a potentially adherent surface susceptible to re-tethering (Fig. 58). The dura is closed primarily.
Fig. 53

Exceedingly slender 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. (Reprinted from: Pang D, Zovickian J, Wong ST, Hou YJ, and Moes GS. Limited dorsal myeloschisis: a not-so-rare form of primary neurulation defect. Childs Nerv Syst (2013) 29:1459–1484; with permission from Springer Nature)

Fig. 54

Moderate-sized LDM stalk: (a) Stalk has a flared-out cord attachment (b) Stalk resection leaves a fish-mouth shaped scar. (Reprinted from: Pang D, Zovickian J, Wong ST, Hou YJ, and Moes GS. Limited dorsal myeloschisis: a not-so-rare form of primary neurulation defect. Childs Nerv Syst (2013) 29:1459–1484; with permission from Springer Nature)

Fig. 55

Long LDM stalk with vascular glomus (at tip of forceps). (Reprinted from: Pang D, Zovickian J, Wong ST, Hou YJ, and Moes GS. Limited dorsal myeloschisis: a not-so-rare form of primary neurulation defect. Childs Nerv Syst (2013) 29:1459–1484; with permission from Springer Nature)

Fig. 56

Moderately thick 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

Fig. 57

Thick, complex-looking fibroneural stalk in a lumbar nonsaccular LDM: (a) Lesion contains dysplastic spinal cord tissue, large blood vessels, ample skein of nonfunctioning nerves, and thickened folded membranes. Spinal cord is lifted dorsally by the tethering effect. (b) Bizarre arrangement of dorsal roots (DR), and dorsal root entry zone (DREZ) surround a large flat myeloschistic scar after stalk resection

Fig. 58

Crater type lumbar 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

Surgical Technique for Saccular LDMs

The technique of dealing with the internal structures of LDMs is essentially the same whether the LDM is saccular or nonsaccular. The minor differences between the two types lay in handling the initial soft tissue dissection. For the saccular LDMs, a large skin ellipse is made at the sessile base of the sac to expose the dural funnel where the narrow dural fistula fans out to form the sac at the skin level (Fig. 59a). The dural fistula is then followed to the bifid laminae as with the nonsaccular type (Fig. 59b).
Fig. 59

Large cervical saccular LDM. (a) Exposure of the dorsal fistula 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 fistula opening (into the cyst) are seen through the cavity. (d) Dural fistula opened into the main thecal sac, showing the thin fibroneural stalk inserting on to the dorsal spinal cord. (e) Stalk being resected. All insets show exact level of the exposure

For the basal nodule type of saccular LDM, the sac is entered at the base to locate the basal neural nodule (Fig. 59c) and the underlying fibroneural stalk within the dural fistula, where it is traced to its attachment to the cord and removed (Fig. 59d, e). Saccular LDMs with very thick stalks that traverse the cyst to reach the dome are exposed from the spinal cord side up towards the top (Fig. 60). The base of the stalk is then disconnected from the cord surface. In large saccular lesions with slender stalks that may be hard to find, the sac is opened at the dome and the neural stalk is located at the base of the abnormal skin crater, then traced to the spinal cord surface where it is transected (Fig. 61). In lower thoracic and lumbar saccular myelocystocoeles, the stalk may be longer than expected and its cut end can often be traced directly into the hydromyelic center of the cord (Fig. 62).
Fig. 60

Thoracic Saccular LDM with the fibroneural stalk (displayed by instrument) traversing the sac cavity and reaching the dome of the sac

Fig. 61

Saccular LDM with the stalk-to-dome subtype of fibroneural stalk attachment. (a) T2 MR shows slight tenting of the cord towards the sac on the sagittal image, and the fibroneural 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 inserting on the dorsal cord surface (upper). After resecting these strands (lower), the cord surface shows abnormal clusters of wiggly blood vessels and scar tissue

Fig. 62

Lumbar saccular LDM with segmental myelocystocoele. (a) A long intradural stalk (S) picked up by microforceps. (b) Stalk traced to the hydromyelic portion of the cord after partial stalk resection. C Conus

Surgical Techniques for LDSNDs Associated with Other Anomalies.

The surgical strategy in these situations is a combination of the above technique with the specific techniques suitable for the associated anomalies (Pang et al. 2013a, b). The technique for the associated anomaly usually predominates (Figs. 63, 64). The most salient point to note is the essential total extirpation of any dermoid elements in a complex lesion.
Fig. 63

Intra-operative photographs showing the excision of a LDM – lipoma complex (MRI images are shown in Fig. 46). (a) The skin lesion, a cigar burn crater with surrounding skin discoloration. (b) Markings for the skin incision. (c) Surgical exposure after 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 final trimming. (h) Appearance of the spinal cord after neurulation. The nerve roots at the end of the spinal cord were stimulation positive. Blue arrow = Extradural portion of the LDM. The patient has no neurological deficits before and after the untethering surgery

Fig. 64

Postoperative 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 fluid

Outcomes and Conclusion

The clinical outcome of LDSNDs is dictated by the clinical condition at presentation. In LDSNDs without large intradural dermoid/epidermoid cysts, the surgery is usually uncomplicated; and recurrence of dermal elements and re-tethering should be extremely rare. With proper surgical techniques, most LDSND patients without neurological deficits remain neurologically normal after surgery (Wang et al. 1993; Ackerman and Menezes 2003; Pang et al. 2013a). Over two thirds of patients with preoperative neurological deficits improve after surgery; about one third will not improve though remain stable (Wang et al. 1993, Ackerman and Menezes 2003; Pang et al. 2013a). In CSDST patients with large intradural dermoid/epidermoid cysts or active infections, the results are less salubrious (Ackerman and Menezes 2003; van Aalst et al. 2006; Girishan and Rajshekhar 2016) (Tables 1 and 5). These statistics thus highlight the importance of early detection and prompt surgical intervention in LDSNDs.
Table 5

Preoperative, 3-month postoperative, and 1 year postoperative neurological grades in LDMa patients grouped against LDM location

LDM location

Preoperative grade

Postoperative grade

3 Months

1 Year

0

1

2

3

0

1

2

3

0

1

2

3

Cervical (11)

4

4

3

0

4

5

2

0

7

4

0

0

Thoracic upper (9)

2

6

1

0

3

6

0

0

6

3

0

0

Thoracic lower (7)

4

2

0

1

4

2

1

0

4

2

1

0

Thoracolumbar (8)

4

3

0

1

4

3

1

0

5

3

0

0

Lumbar (28)

15

8

3

2

17

6

4

1

20

7

0

1

Total number of patients 63

29

23

7

4

32

22

8

1

42

19

1

1

Reprinted from: Pang D, Zovickian J, Wong ST, Hou YJ, and Moes GS. Limited dorsal myeloschisis: a not-so-rare form of primary neurulation defect. Childs Nerv Syst (2013) 29:1459–1484; with permission from Springer Nature

aNeurological grading system in LDM. Grade 0: No deficits 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

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Copyright information

© Springer Nature Switzerland AG 2019

Authors and Affiliations

  1. 1.Department of NeurosurgeryTuen Mun HospitalHong KongChina
  2. 2.Department of Clinical PathologyTuen Mun HospitalHong KongChina
  3. 3.University of CaliforniaDavisUSA
  4. 4.Great Ormond Street Hospital For Children, NHS TrustLondonUK

Section editors and affiliations

  • Dachling Pang
    • 1
  • Kyu-Chang Wang
    • 2
    • 3
  • Dominic N. P. Thompson
    • 4
  1. 1.LondonUK
  2. 2.Division of Pediatric NeurosurgerySeoul National University Children’s HospitalSeoulSouth Korea
  3. 3.Division of Pediatric NeurosurgerySeoul National University Children’s Hospital & Seoul National University College of MedicineSeoulSouth Korea
  4. 4.Department of NeurosurgeryGreat Ormond Street HospitalLondonUK

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