J Korean Neurosurg Soc.  2022 Jan;65(1):138-144. 10.3340/jkns.2020.0360.

Type 1.5 Split Cord Malformation : A New Theory of Pathogenesis

• Sun M
• Tao B
• Luo T
• Gao G
• Shang A

• KMID: 2523922
• DOI: http://doi.org/10.3340/jkns.2020.0360

Abstract

To report two cases of type 1.5 split cord malformation (SCM), a subtype of SCM with combined characteristics of types I and II and to review the relevant literature and propose a new possible pathogenetic theory for type 1.5 SCM. A 52-year-old woman had hemicords within a single dural sac with a dorsal bony septum at the L5 level. A 9-year-old boy had hemicords within a single dural sac with a ventral bony septum and fibrous extension at the L3 level. Both patients underwent microsurgical treatments for removing the bony septum, detethering the spinal cord, and sectioning the filum terminale. The surgical procedure revealed an extradural partial bony septum and hemicords within an intact single dural sac in each patient. Both patients were discharged from the hospital without de novo nerve dysfunction. Published cases have validated that types I and II SCM can overlap. We recommend recent type 1.5 SCM as a normative terminology for this overlapping SCM and report two rare cases of this SCM. We propose an associated pathogenesis consisting of uneven distribution and regression to explain type 1.5 SCM. Furthermore, we postulate that the amount of condensing meninx primitiva might determine whether the left bony septum has fibrous extensions to the opposite dura in type 1.5 SCM.

Keyword

Split cord malformation; Pathogenesis; Embryogenesis; Meninx; Regression

Figure

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  Fig. 1. The lumbosacral dermal sinus (about 4×4 cm) with central hyperpigmentation (A). Magnetic resonance imaging suggesting a dorsal bulging lesion (arrowhead) at the L5 level and a low conus at the S1 level (B : axial T1-weighted sequences; C : sagittal T1-weighted sequences; D : sagittal T2-weighted sequences).

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  Fig. 2. Computed tomography suggesting a dorsal bony septum (asterisk) at the L5 level (A : sagittal view; B : coronal view; C : axial view). A partially resected dorsal bony septum (asterisk) found intraoperatively. Its base was sectioned during the primary laminectomy (D).

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  Fig. 3. Magnetic resonance imaging suggesting a ventral spinous lesion (arrow) at the L3 level and a low conus at the L5 level (A : sagittal T1-weighted sequences; B : sagittal T2-weighted sequences; C: axial T2-weighted sequences). Split spinal cord (D).

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  Fig. 4. Computed tomography (CT) demonstrating a ventral bony septum (dotted arrow) at the L3 level (A : sagittal view; B : axial soft-tissue window; C : axial bone window). Three-dimensional CT reconstruction indicating lumbosacral spina bifida (D).

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  Fig. 5. A : An intact single dural sac. B : A fibrous extension to the dorsal dura (pound). C : A ventral bony septum (cross). D : Complete resection of the bony septum.

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  Fig. 6. A relatively lower proportion of meninx primitiva near the neural arch regressing into a fibrous extension from the ventral bony septum in case 2 (A). Few meninx primitiva cells existing around the vertebral body, resulting in a regressed dorsal bony septum without any ventral fibrous extension in case 1 (B).

Reference

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