J Korean Neurosurg Soc.  2020 May;63(3):314-320. 10.3340/jkns.2020.0052.

Secondary Neurulation Defects-1 : Retained Medullary Cord

Affiliations
  • 1Division of Pediatric Neurosurgery, Seoul National University Children's Hospital, Seoul, Korea
  • 2Department of Anatomy, Seoul National University College of Medicine, Seoul, Korea

Abstract

Retained medullary cord (RMC) is a relatively recent term. Pang et al. newly defined the RMC as a late arrest of secondary neurulation leaving a non-functional vestigial portion at the tip of the conus medullaris. RMC, which belongs to the category of closed spinal dysraphism, is a cord-like structure that is elongated from the conus toward the cul-de-sac. Because intraoperative electrophysiological confirmation of a non-functional conus is essential for the diagnosis of RMC, only a tentative or an assumptive diagnosis is possible before surgery or in cases of limited surgical exposure. We suggest the term ‘possible RMC’ for these cases. An RMC may cause tethered cord syndrome and thus requires surgery. This article reviews the literature to elucidate the pathoembryogenesis, clinical significance and treatment of RMCs.

Keyword

Secondary neurulation; Conus medullaris; Intraoperative electrophysiological monitoring; Closed spinal dysraphism; Tethered cord syndrome

Figure

  • Fig. 1. Magnetic resonance imaging of a patient with ‘terminal syrinx with low-lying conus’. a : This demonstrates that the thick medullary cord extends down to the lower lumbar area, where it ends with a cyst that attaches to the cul-de-sac. B-D : They show T2 axial images at L3 (yellow line in a), L5 (orange line), and S1–2 (blue line), respectively.

  • Fig. 2. Schematic illustrations of three types of non-cystic RMCs. Fine vestigial nerve twigs emanate from the medullary cord. a : It shows a typical RMC. B : It reveals no terminal tapering but enlargement of the conus with gradual transition to a fat-containing mass at the end. The ‘cord portion’ has a non-functional part in the RMC, which is different from a simple caudal lipoma. C : It shows an hourglass-shaped RMC with an intervening filum-like structure between the conus and RMC. If the part distal to the filum-like structure is functional but not electrophysiologically connected to the ‘upper cord’, it is considered a junctional neural tube defect. RMC : retained medullary cord.

  • Fig. 3. MRI of a ‘possible retained medullary cord’ patient. a : The medullary cord partially contains fat tissue, resulting in high signal intensity in the T1-weighted MR image (arrow in C). In this case, only a small segment of the distal part was resected through a limited exposure of the lipoma. Exploration of the whole conus area, which may include the non-functional parts, was not performed. B and C : They show axial images at L4 (yellow line in a) and S1 (blue line), respectively. MRI : magnetic resonance imaging.

  • Fig. 4. MRI of an RMC patient. a : The signal intensity is indistinguishable between the spinal cord and the RMC. On operation, the non-functional part of the RMC was identified by electrophysiological monitoring and was resected. B : axial images at L4-5 (yellow line in a). MRI : magnetic resonance imaging, RMC : retained medullary cord.

  • Fig. 5. Magnetic resonance imaging and intraoperative photograph of a retained medullary cord patient. a : a cord-like structure extending to the sacral area. B : axial images at L5 (yellow line in a). C : The limited L5 unilateral partial hemilaminectomy shows a thick, pia-covered medullary cord passing through. D : after resection of the non-functional medullary cord. Pial reconstruction was performed at the most caudal part of the cord. Removal of the non-functional segment creates a gap and may reduce the chance of retethering compared with just cutting.


Cited by  2 articles

Disorders of Secondary Neurulation : Mainly Focused on Pathoembryogenesis
Jeyul Yang, Ji Yeoun Lee, Kyung Hyun Kim, Kyu-Chang Wang
J Korean Neurosurg Soc. 2021;64(3):386-405.    doi: 10.3340/jkns.2021.0023.

Perspectives : The Role of Clinicians in Understanding Secondary Neurulation
Kyu-Chang Wang
J Korean Neurosurg Soc. 2021;64(3):414-417.    doi: 10.3340/jkns.2021.0040.


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