Surgical treatment of a combined split cord malformation and spinal cord lipoma: illustrative case

Abstract

BACKGROUND

Split cord malformations (SCMs) are uncommon congenital anomalies that are usually detected in children, but can present in adulthood with signs and symptoms of spinal cord tethering. SCMs rarely occur in association with a lipoma and a defect in the posterior elements.

OBSERVATIONS

A 37-year-old man presented with 6 months of new-onset leg weakness, urinary urgency, and reduced sensation in his feet. He developed pain radiating from his low back into his legs, worsened by bending forward and walking. Prior to this presentation, he had not noticed any symptoms. MRI revealed a congenital fusion from L2 to L4 with a type I SCM and a lipoma extending through a dorsal bony defect and terminating at the duplicated spinal cord. A posterior L2–4 lumbar laminectomy was performed to excise the bony spur, resect the spinal cord lipoma, and section the fatty filum terminale.

LESSONS

Removal of the bony or fibrous septum and intradural lipoma and sectioning of the fatty filum terminale are required for effective detethering. Careful lipoma debulking, which can be facilitated with a CO₂ laser, must be performed while developing surgical planes and minimizing tension on the tethered cord.

https://thejns.org/doi/10.3171/CASE25691

Split cord malformations (SCMs) are a form of spinal dysraphism characterized by duplication of the spinal cord, often presenting with signs and symptoms of spinal cord tethering including leg weakness, back pain, urinary urgency or incontinence, and scoliosis.^1,2 In type I SCMs, the duplicated spinal cords are enclosed in dural sacs, and a rigid bony spur separates the two hemicords. Type II SCMs have a single dural sac and a nonossified fibrous structure separating the two hemicords.² While SCM is associated with abnormalities such as club foot and neurenteric cysts, SCMs have also been reported to rarely occur in conjunction with spinal cord lipoma.^3–6 Lipomas have been reported in cases of both type I and type II SCMs and can be associated with either or both hemicords.^3–6 SCMs and dorsal lipomas are thought to result from distinct embryological mechanisms, with SCMs originating after formation of a neurenteric canal that divides the neural plate and dorsal lipomas originating from premature disjunction during primary neurulation.^2,7 The presence of lipoma creates special considerations and challenges for surgical management of SCM and for effective release of the tethered cord.

Illustrative Case

A 37-year-old male with no significant past medical history presented with 1 year of low back pain that had been progressing over the previous 3 months, along with new lower extremity weakness and difficulty walking. He reported 1 week of burning pain in the right groin and urinary urgency. His physical examination demonstrated greater weakness of the right leg along with a dimple and tuft of hair in the midline over the lumbar area, above the level of the gluteal cleft. Imaging studies demonstrated multiple congenital vertebral anomalies (Figs. 1– 3), including a fusion of the L2–4 vertebral bodies and a type I SCM from level L1 to L4, with the two hemicords fusing at L4 and sharing a fatty filum terminale starting at that level. In addition, there was a dorsal defect involving the posterior elements with a lipoma extending from the subcutaneous tissues to the spinal cords. Finally, there was spinal canal stenosis at L3–4 and multilevel bilateral foraminal narrowing in the lumbosacral spine, and fatty infiltration of the filum terminale. Hydromyelia was present at T12–L1. Excision of the bony spur, lipoma resection, and sectioning of the filum were recommended to untether the spinal cord (Video 1).

FIG. 2.

Preoperative axial T2-weighted MR images rostral to (A), at the level of (B; indicated in the sagittal image [Fig. 1] as a horizontal line), or caudal to (C) the level of the bony spur. The hemicords were attached to each other both above and below the spur. This added to the complexity of the case, as the cords could not be mobilized, and this prevented access to the anterior-most aspect of the bony spur.

FIG. 1.

Preoperative sagittal T2-weighted (left) and T1-weighted (right) MR images of the lumbar spine.

FIG. 3.

Preoperative sagittal (left) and axial (right) CT scans of the spine.

VIDEO 1. Intraoperative video with narration describing course of resection of lipoma and excision of bony spur. Click here to view.

A standard approach in the prone position was used to access the lumbar spine. The fascia was divided from L2 to L5 and the paraspinal muscles reflected laterally. An abnormal fused posterior element mass was identified extending from L2 to L4. A partial defect through the inferior portion of the fused bone was also noted, through which the subcutaneous lipoma extended into the spinal canal. Using a high-speed drill, we thinned and removed the posterior elements, allowing visualization of the dura at the superior edge. The bony removal was extended in the inferior direction until we could identify the midline bony septum at L3. This was left in place as the surrounding bone was removed and the exact location of the intraspinal lipoma was identified. The lipoma could be seen entering the dura in a defined area inferior to the bony septum.

The dura was opened in the midline rostral to the bony spur, continued on the left side of the septum, and then extended inferiorly toward the lipoma. Once the dura was opened below the lipoma, the nerve roots of the cauda equina were seen within the subarachnoid space. The dura was then opened on the right side of the lipoma, and at this point the lipoma was entirely detached from the dura. Using direct stimulation, the right and left hemicords were identified and the stimulation threshold for motor responses was determined, which was between 0.1 and 0.3 mA. The dorsal portion of the lipoma was stimulated, and no clear activation was noted, so the extradural component of the lipoma was resected, allowing better visualization of the intradural structures.

The bony septum was thinned with rongeurs and a high-speed drill. The dural layers were separated from the bony septum, and a penetrating artery within the septum was identified and coagulated. During removal of the septum, there was direct contact with the right hemicord, resulting in a decrement in motor evoked potentials for some of the muscle groups. The left side was unaffected. Using microdissectors and a high-speed drill, we gradually removed the bony septum.

The two hemicords could then be visualized leading toward the intradural lipoma, and it initially appeared that the lipoma involved both hemicords. The intradural lipoma did not stimulate except at high thresholds with a flexible monopolar stimulator. Using a CO₂ laser, we removed the dorsal portion of the lipoma in a piecemeal fashion. The CO₂ laser is an ideal tool in this situation since it has both a hemostatic and a tissue debulking effect, the latter of which is accomplished with minimal movement or retraction of the spinal cord. At this point, the lipoma was noted to be adherent to the left hemicord but could be separated from it. There was also a remaining bony fragment and dural component that were adherent to the left hemicord. This fragment and the dural layers were removed. The fatty filum terminale was identified and, after being distinguished from the nerve roots via direct stimulation, sectioned. The spinal cord at this point was completely untethered. The pial edges were approximated using 6-0 PDS sutures, and a primary dural closure could be achieved. A standard closure of the soft tissues was performed, and an epifascial drain was left in place. Neuromonitoring on the left side remained at baseline. On the right side, there was preservation of the iliopsoas muscle and partial return of distal groups (tibialis anterior and gastrocnemius).

Following surgery, the patient had more pronounced right leg weakness, more significant proximally, and was admitted to inpatient rehabilitation. His back pain and urinary symptoms fully resolved, he retains full intact sensation, and he was noted to completely void his bladder on a complex uroflow study. By 7 months of follow-up, his right leg weakness was still present but had improved, and he is ambulatory with a cane. He has developed persistent pain distal to his right knee, and he continues to receive physical therapy.

Informed Consent

The necessary informed consent was obtained in this study.

Discussion

Observations

Abnormalities of neural tube formation lead to a spectrum of conditions from myelomeningocele to spinal cord lipomas and dermal sinus tracts, commonly involving a defect in the posterior elements, and are thought to occur due to an error in primary neurulation.^7,8 Conversely, SCMs are thought to arise from segmental anomalies during gastrulation.² In this case, there is a combination of events leading to both a SCM and a lipoma.

SCMs encompass a range of congenital spine malformations with the common feature of split or duplicated hemicords separated by a bony spur or fibrous band. In one large retrospective study, SCM was seen to occur most commonly at the level of the lumbar spine, and associated scoliosis and foot deformities were common, occurring in 50% and 48%, respectively.⁹ While SCMs are associated with multiple abnormalities, associated spinal cord lipomas are relatively rare. When present, the lipoma and SCM can exist in a number of configurations. Both Jamaluddin et al. and Pang et al. report cases of a type II SCM with lipomas attached to each hemicord.^{2, 3} Murakami et al. and Am et al., as in our case, each report cases of type I SCM with lipomas involving just one hemicord.^{5, 6} While the rarity of this configuration makes general conclusions unreliable, the different patterns of lipoma formation for type I versus type II SCM could reflect aspects of their embryological origin. Pang et al. postulate that both type I and type II SCM have a common embryological origin based on an abnormal neurenteric canal that bisects and divides the neural plate.² Mesenchyme condenses around this defect, creating an endomesenchymal tract that gives rise to associated defects.² The lipoma configuration could therefore reflect a difference in the timing of defect formation or be a consequence of the structural nature of the defect at that time.

It is worth considering if such an arrangement reflects two separate superimposed embryological events, or if the SCM and lipoma derive from a single insult. Dorsal lipomas are thought to result from premature disjunction of the cutaneous and neural ectoderms during primary neurulation, before the neural folds have fully closed to form the neural tube. This leaves a gap through which paraxial mesenchyme can migrate, which then differentiates into fatty tissue.⁷ According to Pang et al., typical lipomas in SCM are separable from the hemicords, reflecting adipose tissue deposited on the hemicords as likely remnants of the endomesenchymal tract, rather than from mesenchyme migrating through a neurulation defect.² The lipoma in this case, however, extended into the left hemicord, and therefore could reflect a separate embryological insult: first, formation of a neurenteric canal bisecting the neural plate, resulting in the SCM, and second, premature disjunction of one of the hemineural plates, allowing for mesenchymal invasion as found in typical spinal cord lipomas. This sequence of events could account for the rarity of this anatomical anomaly, although given the other similar case report, it is possible that the defect resulting in SCM predisposes the resulting divided neural plates toward premature disjunction.

The presence of two distinct congenital anomalies in this case highlights the technical challenges of this surgery. The patient experienced resolution of back pain and urinary symptoms. However the patient’s course was complicated by right leg weakness, which was concordant with changes in neuromonitoring intraoperatively. The primary consideration in this procedure is the tethering of the spinal cord by both the bony spur and the lipoma. The spinal cord is under tension and constrained in terms of movement, with an increased vulnerability to injury even with relatively gentle manipulation. In this case, the bony septum was removed first through an extradural approach. Once the posterior portion of the bony septum was removed, the dura was opened over each of the dural sleeves, allowing exposure of the two hemicords. Removal of the lipoma was then performed using a CO₂ laser, which minimized manipulation of the hemicords. The most ventral portion of the bony spur could not be removed since the spur was directed in an inferior direction with the two hemicords rejoined inferior thereto. Nonetheless, this portion of the spur was not directly in contact with the remaining hemicords. Finally, the thickened filum terminale was also identified and sectioned.

Lessons

SCMs can co-occur with lipomas, and patients may remain asymptomatic into adulthood, and symptoms may present without a clear preceding incident. Removal of the septum, the lipoma, and any fatty filum are all required in order to achieve an effective detethering of the hemicords.

Disclosures

Dr. Alan reported personal fees from J&J/DePuy, Stryker Instruments, SeaSpine/Orthofix, ATEC, Globus Medical, Spineart, and Induce Biologics outside the submitted work.

Author Contributions

Conception and design: all authors. Acquisition of data: Wozny, Gupta. Analysis and interpretation of data: Wozny, Alan, Gupta. Drafting the article: Baumgartner, Wozny. Critically revising the article: all authors. Reviewed submitted version of manuscript: Wozny, Alan, Gupta. Approved the final version of the manuscript on behalf of all authors: Baumgartner. Statistical analysis: Wozny. Study supervision: Gupta.

Supplemental Information

Videos

  Video 1. https://vimeo.com/1153636866.

Correspondence

Michael E. Baumgartner: University of California, San Francisco, CA. michael.baumgartner@ucsf.edu.