A rare case of split cord malformation type II with concomitant myelocystocele: illustrative case

Abstract

BACKGROUND

Split cord malformation (SCM) and myelocystocele (MC) are rare forms of spinal dysraphism arising from aberrant embryogenesis at distinct developmental stages. Although both lesions share embryological origins, their concomitant occurrence is exceedingly uncommon.

OBSERVATIONS

The authors report the first case of a type II SCM coexisting with an MC in an infant. The patient underwent microsurgical detethering and repair of the MC. Postnatal postoperative MRI revealed a type II SCM of the thoracolumbar spine. At 17 months, the patient demonstrated neurological symptoms consistent with spinal cord tethering and was brought back to the operating room for a complex detethering procedure with the assistance of the plastic surgery team and intraoperative neurophysiological monitoring. At the 2-year follow-up, the patient demonstrated stable spinal anatomy and improved functional outcomes. Genetic testing identified a variant in the GLI2 gene, suggesting a potential role for midline developmental gene perturbations in complex dysraphic syndromes.

LESSONS

This case expands the spectrum of closed spinal dysraphism, highlighting that errors in gastrulation and secondary neurulation can co-occur. Comprehensive preoperative imaging, high-resolution postnatal MRI, multidisciplinary coordination, and consideration of genetic evaluation are essential when managing complex spinal dysraphism. Awareness of such rare lesion combinations informs both surgical planning and developmental understanding of spinal cord malformations.

https://thejns.org/doi/10.3171/CASE26552

Split cord malformations (SCMs) are uncommon forms of spinal dysraphism in which the spinal cord is longitudinally divided into two hemicords. Pang’s embryological model proposes that during the very primitive stages of embryogenesis an accessory neurenteric canal is formed by an adhesion between the midline ectoderm and endoderm that bisects the notochord and primitive neural tube.¹ If the adhesion persists, this results in the development of a hemineural tube and hemi-notochord. Within the remnants of the accessory neurenteric canal, the mesenchymal tissue determines whether a rigid osseocartilaginous septum (type I) or a pliable fibrous raphe (type II) separates the hemicords.¹ Population-based data place the birth prevalence of SCMs between 4 and 6 per 10,000 live births, representing roughly 4%–5% of all spinal cord anomalies.² Either subtype can present with symptoms of tethering, orthopedic deformity, or cutaneous markers.

Myelocystoceles (MCs) are another type of rare spinal dysraphism that can be classified as terminal or nonterminal. Terminal MC is a skin-covered, lumbosacral spinal dysraphism characterized by an elongated caudal spinal cord with a syrinx involving the neural placode creating a “trumpet morphology,” which is attached to subcutaneous fat underlying the skin.³ Current developmental models suggest that terminal MCs arise during secondary neurulation after an apoptosis failure during the late degenerative phase of medullary cord formation. This failure of canalization of the medullary cord prevents the normal regression of the terminal cord and allows for ongoing CSF pulsations to balloon outward, thus creating a hydromyelic segment. Terminal MCs account for only 4%–8% of occult lumbosacral dysraphisms, but they are likely underrecognized. Nonterminal MC, on the other hand, is a rare spinal dysraphism involving a location other than the caudal end of the spinal cord. Rossi et al. described two subtypes of nonterminal MCs: the abortive and complete forms.⁴

Although SCMs and MCs share a common lineage of aberrant embryogenesis (albeit at different phases of development), their concomitant appearance seems to be exceedingly uncommon. However, a challenge in synthesizing the literature on SCMs and MCs is the substantial evolution and inconsistency in nomenclature over time. Historical terms such as “diastematomyelia” and “diplomyelia” were often applied imprecisely, frequently conflating distinct embryological entities or grouping heterogeneous lesions under a single label. Similarly, cystic dysraphic lesions have been described inconsistently, including terms such as “hydromyelic meningocele,” “hydromyelocele,” or “lipomyelocystocele.” These shifts in terminology complicate systematic literature searches and may obscure true associations between lesion types. Many earlier reports likely describing similar lesions are difficult to interpret due to the use of obsolete or overlapping terminology that predates modern embryological frameworks, potentially leading to underrecognition of specific lesion combinations. For the purposes of this review, a PubMed search (1950–March 2026) using the keywords “split cord malformation,” “diastematomyelia,” “terminal myelocystocele,” and “myelocystocele” identified isolated reports of type I SCM-associated MCs and composite dysraphisms involving multiple SCM subtypes with dorsal cysts, as well as a single case of diastematomyelia with a “lipomyelocystocele” arising from one hemicord.^5–9 No prior publication has described a true type II SCM accompanied by an MC.

Within the limitations described above, we present the first documented case of an infant with a type II SCM and a concomitant MC. Beyond adding to the spectrum of complex closed spinal dysraphism, this report underscores the need for high-resolution imaging and meticulous operative strategy when multiple embryologically linked lesions coexist.

Illustrative Case

Fetal Imaging

A 25-year-old woman was referred to the Cincinnati Fetal Care Center for further evaluation of a suspected fetal spinal dysraphism. Repeat fetal ultrasound (FUS) and fetal MRI studies were performed at 25 weeks 3 days of gestation as part of the evaluation. FUS and MRI demonstrated a closed lumbosacral spinal dysraphism with a sac with a “cyst within a cyst” appearance, most likely reflecting an MC. There was also kyphoscoliosis of the lumbosacral spine, suspicious for underlying segmentation anomalies. On visualization of the brain, there was dolichocephaly with a cephalic index of 67.9% on FUS, without a “lemon sign.” A “banana sign” on the FUS was present without ventriculomegaly. Fetal MRI confirmed the presence of hindbrain herniation with effacement of the fourth ventricle, without additional brain anomalies. Extra-cranial fetal anomalies identified on fetal MRI and FUS included a solitary kidney with crossed-fused renal ectopia, a single umbilical artery, and right talipes equinovarus (Fig. 1).

FIG. 1.

Fetal images obtained at 25 weeks 3 days of gestation. A: Axial FUS image of the posterior fossa demonstrating the appearance of the cerebellum (arrows) wrapping around the brainstem (banana sign). B: Parasagittal ultrasound image of the spine demonstrating lumbosacral spinal dysraphism with a sac with a “cyst within a cyst” appearance (arrow) consistent with an MC. Note the sac wall is relatively thick, compatible with a closed or skin covered spinal dysraphism. C: Sagittal T2-weighted single-shot fast spin-echo (SSFSE) MR image of the fetal brain and spine demonstrating effacement of the fourth ventricle and hindbrain herniation (solid arrow) with a lumbosacral myelomeningocele (dashed arrow). D: Axial T2-weighted SSFSE MR image obtained at the level of the abdominal cord insertion, demonstrating SCM (white arrows; only identified in retrospect) and the MC sac (black arrows). E: Axial T2-weighted SSFSE MR image of the lower abdomen demonstrating a trumpet morphology of the neural elements in the spinal dysraphism sac (arrow) consistent with an MC.

Postnatal Course

The male neonate was born via spontaneous vaginal delivery at 38 weeks 5 days of gestation, with a birth weight of 3.2 kg. Examination demonstrated a broad, skin-covered lumbosacral mass with a very thin area of skin coverage in the middle of the mass, measuring approximately 6.0 × 3.5 cm with a tuft of vellus hair consistent with an MC, right talipes equinovarus, and moderate thoracolumbar kyphoscoliosis (Fig. 2). The lower extremity motor examination noted hip flexion, knee flexion, and weak ankle movements bilaterally, left greater than right. Immediately after birth and prior to neurosurgical consultation, the patient was started on empiric antibiotics by the neonatal team owing to concern for a markedly thinned area of skin coverage at the dome of the mass, and had the lumbosacral mass covered with a sterile dressing, although no egress of spinal fluid was noted. He was taken to the operating room on day of life 2 for microsurgical repair and detethering of the MC.

FIG. 2.

.Postnatal clinical photographs (Apple iPhone 12 Pro Max) obtained on day of life 0. A: The lumbosacral mass is broad based, slightly right eccentric, and fully skin covered. The dome has areas of dysplastic, thin, and discolored skin. There was no evidence of dehiscence or fluid leakage. B: The lesion measured approximately 3.5 × 6 cm.

Initial Operative Management

The patient was brought from the NICU, placed under general anesthesia, positioned on gel rolls, and prepped and draped in standard fashion. A midline incision was made cranial to the cyst. Subperiosteal dissection was completed to expose the most caudal intact lumbar spinous process and adjacent laminae. A very minimal partial inferior laminectomy and spinous process removal were performed. The ligamentum flavum was undermined, epidural fat was removed, and the normal thecal sac was identified. This was followed several millimeters caudally until it entered the MC. Transitional skin blending into the cyst wall was resected circumferentially. Two large septated cysts and two smaller daughter cysts were sharply dissected free along their walls to the point of attachment at the placode. The cyst wall was meticulously peeled off tethered nerve roots at the base of the placode. Wide lateral epidural dissection yielded generous dural flaps. The splayed dura was reapproximated into a spacious tubular thecal sac. Paraspinous muscles and lumbodorsal fascia were elevated subperiosteally from the dysplastic sacral laminae until mobile. Bilateral advancement allowed primary myofascial closure, followed by primary skin closure.

Postoperative Imaging

Postoperative MRI of the spine was obtained at day of life 8 that demonstrated postoperative changes from spinal dysraphism repair with a postoperative air and fluid collection dorsal to the lumbosacral spine. There were multiple segmentation anomalies, focal kyphosis, and deficiency of the dorsal osseous elements of the thoracolumbar spine from approximately the T11 level inferiorly. The sacrococcygeal spine appeared hypoplastic; however, it was present. Most notably, there was an SCM of the thoracolumbar spinal cord beginning at the T6 level without an associated bony cleft. The hemicords were elongated, terminating in close approximation to each other in a skin-covered sac with expansion of the surrounding meninges compatible with lipomyelomeningocele (Fig. 3). Follow-up spine MRI at 4 months of age demonstrated interval resolution of the previously seen postoperative fluid collection with a new spinal cord syrinx in the ­mid-thoracic and left hemicord (Fig. 4). Follow-up MRI studies performed at 8 months and 14 months of age continued to remain stable.

FIG. 3.

Postnatal MR images obtained after repair on day of life 8. A: Sagittal T2-weighted fast spin-echo (FSE) MR image of the spine demonstrating postoperative fluid collection dorsal to the thoracolumbar spine (solid arrow) and focal kyphosis of the lumbar spine (dashed arrow). B: Axial T2-weighted FSE MR image demonstrating SCM (dashed arrows) and overlying postoperative fluid collection (solid arrow). The arrowhead indicates the right kidney for reference. C and D: Coronal T2-weighted FSE MR images demonstrating the right hemicord (C, arrow) and left hemicord (D, arrow) exiting the spinal canal and terminating in a skin-covered sac very close to one another, consistent with coexisting lipomyelomeningocele.

FIG. 4.

Follow-up MR images obtained at 4 months of age. A: Conoral T2-weighted FSE MR image of the spine demonstrating lower thoracic and lumbar segmentation anomalies with associated kyphosis (arrow). B: Sagittal 3D balanced fast field echo/FIESTA MR image of the spine demonstrating a new spinal cord syrinx (arrow). Note the interval resolution of the previously seen postoperative fluid collection.

Postoperative Clinical Course After Initial Surgery

At 11 months of age, the patient clinically began to demonstrate clear significant asymmetric weakness of the right lower extremity compared to the left and was also noted to be wet between intermittent catheterizations. His interval manual muscle test completed around 12 months of age demonstrated decreased function with flaccid right lower extremity and low lumbar deficits in the left lower extremity with foot dorsiflexion present. Given the progression of neurological deficits, surgical intervention was recommended for detethering of the right hemicord and associated lipomyelomeningocele.

Subsequent Detethering Procedure

At 17 months of age, the patient was brought into the operating room, placed under general anesthesia, and underwent complex detethering, lipomyelomeningocele debulking, and wound closure with assistance from the plastic surgery team. The patient was positioned prone, and intraoperative neurophysiological monitoring including somatosensory evoked potentials (SSEPs), motor evoked potentials (MEPs), and both free-running and triggered electromyography (EMG) of the lower extremities and sphincters was performed. Baseline upper extremity SSEPs were robust; lower extremity SSEPs were nonreproducible. Notably, bulbocavernosus reflexes were absent bilaterally. The prior midline surgical incision was reopened, and dense scar and lipomatous tissue were immediately encountered. This tissue was debulked with eventual identification of the prior dural sutures placed from the previous closure. The bony anatomy was dysraphic with the absence of a lateral bone on the right and a known underdeveloped left bony sacrum. Under high magnification, the dural edges were tented to expose the right and left hemicords. There was a thick fibrous septum noted with a central midline artery. A Prass probe identified functional nerve roots that had right-sided roots that traversed medially to exit on the left to supply the right leg and right-sided sphincters. Although there were bilateral motor responses on the left and right legs, there was no noted movement and clinically significant atrophy of the right leg. The terminal dorsal roots that traversed into the lipomyelomeningocele on the left had no motor significance and were coagulated and cut. The left hemicord was noted to be tethered superiorly to the dura along with the exiting nerve roots. Motor stimulation in this area demonstrated sphincter tone and activity in the left leg. After thorough investigation of all possible sites of tethering, the intradural space was closed primarily. Plastic surgery assisted in the complex wound closure and local tissue rearrangement. Figure 5 depicts intraoperative photographs of the complex detethering procedure.

FIG. 5.

Intraoperative microscopic images obtained during the detethering procedure and postoperative MR images obtained at 2 years. A: Spinal canal prior to lipoma debulking, demonstrating the complex arrangement of the exiting nerve roots and lipomatous tissue. The rostral direction is noted with an asterisk in all microscopic images. The right hemicord (black block arrow) and its exiting nerve roots are deeply interwoven with lipomatous tissue (dashed black arrow). B: Prior to detethering, the right hemicord (black block arrow) was noted to course directly over the left hemicord. The right-sided dorsal nerve roots (thin black arrow) were seen coursing toward the left. C: The left hemicord (white block arrow) demonstrated exiting nerve roots (thin white arrow) with overlapping terminal nerve roots of the right hemicord (black block arrow). The right hemicord demonstrated dorsal nerve roots that terminate into the lipomyelomeningocele (thin black arrow). D: After completion of detethering, the right hemicord (black block arrow) terminated in residual lipomyelomeningocele that abuts the right lateral dural edge. The nonfunctional right-sided dorsal nerve rootlets were removed. The left hemicord (white block arrow) is seen along the left dural edge. E: Sagittal T1-weighted MR image of the lumbar spine obtained at 2 years of age, demonstrating mild interval decrease in size of spinal cord syrinx (white arrow). F: Axial reformatting of the 3D balanced turbo field echo MR image, obtained from the same examination, again showing the two hemicords (black arrows) within the spinal canal, consistent with SCM.

Postoperative Course

Postoperatively, the patient was kept supine for 72 hours in the intensive care unit to prevent formation of a pseudomeningocele and completed a 7-day dexamethasone taper. Recovery was uncomplicated, and the patient was discharged home on postoperative day 5. At the time of discharge, the patient was at his neurological baseline relative to his preoperative examination. At the 3-month postoperative follow-up, the wound was well healed. Neurologically, he has continued to progress with therapies and is able to stand with assistive devices with an L1 sensory level on the right and S1 sensory level on the left. Two-year follow-up MRI demonstrated stable hemicord configurations and thoracic cord syrinx (Fig. 5E and F).

Informed Consent

The necessary informed consent was obtained in this study.

Discussion

Observations

This is the first documented coexistence of a type II SCM and a concomitant MC and lipomyelomeningocele. This case highlights a rare example of the clinical sequelae of gastrulation and secondary neurulation errors. The coexistence of these malformations defies the traditional expectation that these embryological processes fail independently and instead suggests a possible unusual cascade of midline developmental errors. Additionally, the SCM was not prospectively identified on fetal MRI or at initial surgical repair, although it was identified in retrospect (Fig. 1) on postnatal imaging, which illustrates the inherent limitations of fetal imaging. A postnatal MRI study prior to surgical intervention was not obtained; while it may not have influenced the immediate management strategy, it would have been helpful in more confidently characterizing the nature of the MC (terminal vs nonterminal complete form).

The extremely low incidence of combined SCM and MC is reflected in the scant literature. Our review found no prior reports of a type II SCM accompanied specifically by an MC. Parmar et al. described the case of a 4-month-old girl with diastematomyelia (SCM) and a “terminal lipomyelocystocele” arising from one hemicord.¹⁰ This patient had similar multisystem findings including an ectopic kidney and partial sacral agenesis. There are also rare examples of composite dysraphism in which an SCM co-occurred with other cystic malformations, although none mirror our case directly. For instance, Khandelwal et al. reported on a child with multilevel SCMs (both types I and II at different levels) associated with a dorsal spinal cyst and other anomalies.⁵ In contrast to those composite cases, our report is the first to highlight a true type II SCM with a concomitant MC, expanding the spectrum of closed spinal dysraphism. This combination reveals that when an error of gastrulation (resulting in an SCM) is present, a subsequent failure in canalization during secondary neurulation can still occur. Such observations reinforce that multiple embryonic insults can happen sequentially or in tandem, producing complex tethering pathologies that challenge surgical management.

Genetic screening of this patient revealed a variant of uncertain clinical significance of the GLI2 gene (c.2287G>A mutation). The GLI2 protein is part of a family of very large polymorphic proteins located on 2q14.2.¹¹ It is a zinc finger activating transcription factor of the SHH (sonic hedgehog) signaling pathway, which plays a crucial role in the development of the diencephalon and distal extremities during embryogenesis. Homozygous deletion of both GLI1 and GLI2 can cause complete absence of the pituitary gland.¹² Heterozygous mutations of the GLI2 gene cause a variety of clinical phenotypes, ranging from asymptomatic cases to more severe clinical phenotypes and holoprosencephaly (HPE) or HPE-like syndrome. Although this specific allelic aberration has not been clearly identified as pathogenic, its presence is intriguing given the array of midline abnormalities (spinal dysraphism, vertebral segmentation defects, renal agenesis) in this infant. Disruption of the SHH-GLI signaling axis could contribute to such multifocal developmental errors. Indeed, animal models support the concept that SHH pathway aberrations can produce complex malformation syndromes: mice engineered with GLI2 and GLI3 gene disruptions exhibit the full spectrum of VACTERL (vertebral defects, anal atresia, cardiac defects, tracheo-esophageal fistula, renal anomalies, and limb abnormalities)–like anomalies.¹³ While a causal link cannot be confirmed in our single case, the genetic finding raises the possibility that an underlying developmental gene variant affecting midline axis formation lowered the threshold for this rare combination of dysraphic errors. Future investigations into such patients, including genetic analyses and animal modeling, may clarify whether occult spinal dysraphism like SCM with MC has any definable genetic predisposition.

Lessons

This case offers several important clinical practice lessons. First, in any patient with an occult spinal dysraphism or unusual cutaneous lumbosacral finding, complete neuraxial imaging should be obtained, when clinically feasible, prior to surgical intervention. Even when a single lesion seems evident, the entire spinal axis should be evaluated for additional anomalies. Detecting a coexistent SCM presurgery would have informed parental counseling and potentially altered intraoperative management of the MC. Fetal imaging, which was obtained twice in our case, hinted at multiple anomalies (vertebral and renal abnormalities), yet the diagnosis of SCM was elusive until postnatal MRI was performed. Clinicians should maintain a high index of suspicion for occult pathologies in any complex or atypical spinal lesion and pursue high-resolution postnatal imaging accordingly. In this case, the decision to forgo a preoperative postnatal MRI study was influenced in part by concern that positioning the infant on the friable, attenuated skin overlying the mass risked pressure-related breakdown; although such imaging could likely have been obtained with careful positioning, it was not believed at the time to be necessary to guide immediate management. In retrospect, it may have allowed prospective identification of the coexisting SCM, informed parental counseling, and potentially refined the intraoperative approach. We acknowledge the absence of a preoperative MRI study as a limitation of our management.

Second, the surgical management of combined dysraphic lesions is not standardized; it demands meticulous neurosurgical technique, but is greatly enhanced through collaborative multidisciplinary expertise. Intraoperative neurophysiological monitoring proved invaluable during the detethering; our team utilized SSEPs and MEPs as well as EMG to map functional nerve roots and avoid unnecessary injury. The SCM anatomy meant that nerve root trajectories were atypical (with right-sided roots crossing midline to exit toward the left), making neuromonitoring crucial to prevent misidentification of functional neural tissue. After extensive scar and fat resection, our plastic surgery colleagues were still able to achieve a robust, multilayer closure.

This case is unique in that we have long-term follow-up spanning through the prenatal period with ultrasound and MRI, immediate postnatal and postoperative studies, and serial follow-up through 2 years of age. This longitudinal documentation permits observation of the lesion’s natural history. Notably, although follow-up imaging at 4 months demonstrated the SCM and an interval syrinx, prophylactic detethering was not pursued at that time. The patient was making meaningful clinical progress, had competing medical and orthopedic priorities, and the role of prophylactic detethering in a clinically improving child remains controversial when balanced against the operative risks of a complex reoperative field. Following serial examinations and repeated risk-benefit discussions with the family, surgery was reserved for objective neurological deterioration, which ultimately manifested and prompted intervention at 17 months.

Finally, this case highlights the potential value of genetic and developmental investigation in patients with rare or unexplained malformations. Our patient’s constellation of findings—SCM, MC, hemivertebrae, and unilateral renal agenesis—suggests a broader midline developmental field defect, possibly aligning with known associations (e.g., VACTERL spectrum). While the identification of the GLI2 variant in our patient did not directly alter acute management, we hope that through genetic banking and targeted gene analysis, future insights into developmental biology can be derived.

The principal contribution of this report is not the rarity of the combination alone, but the operative and diagnostic lessons it affords, namely the necessity of complete preoperative neuraxial imaging, the reliance on neuromonitoring where SCM produces aberrant root trajectories, and the potential role of genetic evaluation in midline developmental field defects. Clinicians should obtain complete preoperative imaging of the spine (and other systems as indicated) to guide surgical planning and be prepared with multidisciplinary resources for complex repairs. Moreover, obtaining genetic evaluations in such patients may help to advance our understanding of the underlying embryogenesis of spinal cord malformations.

Acknowledgments

Generative artificial intelligence large language models (Claude 4) were used in the preliminary drafting of the manuscript. After significant substantive editing, this final draft was reviewed for accuracy and reflects our original ideas.

Disclosures

The authors report no conflict of interest concerning the materials or methods used in this study or the findings specified in this paper.

Author Contributions

Conception and design: Patel, Owen, Ivey, Nagaraj. Acquisition of data: Patel, Owen, Ivey, Nagaraj. Analysis and interpretation of data: Patel, Owen, Nagaraj. Drafting the article: Owen, Ivey. Critically revising the article: all authors. Reviewed submitted version of manuscript: all authors. Approved the final version of the manuscript on behalf of all authors: Patel. Study supervision: Patel.

Correspondence

Smruti K. Patel: Cincinnati Children’s Hospital Medical Center; University of Cincinnati College of Medicine, Cincinnati, OH. smruti.patel@cchmc.org.