Cervical Split Cord Malformations: A Systematic Review
Correspondence Address: Source of Support: None, Conflict of Interest: None DOI: 10.4103/0028-3886.299132
Source of Support: None, Conflict of Interest: None
Keywords: Cervical spine, diagnosis, split cord, treatment
Whereas there is a decreasing trend in the incidence of neural tube defects in the world, it has been increasingly reported from the Indian subcontinent due to the widespread availability of MRI and active surveillance of scoliosis patients being referred for treatment. The oldest preserved bony specimen of diastematomyelia is that of a 20-year old found at a burial tomb at the Negev desert of Israel and dates back to 100 AD. Perret describes that autopsy reports as early as 1684 AD have detailed this condition in stillborn fetuses and monsters. Ollivier described the earliest case of sagittal splitting of the spinal cord and named the condition diastematomyelia from Greek, diastema – cleft and melos – medulla., Diastematomyelia is the term used to describe a congenital cleft or splitting of the spinal cord, each portion of which may be invested in a separate arachnoid sheath under a common dura or may have separate dural sheaths as well. Hertwig in 1892 was the first to experimentally produce this malformation in frogs by delaying the fertilization of the ovum., von Recklinghausen coined the term diplomyelia to describe a completely formed spinal cord situated anteriorly or posteriorly to the original cord. Herren and Edwards defined the term diplomyelia (Greek dipulo - double) to include any complete duplication of a spinal cord segment. Hamby (1936) is credited as the first surgeon to have operated on a living patient with diastematomyelia. Pang et al. suggested a new classification to deal with all double spinal cord malformations and used the phrase “Split Cord Malformations”(SCM) to describe the entire spectrum of anomalies associated.
Cervical split cord malformations are extremely rare pathology with only few cases reported till date. Till 1972, most of the 11 cases described were diagnoses made at autopsy with the earliest report by Fischer et al. in 1889. James et al. (1972) were the first to document the clinical picture in a 56-year-old woman with quadriplegia. Whittle et al. (1983) were one of the first to document the successful surgical outcome of spur excision and repair in a 2-year-old girl with Klippel Feil Syndrome (KF) who presented with posttraumatic paraparesis. There have been sporadic reports every year or two since then with the largest series reported by Mahapatra et al., (9 cases, 2011). Previously David et al. (7 cases, 1996) and Ulmer et al. (5 cases, 1993) had reported the presence of cervical SCM in patients of Klippel Feil syndrome. In this systematic review, we attempt to perform the qualitative analysis of the cervical split cord malformations reported in the literature.
The initial literature search was done using keywords “(split cord malformation OR SCM OR diastematomyelia OR diplomyelia) AND (cervical)” yielded 111 articles. On screening these articles, 46 relevant abstracts were retrieved, out of which only 38 accessible full articles in English language included cervical split cord malformation cases as shown in PRISMA flow diagram [Figure 1]. The qualitative analysis of these 38 reports has been summarized in [Table 1].
Age of presentation and sex prevalence
The clinical presentation of cervical spinal cord malformations has ranged from the newborn to as late as 56 years of age with approximately 50% cases (30 cases) presenting before the age of 10.,,,,,,,,,, As many as 23 cases have been reported in the adults over the age of 18.,,,,,,,,,,,,, A female preponderance is evident (M:F l 2:5). There is no explanation in literature for this predominance and as to why the female embryo is susceptible to defects in secondary neurulation.
Symptoms and signs
Neurological deficits are reported in at least 19 out of the 38 reports (individual cases are not described in large series). A near normal neurology has been seen in six out of the 38 reports.,,,,, Neural deficits range from a mild sensory disturbance to prolonged quadriplegia with bladder and bowel involvement. Neck pain and radiculopathy may be associated with underlying vertebral fusions and restricted motion., Gait disturbances, asymmetrical weakness, atrophy of lower limbs, neurotrophic ulcers, and incontinence are frequently seen. Neurotrophic ulcers and self-mutilation of fingers due to sucking and biting the anesthetic limb has been reported in cases of cervical SCM. Ohwada et al. reported the case of a 19-year-old male with C6-C7 SCM who presented with the signs of thoracic myelopathy.
Cutaneous stigmata are reported in as many as 60% cases in large series reported by Mahapatra et al. Hypertrichosis, naevi, dimples, dermal sinus, and lipomatous swellings are seen in many patients with SCM.,,
Associated features include torticollis, meningoceles, myelomeningoceles, KF syndrome (low-lying hair line with limitation of cervical movements, Sprengel shoulder, pterygium colli, and mirror movements of the upper limbs), and spinal deformities (kyphosis and scoliosis). Often, the routine workup for a spinal deformity correction surgery reveals a cord anomaly in a relatively asymptomatic patient. Cervical SCM that are not associated with other congenital anomalies typically become symptomatic in adult life following a trivial trauma to the extent that the discovery of a cervical SCM in the absence of a traumatic history is rather rare. Hemiplegia following trivial trauma is reported.
Although reported from all over the world, few reports have come from Japan, and the African nations, whereas large series have emanated from India,, and Turkey., Underdiagnosis and underreporting could be a reason or there could be unknown ethnic or environmental factors that are still to be unearthed.
The reports of cervical SCM have been too sporadic to discern a familial inheritance pattern.
According to Pang, the formation of an abnormal fistula through the midline embryonic disc is the embryological error leading to a SCM. This fistula maintains the communication between the yolk sac and amnion which makes a continued contact between the ectoderm and endoderm possible. This leads to the regional splitting of the notochord and the overlying neural plate. The surrounding pluripotent mesenchymal tissue condenses around the fistula to form an endomesenchymal tract that bisects the notochord and forces each overlying half to neurulate against its own hemicord.
The basic anomaly thus comprises two heminotochords and two hemineural plates separated by a midline fistula containing ectoderm, endoderm, and mesenchyme. Further evolution of this anomaly into final malformation depends on the ability of the hemicords and heminotochords to heal around the endomesenchymal fistula, the fate of the three germinal elements within this fistula, and the variable extent to which this fistula persists as well as the interaction between the heminotochord and the hemineural plates during neurulation [Figure 2].
Mahapatra and Gupta further state that the precursor meninges are the likely source of midline bone, apart from the formation of the dural tubes. After the formation of the dura, the precursor meninx on the side of the median dura that faces each hemicord forms a complete arachnoid tube and the precursor meninx on the side facing the midline forms the bony spur. The extent of the disappearance of the endomesenchymal fistula and the subsequent interaction of precursor meninges with the fistula determines the position of spur as this is probably genetically controlled. Many cases of cervical SCM are associated with Klippel Feil syndrome and other disorders of vertebral fusion and segmentation. The influence of homeobox genes Pax-1 and Hox are being investigated but the relationship between the genes affecting spinal cord division and primary segmentation as yet remains unknown. Chandra et al. postulated two mechanisms for the occurrence of a dorsal spur, a rare variant: (1) passage of an abnormal cell cluster dorsally with subsequent loss of contact with the ventrally situated cell cluster and (2) migration of cells around the hemicords and formation of passage between them in a dorsoventral direction.
The osseous/fibrous-cartilaginous septum anchors the spinal cord and impedes its normal ascension with growth of the skeleton leading to tethering of the cord. The plasticity of the nervous system allows for small children to remain asymptomatic for long. However, with growth spurt this plasticity is also rendered ineffective and patients become symptomatic. This tethered cord that is not normally floating in CSF space is further insulted by the coexisting spinal stenosis and deformity.,,
An asymmetrical distribution of blood supply to the hemicords and compression of the anterior spinal artery or veins leads to ischemic disturbances leading to symptoms., Yamada et al. were able to demonstrate the effect of traction on the vascular supply of the spinal cord of a cat using spectroscopy.
Hypoplasia of one or both of the hemicords may give rise to any of the symptoms encountered.
The literature on antenatal diagnosis of SCMs is sparse. There are isolated case reports reported in literature mentioning the use of antenatal sonogram and MRI for establishing the diagnosis.,,,,
Ultrasonogram is the screening tool of choice for the detection of suspected SCM and is superior to a plain radiograph in newborns. MRI is the definitive investigation of choice and can delineate the exact morphology of the cord and anomalies such as hemicords, syrinx, and intradural malformations such as fatty filum, teratomas/dermoids, lipomas, and cysts. A screening MRI of the whole spine is mandatory in all suspected cases to detect occult multisite dysraphisms., CT scan should be performed for highlighting the bony elements of the anomaly and their relationship with the cord, especially when associated with scoliosis or kyphosis. Conversely, all patients planned for spinal deformity correction should be screened for occult or overt spinal dysraphism before proceeding for surgery.
Role of urodynamics
A total of 60–75% patients with SCM have subtle or overt urinary tract dysfunction with the most common complaint being urge incontinence., They usually tend to stabilize or improve after surgery. Therefore, Perez et al. concluded that all patients with SCM should undergo a urodynamic evaluation prior to surgical intervention. It bears on prognosticating the postoperative outcome as well.
There are considerable controversies regarding the need for surgery in asymptomatic patients with no neurological deficits and SCM type II patients. David et al. reserved surgery only for those with overt spinal instability and progressive neural deficit. Only 1/7 cases in their series was operated. Zuccaro states that majority of the asymptomatic patients in her series were not operated and did well at 7 year followup. However Matson et al., Mahapatra et al., Proctor et al. have all suggested that the aim of the surgery should be prophylactic rather than curative and as such should be offered to asymptomatic patients as well. That the treatment of intraspinal anomalies prior to deformity correction results in better outcomes is a fact endorsed by most orthopedists and neurosurgeons who operate on spinal deformities., Surgery can lead to healing of trophic ulcers as well. Surgery is definitely indicated in every patient who presents with associated anomalies like dermal sinus, dermoids, teratomas, and cysts that can by themselves lead to complications if not treated appropriately.
Patients are operated in the prone position. Neurophysiological monitoring is desirable but depends on the availability of personnel and equipment. Intraoperative monitoring can give the surgeon greater confidence while dissecting and manipulating around the cord by urging him to stop dissection till the reduced amplitude of evoked potentials returns to baseline levels. The use of intraoperative image intensifier/X-ray is desirable to correctly localize the site of the lesion as cutaneous markers can be segments away from the actual lesion. A laminotomy or laminectomy with a high-speed drill is done and a Kerrison's punch (or a diamond drill) can be used to nibble out the spur completely before proceeding with detethering as needed. A laminoplasty is indicated for a large segment disease to prevent postlaminectomy kyphosis. Alternatively, pedicle screw fixation can be combined with the procedure, especially if deformity correction is done in the same sitting. The dural sleeve of the spur must be completely removed as there have been reports of new spurs arising from re-ossification along the remnant sleeve.,, Excision of the filum prevents any traction on the tethered segment or conus. This is done by a small sacral laminotomy in cases of cervical SCM.
For dorsally located spurs, a laminoplasty should never be performed for the fear of causing cord damage. A laminectomy one level above and one below the level of the spur is done. The spur is drilled off gradually in a dorsal to ventral direction and the dura is opened with a gentle curve encircling the spur. The durotomy is extended about two levels cephalad and caudad to the level of the lesion so that there remains sufficient dura for watertight closure. The bony spur is thinned out with a high-speed drill and the shell remaining is removed with microrongeurs. A watertight closure is done with 5-0 Vicryl or Nylon. The rest of the wound is closed in layers [Figure 3] and [Figure 4].
The results of surgery are generally gratifying with dramatic improvement in neurology to complete recovery of symptoms reported by many workers.,,,,,,,,, Persistent neural deficits or incomplete recovery are also reported in some cases with severe preoperative deficits.,,, A total of 7–10% patients may develop retethering over a period of 5 years due to reossification of the spur along any remnant dural sleeve.,, Mahapatra reported that none of the patients undergoing prophylactic surgery had postoperative neurological deterioration.
Overall, the complications of SCM surgery are low. Preoperative complications are related to distorted anatomy and difficulties with hemostasis and watertight dura closure. Mahapatra and Gupta subclassified Type I SCM [Figure 5] into 4 types based on the position of the bony spur causing the split [Figure 6]a, [Figure 6]b, [Figure 6]c, [Figure 6]d.
They found that the risk of inflicting trauma to the hemicords is highest in Type 1d, 4/6 patients in their series had post-operative deterioration. Urinary retention postsurgery, arachnoiditis, and infections are the reported complications which are managed conservatively.,
Cervical SCM is fortunately an exceptionally rare condition, with less than 75 cases documented in literature. MRI remains the investigation of choice. The controversy regarding prophylactic surgery in asymptomatic individuals remains. We advocate prophylactic surgery in all asymptomatic individuals to preclude severe neurological deficit following trivial trauma in the future. The results of surgery in asymptomatic individuals are excellent while those in symptomatic individuals are good as well. All cases undergoing orthopedic deformity correction surgeries should be routinely screened for cord anomalies to prevent inadvertent perioperative catastrophes.
The authors wish to thank Dr. S. Siva Chidambaram, Chief Librarian, Dr. B.B. Dikshit, Librarian, All India Institute of Medical Sciences for their help in procuring some of the lesser accessible references used in this review.
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Conflicts of interest
There are no conflicts of interest.
[Figure 1], [Figure 2], [Figure 3], [Figure 4], [Figure 5], [Figure 6]