Split Cord Malformation

General

There is no uniformly accepted nomenclature for malformations characterized by duplicate or split spinal cords.

Pang et al have proposed the following.

The term split cord malformation (SCM) should be used for all double spinal cords, all of which appear to have a common embryologic aetiology.

Definition

all double spinal cords that may be separated by a dural fibrous band or by bone.

Embryology

Normal

2nd wk

Bilaminar s(x)

Epiblast: Adjacent to Amnion
Hypoblast: adjacent to Yolk sac

Caudal midline cells form primitive streak

Rostral midline cells form primitive knot (Hensen's node)

2-3 wk process of gastrulation starts

Epiblast cell adjacent to the primitive streak migrate through the primitive streak and form the mesoderm

Now there is a trilaminar embryo

Day 16

Primitive streak begins to regresses so that the primitive knot occupies a progressively more caudal position within the embryonic disc.
At the same time, cells situated along the rostral lip of the primitive knot migrate between the epiblast and hypoblast and are gradually laid down as the notochordal process
Notocord is then canalized to form a tube that is now in communication with the amnion through the primitive pit.

3wk

Gastrulation ends

Formation of Primitive neurenteric canal:

Canalized notochordal process fuses with and opens through the underlying endoderm (intercalation) to complete a temporary passage through the embryo, which now joins the amnion and yolk sac.
Exist of 2-8 days
Final fate:

open notochord separates from the endoderm (excalation) and reforms a blind tube, thereby permanently obliterating the primitive neurenteric canal and the communication between the amnion and yolk sac

Abnormal

Pathology

Unified theory for the development of both types of SCM by Pang et al

An ontogenetic error occurred

When the primitive neurenteric canal closes
Formation of an accessory neurenteric canal though the midline embryonic disc

Maintaining communication between ectoderm and endoderm within the canal
This abnormal fistula --> regional splitting of the notochord and the overlying neural plate

The rest of the notochord is well formed and inducing the neural plate to roll up through the ascension of the neural crest cells to form the neural tube
Endomesenchymal tract formation

The abnormal fistula matures with the surrounding mesenchyme condensing around it + a "pinch" of endoderm protruding from the base of the fistula,
occupies the space between the split notochord and split neural plate
Mesenchyme has pluripotent ability: can form fibroblasts, cartilage, bone, blood vessels, fat, and myoblasts

The normal neurenteric canal has no Notochord splitting so does not produce a split cord malformation

Located

Variable
Lie rostral to the primitive neurenteric canal because the primitive pit into which the normal neurenteric canal opens, ultimately comes to lie opposite the coccyx. all known SCMs involve cord segments that are rostral to the coccyx.

Due to healing ability of the embryo:

The split notochord heals hence rarely see a bifid vertebral bodies
The endomesenchymal tract connecting the Gut to Skin rarely fully persist but remnants parts of the original tract remain in modified forms

Hypothetical steps in the formation of the endomesenchymal tract.

an accessory neurenteric canal (fistula) may begin as an ecto-endodermal adhesion where the two germ layers are in virtual contact in the midline. The midline neuroectoderm is thus bisected to give two hemineural plates.

each hemineural plate neurulates independently in relation to its own heminotochord.

condensation of mesenchyme around the midline fistula, still containing endodermal elements, forms the endomesenchymal tract. Further development of the midline mesenchyme partly determines the nature of the median septum.

cells from meninx primativa (primitive meninges) appearing between the hemineural tube and its heminotochord.
If meninx primativa cells surround both cord it will be type 2 if it surround each cord will be type 1

Anomalies of the overlying skin such as hypertrichosis (A, C) may signify the presence of an underlying anomaly.

(A) Abnormal connections with the overlying skin can be seen, referred to as dermal sinus tracts. Similarly abnormal connections can arise anteriorly, connecting the spine with the lumen of the gut or respiratory tract. Myelomeningocele manqué

(B) is a similar anomaly in which blood vessels and nervous cells form a midline septum. Several tumours are also believed related to this abnormal development (C).

Dermoid cysts and lipomas are two such tumours, and they are frequently found posterior to the spinal cord and may be associated with a split cord malformation, as in this case.

Clinical features

Types

T2-weighted image, axial plane, level of L2–L3, shows two hemicords separated by the chondro-osseous ligament, each in a separate dural sac.

T2-weighted image, axial plane, level of L2, shows a single dural sac containing both hemicords with appearance of the chondro-osseous ligament central in anteroposterior orientation.

SCM Type	1 (Diastematomyelia) ONE=BONE	2 (Diplomyelia)
Anatomical features	-Two hemicords in two dural sleeves -Separated by a midline bony spur. -Hypertrophic laminae are often fused to adjacent levels.	-Two hemicords in a single dural sleeve. -Separated and tethered by a fibrous band attached to the dura. -Each hemicord has nerve roots arising from it. -Usually no spine abnormality at the level of the split -usually spina bifida occulta in the lumbosacral region
Clinical presentation	-2/3 overlying skin abnormalities (nevi, hypertrichosis (tuft of hair), lipomas, dimples, or haemangiomas) -Orthopaedic foot deformity (neurogenic high arches).
Radiographic	CT - Bony spur - intersegmental fusion and adjacent spina bifida are virtually pathognomonic. - Other abnormalities of spine at the level of the split (dorsal hypertrophic bone where the median “spike” attaches MRI - two hemicords in separate subarachnoid spaces.	Two hemicords seen within a single subarachnoid space on T2-weighted MRI. High-resolution T2-weighted MR or CT myelography may show fibrous septum attached to the dura.
Location	Typically lumbar	May occur anywhere along the spinal axis
Treatment	- Symptoms are most commonly due to tethering of the cord; and are usually improved by untethering. - The bony septum must be removed and the dura reconstituted as a single tube - These spines are often very distorted and rotated, and therefore start at normal anatomy and work towards defect. - ✖ DO NOT cut the tethered filum until after the median septum is removed to avoid having the cord retract up against the septum.	- Consists of untethering the cord at the level of the spina bifida occulta, and occasionally at the level of the split. - More favourable and not necessary need treatment

Type 1 sub types: Mahapatra classification

Subtype	Spur Location	Frequency (%)	Syringomyelia Incidence	Neurological Deterioration Risk	Surgical Complexity	Clinical Outcomes
Type Ia	Center of split - equally duplicated cord above and below spur	50%	7%	0%	Standard	Excellent - no deterioration reported
Type Ib	Superior pole - no space above, large duplicated cord below	17%	80%	0%	Standard	Good - no neurological worsening
Type Ic	Lower pole - large duplicated cord segment above	13%	75%	0%	Standard	Favorable - no postoperative deterioration
Type Id	Straddling bifurcation - extends entire length of split	20%	100%	67%	High Risk	Guarded - highest complication rate

Images

Surgical techniques (Wang 2017)

Indication for Surgery

Type 1 Split Cord Malformation (with an Osseous Divide (SCM-OD))

Tethered Cord Syndrome, which is a primary indication for surgery.

Urination or defecation disorders.
Weakness in both lower extremities.
Talipes equinus (foot deformity).

Asymptomatic patient but has scoliosis that requires orthopaedic surgery.

This is because correcting the scoliosis will stretch the spinal column, and the fixed osseous divide would cause traction and potential injury to the spinal cord.
Most experts believe that if a patient with scoliosis is found to have an SCM-OD, the osseous divide should be surgically removed first, with scoliosis correction following 2–6 months later.

Early surgery is particularly important for children and adolescents in their growth and development period to prevent secondary damage caused by the growth of the spinal cord or daily activities.

Surgical Technique

Preoperative:

Localization

CT-guided positioning is used to accurately locate the osseous divide.
The patient is placed in a prone or lateral position on a CT bed, and a needle is guided to the spinous process, which is then marked with an injection of methylthioninium chloride.

Anaesthesia and Positioning:

The procedure is performed under general anaesthesia with intubation.
The patient is placed in a prone or lateral position on the operating table, positioned so the osseous divide is vertical to the bed to facilitate the operation.

Resection of the Osseous Divide (OD):

Blood vessel on the spur is coagulated
The osseous divide and the spinal canals above and below it are exposed.
The OD is resected using tools such as rongeurs, arc bone chisels, or a high-speed drill.
A wide brain spatula may be used to shield the dura mater and spinal cord from injury, especially when using a grinder.
Care is taken to preserve the integrity of the spinal dura mater during the resection.
Bleeding from the base of the divide, which is vertebral cancellous bone, is managed with bone wax or hemostatic sponge.
Chase spur up to ventral dura where spur may widen beyond vision

Dural Sac Moulding:

After the divide is removed, the dural mater of both spinal cords is cut open to relieve any membrane compression.

Medial roots of the cords are sacrificed

The dura is then sutured to create a single dural cavity containing both semi-spinal cords. The dorsal (back) side is continuously sutured, while the ventral (front) side is intermittently sutured.

Addressing Associated Conditions:

If the patient also has a tethered cord or thickened filum terminale, the filum terminale is cut microscopically to release the tethering.
Other coexisting conditions like syringomyelia or congenital tumours and cysts are also surgically treated at the same time.

Outcomes of Surgery

Overall Surgical Success:

"good results" in a study of 142 patients, with no serious complications such as spinal cord or nerve injury.
Postoperative CT scans confirmed complete resection of the osseous divide in all 142 patients, successfully relieving compression on the spinal cord.

Symptom Improvement:

Partial relief was achieved in patients with symptoms like urination-defecation disorders, muscle strength subsidence, Pes Cavus (high-arched foot), and toe movement disorders.

28 patients experienced relief from preoperative dry stool symptoms
12 patients with poor toe motion had significantly improved fine motor functions.

Neurological Status and Complications:

During a median follow-up of 35 months, no new permanent neurological damage was observed.
Some patients experienced temporary numbness or pain on the surgery side, which typically resolved within 1–2 weeks.
Three patients experienced a temporary decrease in lower limb muscle strength, which fully recovered within three months.

Foundation for Future Scoliosis Treatment:

The surgery creates good conditions for subsequent scoliosis correction.
By removing the osseous divide, the surgery clears the way for a later orthopaedic procedure and avoids traction injury to the spinal cord during scoliosis correction.
In the study, 109 patients underwent scoliosis correction 2–6 months after this initial surgery.