Q. What is a split cord malformation?

A split cord malformation is a congenital spinal dysraphism in which the spinal cord is longitudinally divided into two hemicords, each containing its own dorsal and ventral nerve roots and central canal. The split is produced by a persistent abnormal midline tract composed of mesenchymal, endodermal, or ectodermal tissue, which physically divides the neural tube. SCM is strongly associated with tethered cord syndrome and progressive neurological deterioration.

 

Q. How are split cord malformations classified?
 

SCM is divided into two main types:

Type I SCM:
The hemicords lie in separate dural sacs, separated by a rigid osseocartilaginous septum. The septum is typically anchored to the vertebral body and creates fixed tethering.
 

Type II SCM:
Both hemicords lie in a single dural sac, separated by a non-rigid fibrous septum. The tethering effect is generally less severe than in Type I.
 

Type I tends to cause earlier and more significant symptoms because the bony spur acts as a fixed mechanical tether.

 

Q. What is the embryological basis of split cord malformations?
 

SCM arises from formation of an accessory neurenteric canal early in development. This abnormal tract allows ectoderm, mesoderm, and endoderm to mix. Mesenchyme condenses along this tract, forming a persistent midline structure that differentiates into either bone/cartilage (Type I) or fibrous tissue (Type II). If the abnormal tract splits the forming dura early, two dural sacs develop; if late or incomplete, a single sac remains.

 

Q. Why is scoliosis common in SCM?
 

Scoliosis develops due to chronic asymmetrical tethering forces acting on the hemicords. The distorted pull on the neuroaxis during growth produces progressive curve formation. Scoliosis may be the presenting feature and should always prompt MRI evaluation for SCM.

 

Q. What are the indications for surgery in SCM?
 

Surgery is indicated for:

Progressive neurological deficits

Orthopedic deformity progression (scoliosis, foot deformity)

Urological deterioration

Presence of a rigid midline septum producing fixed tethering

Associated lesions with high risk, such as dermal sinus tract

Symptomatic tethered cord regardless of type

Type I SCM is generally treated earlier because the rigid septum always produces tethering.

 

Q. What is diastematomyelia?
 

Diastematomyelia is the classical form of Type I Split Cord Malformation, in which the spinal cord is divided into two hemicords by a rigid osseous or cartilaginous septum. The two hemicords lie in separate dural tubes. The septum is usually anchored to the vertebral body, producing a fixed tethering effect.

 

Q. What is the embryological mechanism behind diastematomyelia?
 

It results from early formation of an accessory neurenteric canal, allowing mesenchymal tissue to migrate into the midline and form an osseocartilaginous spur. Because this occurs early in dural development, the dura splits into two separate sacs.

 

Q. What clinical features suggest diastematomyelia?
 

Children usually present with:

Progressive scoliosis

Neurological deterioration: weakness, gait abnormalities

Sensory deficits

Foot deformities (cavovarus, clubfoot)

Orthopedic asymmetry (limb-length difference)

Urological dysfunction

Skin findings such as hairy patches, dermal sinuses, lipomas, dimples, or angiomas frequently overly the defect.

 

Q. What imaging features characterize diastematomyelia?
 

MRI shows two hemicords in separate dural sacs with a midline septum. CT is essential for defining the bony spur. Often associated with vertebral anomalies including hemivertebra or block vertebra.

 

Q. What complications are seen in diastematomyelia surgery?
 

Risks include neural injury, root damage, CSF leak, pseudomeningocele, infection, residual septum causing retethering, and postoperative deformity progression.

 

Q. What is the prognosis for diastematomyelia?
 

Early surgery before severe neurological decline provides the best outcomes. Type I SCMs have a higher retethering risk due to the rigid spur and separate dural sacs.

 

Q. What is diplomyelia?
 

Diplomyelia is a true duplication of the spinal cord, where two complete spinal cords exist side-by-side, each surrounded by its own pia and typically enclosed in a single dural sac. Unlike diastematomyelia, there is no bony or fibrous septum splitting the canal.

 

Q. How is diplomyelia different from diastematomyelia?

 

Diplomyelia: true duplication of the spinal cord, two cords develop independently, usually in a single dural sac, no septum.
 

Diastematomyelia: one cord split into two hemicords by a septum with two dural sacs (Type I SCM).
Diplomyelia is extremely rare compared to diastematomyelia.
 

Q. What is the embryological basis of diplomyelia?
 

It likely results from complete duplication of the notochord or neural plate during early gastrulation, unlike SCM Type I which stems from an accessory neurenteric canal and septum formation.

 

Q. How does diplomyelia present clinically?
 

Symptoms resemble tethered cord: gait disturbance, weakness, sensory changes, scoliosis, orthopedic deformities, and bladder dysfunction. Skin markers may be present but are less consistent than in diastematomyelia.

 

Q. What does MRI show in diplomyelia?
 

MRI shows two fully formed cords without a septum and usually within one dural sac. No bony spur is seen. Associated anomalies may include tethered cord, dermoid, lipoma, or segmentation abnormalities.

 

Q. How is diplomyelia treated?
 

Surgery aims to de-tether the cord, release any adhesions, and perform duraplasty. Because there is no bony spur to remove, surgery focuses on freeing the cords from tethering bands and reconstructing a capacious dural sac. Care must be taken not to confuse duplicated cords with roots or placode.

 

Q. What is the prognosis of diplomyelia?
 

Generally depends on associated anomalies and extent of tethering. Outcomes are better than in diastematomyelia because no rigid septum is present. Long-term follow-up is essential due to risk of retethering.

 

Surgical Steps for Split Cord Malformation: 

 

I will position the child prone with careful padding of all pressure points and mark the midline over the suspected split cord level. After a wide antiseptic preparation and draping, I will make a midline incision and expose the posterior elements of the spine. I will perform a laminectomy or laminotomy spanning the entire cranio-caudal extent of the split so that both the septum and both hemicords are fully accessible. I will remove only the minimum bone needed to avoid postoperative instability while still ensuring complete visualization of the midline spur and the dural sleeves.

 

Under the operating microscope, I will open the dura longitudinally. In Type I split cord malformation, I will encounter two separate dural sacs, each containing a hemicord. I will open each dural tube along its length and tack the margins laterally to maintain exposure. I will then identify the rigid osseous or cartilaginous septum that divides the canal. This septum is often attached deeply to the posterior vertebral body, so I will carefully dissect around it circumferentially to define its margins. Using a high-speed drill, fine osteotomes, or micro-rongeurs, I will remove the septum completely from dorsal to ventral, ensuring that the entire bony anchor at its base is eliminated. I will work slowly and precisely to avoid injury to the hemicords and their exiting roots, which may course very close to the septum.

 

In Type II split cord malformation, I will find both hemicords within a single dural sac, separated by a fibrous band. In this situation, I will sharply dissect the fibrous septum away from the neural tissue, cutting it completely to release the abnormal tethering connection. I will also look for additional tethering structures such as arachnoidal adhesions, fibrofatty bands, or thickened filum components, and I will divide these carefully to ensure the hemicords are entirely free.

 

After removing the septum in Type I or releasing the fibrous band in Type II, I will inspect the conus and both hemicords to ensure they move freely without fixed points. I will then create a single, capacious dural sac for both hemicords. In Type I, this requires unifying the two dural sleeves by incising their medial walls and reconstructing one large dural space. I will perform a generous duraplasty using autologous fascia or a synthetic graft to prevent postoperative retethering and to allow the neural elements enough room for physiological movement. I will close the dura in a watertight fashion with fine sutures, ensuring no leaks or tension points remain.

 

Once the dura is closed, I will close muscle, fascia, subcutaneous tissue, and skin in layered fashion, taking care to avoid tension that might compromise wound healing. I will maintain meticulous hemostasis and confirm that the reconstructed canal has no compressive elements remaining. Postoperatively, I will monitor neurological function, bladder status, and wound integrity, and arrange follow-up imaging to assess the adequacy of detethering and exclude retethering or postoperative complications.