The Operation for Syringomyelia in Children

The management of syringomyelia is focused on identifying and treating the associated condition that is the underlying cause of the syrinx (2-4, 9). These etiologies include Chiari I malformation, congenital tethered cord (spina bifida occulta), acquired tethered cord from previous surgery (such as myelomeningocele repair), spinal arachnoiditis, spinal trauma, spinal cord tumor, ventriculoperitoneal shunt malfunction or Chiari II malformation in spina bifida, and idiopathic (17).

• Small syrinxes and Chiari 0: Small idiopathic syrinxes are usually asymptomatic and can be followed conservatively. If the syrinx is progressive and a thorough investigation fails to reveal an etiology, several options for treatment can be considered, one of which includes direct shunting of the syrinx. However, the treatment of idiopathic syringomyelia may not be limited to syrinx shunting. The Chiari 0 malformation, i.e., patients with idiopathic syringomyelia who respond to posterior fossa decompression (in the absence of tonsillar herniation on MRI), is such an example. Although it is becoming well established that this entity exists, there are no preoperative diagnostic techniques that help to distinguish between Chiari 0 and true idiopathic syringomyelia.
• Chiari I malformation: Syrinx associated with Chiari I malformation is usually treated with posterior fossa decompression. If the syrinx does not resolve, many experienced surgeons will consider re-exploring the posterior fossa and expanding the decompression before considering shunting the syrinx.
• Spina bifida aperta: In spina bifida aperta, the syrinx may be the result of tethered spinal cord from the myelomeningocele repair, the Chiari II malformation, or ventricular shunt malfunction. The location of the syrinx in the spinal cord may help to dictate the treatment (i.e., lumbar syrinx may respond to tethered cord release and cervical syrinx to ventriculoperitoneal shunt revision or Chiari II decompression) (17). It has become clearer in the past few years that a shunt revision will, in most cases, eliminate the need for decompressing a Chiari II malformation even when the ventricles have not dilated due to the shunt’s malfunction. Thus, decompressing the Chiari II malformation has become a very rare occurrence in most pediatric centers. Nonetheless, addressing the shunt first is always a safe start.
• Spina bifida occulta: Patients with congenital tethered spinal cord should undergo exploration and tethered cord release to prevent future neurological and urological deficits. If the syrinx is large in cross-sectional diameter, it is often drained at the same surgery (11).
• Arachnoiditis: In patients with arachnoiditis from trauma, meningitis, or other inflammatory problems, spinal cord decompression with dissection of the arachnoid scar is performed. All attempts should be made to reestablish normal CSF flow. When the arachnoiditis is so diffuse that it becomes impossible to achieve a good dissection, shunting the syrinx to the pleural or peritoneal cavities becomes important.
• Spinal trauma: The most difficult patients to treat are those with posttraumatic syringomyelia. In these patients, the syrinx can be a result of arachnoiditis and blockage of flow, causing expansion of the cord. Alternatively, the syrinx may represent ex-vaccuo change secondary to the long-term consequence of a cord contusion– atrophy (33, 37). If a true syrinx is suspected, the treatment would consist of either arachnoidal dissection, as stated above, or a syrinx shunt into the pleura or peritoneum, as noted above.
• Spinal cord tumor: Syringomyelia associated with an intrinsic spinal cord tumor often has high protein content and may represent a secretory process from the tumor cells or an obstructive process similar to other etiologies. Patients with tumor-related cysts should be treated with tumor resection (34). It is rare to have to shunt the syrinx in these situations.

Patient Positioning

• Patient positioned prone or lateral: The prone position is used for syringosubarachnoid shunts and the lateral position for syringopleural and syringoperitoneal shunts.
• No head holder

Surgical Approach

• Skin incision: A straight vertical incision is made in the midline.
• Laminectomy/laminotomy: A full laminectomy is performed for the desired level of access to the cyst.
• Dural opening: The dura is opened in the midline, and dural tack-up sutures are placed. A surgical microscope is brought to field. When needed, the subarachnoid space is developed with microsurgical dissection.

Intervention

• Syrinx exposure: In choosing the location of the myelotomy, two priorities exist: 1) to open the spinal cord as low as possible to minimize the potential for postoperative neurological deficits, and 2) to ensure that the cord at the entry site is as thin as possible. Surgical judgment is required to find a compromise between these two priorities. Preoperative MRI, as well as intradural or extradural ultrasonography, can be used to assist in this decision.
• Myelotomy: Once the spinal level is chosen and part of the syrinx to be entered is exposed, a decision is made on the exact location of the myelotomy. The spinal cord can be opened between the dorsal columns, at the dorsal root entry zone, or, alternatively, at any location where the cord seems thinnest because of the cystic dilatation. If the decision is made to enter the cord between the dorsal columns, but the columns cannot be easily identified because of distortion from the cyst, then eliciting SSEPs directly from the dorsal columns can be easily achieved. The cord can be entered in the silent zone between the two dorsal columns.
• Proximal shunt catheter placement: Once the location of the myelotomy is determined, it is achieved with an 11-blade scalpel or a microsurgical dissector. A straight or T-tube catheter is brought to the field. The two ends of the T are trimmed and placed in the syrinx cavity superiorly and inferiorly, and the tail of the T is placed in the subarachnoid space. The tube is anchored to the adjacent pia and/or dura with a small (7-0) prolene suture.
• Distal shunt catheter placement: The distal end of syrinx shunts can be placed in the subarachnoid space, peritoneum, or pleural cavity. A syringosubarachnoid shunt is the preferred treatment option. When there is significant arachnoiditis, the tube can be tunneled toward the pleural or peritoneal cavity. For ease of tunneling, cervical to mid-thoracic tubes are usually placed in the pleural cavity and low thoracic and lumbar tubes in the peritoneum. The tunneling is identical to ventriculoperitoneal shunt procedures. Low-pressure valves are routinely used to prevent collapse of the syrinx, and valves with reservoirs may be of benefit to allow access for CSF sampling and pressure measurements.

Closure

• Routine dural closure: Routine dural watertight closure is done, usually with 6-0 PDS suture; occasionally, a dural graft will be required.
• Routine muscle and fascial closure
• Routine skin closure