Fluid-filled cavity within the spinal cord. Other nomenclature: hydromyelia, syringohydromyelia, spinal cord cyst.
Signs and Symptoms
Dissociated sensory loss - pain and temperature are disrupted whereas light touch, proprioception, and vibratory sensation are often unaffected. Sensory disturbance is almost always asymmetric in a cape-like over the shoulders and back. Pain is frequently felt in the neck and shoulders.
Central Cord Syndrome: Centrally located syrinx, that injures the fibers located centrally (cervical) before the fibers located laterally (thoracic, lumbar, and sacral, in this order) in the spinal cord. A cervical syrinx often results in early symptoms (sensory loss and motor weakness) of the more distal muscles of the fingers and hands followed by late signs in the proximal muscles of the shoulders, trunk, and later the legs. A thoracic syrinx may cause motor weakness and sensory disturbance of the trunks followed by the legs.
Brainstem symptoms and signs: When the syrinx extends into the brainstem (syringobulbia), symptoms are common early on in the process. These usually consist of dysfunction of the lower cranial nerves with coughing, aspiration, and dysphagia. Scoliosis: May result from unequal weakness of the spinal muscles. Young age, atypical curve, rapid curve progression, and back pain associated with scoliosis should alert one to the possible role of syringomyelia.9
Chronic pain: is associated with a variety of chronic pain syndromes, particularly in posttraumatic syringomyelia, in which there is an initial traumatic injury followed by later spinal cord injury secondary to syrinx distention; however, while it is nearly impossible to determine if the pain is caused by the syrinx or the primary pathology, it appears that treatment of the syrinx rarely results in resolution of the pain, which suggests that the pain may be related to the initial spinal cord injury.
Spinal MRI shows a dilated cavity with the same intensity of CSF on T2-weighted imaging. A complete brain and spinal MRI with and without Gadolinium is needed to determine the primary pathology. Cine MRI may also help in diagnosing abnormal CSF flow patterns. So far, results have been conflicting. Rarely, myelography may help to sort some of the more difficult cases.
Treatment - Based on Etiology
Asymptomatic patients with small syrinx cavities and no obvious etiology are best managed with watchful waiting and serial imaging exams. The management of symptomatic or large syringomyelia is focused on identifying and treating the associated condition, which is the underlying cause of the syrinx.1-4 These etiologies include: Chiari I malformation; congenital tethered cord (spina bifida occulta); acquired tethered cord from previous surgery (such as myelomeningocele repair); spinal arachnoiditis (old viral or bacterial meningitis, etc.); spinal trauma; spinal cord tumor; VP shunt malfunction or Chiari II in spina bifida; idiopathic (unknown cause).
Chiari I malformation: Diagnosis made on MRI. Syrinx associated with Chiari I malformation is usually treated with posterior fossa decompression. If the syrinx does not resolve, one would consider (re-explore the posterior fossa and expand the decompression; consideration of subtle craniocervical instability; consideration of benign intracranial hypertension; consideration of shunting the syrinx directly; others).
Spina bifida: The syrinx may be the result of tethered spinal cord from the myelomenigocele repair, the Chiari II malformation, or ventricular shunt malfunction. The location of the syrinx within the spinal cord may help to dictate the treatment (i.e. lumbar syrinx may respond to tethered cord release and cervical syrinx to VP shunt revision or Chiari II decompression). Most surgeons agree to check the shunt first!
Spina bifida occulta (tethered cord): Diagnosis made on MRI. Patients with congenital tethered spinal cord should undergo exploration and tethered cord release in order to prevent future neurological and urological deficits. If the syrinx is large in cross-sectional diameter, it is often drained at the same surgery.6
Arachnoiditis (spinal inflammation): Diagnosis made on MRI. Spinal cord decompression with dissection of the arachnoid scar is performed. Reestablish normal CSF flow. If the arachnoiditis is so diffuse that it becomes impossible to achieve a good dissection, shunt the syrinx to the pleural or peritoneal cavities.
Spinal trauma: Post-traumatic syrinx is difficult to treat successfully. The syrinx can be a result of arachnoiditis and blockage of flow causing expansion of the cord or may represent an atrophic change secondary to the long-term consequence of a cord contusion.10,12 If a true syrinx is suspected, the treatment would consist of either arachnoidal dissection as above, or a syrinx shunt into the pleura or peritoneum.
Spinal cord tumor: Diagnosis made on MRI. Syringomyelia associated with an intrinsic spinal cord tumor often have 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.11 It is rare to have to shunt the syrinx in these situations.
Idiopathic (unknown cause): In a large percentage of patients, the syrinx has no identifiable cause. Those are difficult to treat. Most large and/or symptomatic syrinxes are treated with syrinx shunting. Rarely, a posterior fossa decompression is found to be successful in the absence of a Chiari malformation. Such patients who respond to decompression are thought to have a Chiari zero. It is so far impossible to predict which patient with idiopathic syringomyelia would respond to posterior fossa decompression. The strict definition of Chiari zero5 is "idiopathic syringomyelia that responds to posterior fossa decompression."
Residual central canal: Many patients are referred for evaluation of a thin, fluid-filled structure within the spinal cord with no associated pathologies. This structure usually tapers at each end and likely represents a normal variant: a remnant of a central canal normally present in embryos. These are usually incidental findings on scans obtained for unrelated issues. The patients are usually neurologically normal. In patients with back pain, other causes of the pain should be investigated.
Prognosis and Outcomes
It is generally accepted that if the causative pathology is identified and treated, the long-term improvement and resolution of the syrinx is good.13 Prognosis is also largely dependent on the prognosis of the primary pathologic that resulted in the syrinx. The syrinx in Chiari I patients generally responds well over time to posterior fossa decompression. In spina bifida, the symptoms must be separated into those related to the syrinx, the tethered cord, shunt malfunction, or less commonly, the Chiari II malformation. The results are often good when the etiology is found8 In spina bifida occulta, a large syrinx has best prognosis with drainage of the syrinx at the time of tethered cord release. A small cavity is likely to remain stable over time and may even regress obviating the need for any treatment other than tethered cord release.6 The diagnosis of tethered spinal cord is made by MRI. In patients with spinal inflammation or arachnoiditis, stabilization of the syrinx can be achieved with decompression and arachnoid dissection in 83% of patients with focal scarring but only 17% of patients with scarring over multiple levels.7 Syrinx shunting alone results in very high recurrence rates. In post-traumatic patients, outcome is largely dependent on the pathology. If pain is secondary to atrophy from chronic damage to the spinal cord, it is not surprising that it will not resolve with shunting of the cavity. Long-term recurrence rates with shunting alone have been in excess of 80%.7 When considering surgical treatment, it should be noted that patients who have undergone previous surgery and failed, may have even worse outcomes. Patients with tumor related syringomyelia generally have good outcomes with tumor resection, assuming the tumor itself is curable. It appears that preoperative neurologic status is the main factor determining neurological outcome.11
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