Syringomyelia is the development of a fluid-filled cavity or syrinx within the spinal cord. Hydromyelia is a dilatation of the central canal by cerebrospinal fluid (CSF) and may be included within the definition of syringomyelia. Types of syringomyelia include the following:
1)Syringomyelia with fourth ventricle communication
About 10% of syringomyelia cases are of this type. This communication can be observed on MRI. In some cases, a blockage of CSF circulation occurs. A shunt operation may be the best therapeutic option for these patients.
2)Syringomyelia due to blockage of CSF circulation (without fourth ventricular communication)
Representing at least 50% of all cases, this is the most common type of syringomyelia. Obstruction of CSF circulation from the basal posterior fossa to the caudal space may cause syringomyelia of this type. The most common example is Arnold-Chiari malformation, which also is associated with communicating syringomyelia. Other causes include the following:
Basal arachnoiditis (postinfectious, inflammatory, postirradiation, blood in subarachnoid space)
Basilar impression or invagination
Meningeal carcinomatosis
Pathological masses (arachnoid cysts, rheumatoid arthritis pannus, occipital encephalocele, tumors)
3)Syringomyelia due to spinal cord injury
Fewer than 10% of syringomyelia cases are of this type. Mechanisms of injury include (1) spinal trauma, (2) radiation necrosis, (3) hemorrhage from aneurysm rupture or arteriovenous malformation or in a tumor bed, (4) infection (spinal abscess, human immunodeficiency virus, transverse myelitis), and (5) cavitation following ischemic injury or degenerative disease.
4)Syringomyelia and spinal dysraphism
Spinal dysraphism may cause syringomyelia through a variety of mechanisms, including those mentioned under the previous 3 categories. Identification and treatment of associated dysraphism has the greatest impact on arresting progression of syringomyelia.
5)Syringomyelia due to intramedullary tumors
Fluid accumulation usually is caused by secretion from neoplastic cells or hemorrhage. The tumors most often associated with syringomyelia are ependymoma and hemangioblastoma. Extramedullary intradural and extradural tumors are considered separately under the second category because the mechanism of syrinx formation is blockage of the CSF pathway.
6)Idiopathic syringomyelia
Idiopathic syringomyelia has an unknown cause and cannot be classified under any of the previous categories.
Medical Care:
No medical treatment is known for patients with syringomyelia. However, a chronic, stable clinical course is common. Identifying the underlying cause of syrinx formation is very important. Surgical treatment most likely will be necessary.
Neurorehabilitative care facilitates preservation of remaining neurological functions and prevents complications of quadriparesis such as infection and decubitus ulcers.
Surgical Care: A variety of surgical treatments have been proposed for syringomyelia.
Suboccipital and cervical decompression
This operation includes suboccipital craniectomy; laminectomy of C1, C2, and sometimes C3; and duraplasty.
Some authors report microsurgical lysis of any adhesions, opening of the fourth ventricular outlet, and plugging of the obex (later steps are based on Gardner▓s hydrodynamic theory).
Laminectomy and syringotomy (dorsolateral myelotomy)
After decompression, the syrinx is drained into the subarachnoid space through a longitudinal incision in the dorsal root entry zone (between the lateral and posterior columns), usually at the level of C2-C3.
Incision in the dorsal root entry area has the minimum risk of increasing neurological deficit.
Shunts
Ventriculoperitoneal shunt - Indicated if ventriculomegaly and increased intracranial pressure are present
Lumboperitoneal shunt - Placed infrequently because of increased risk of herniation through the foramen magnum
Syringosubarachnoid dorsal root entry zone shunt
Syringoperitoneal shunt
Fourth ventriculostomy
Percutaneous needling: This technique is advocated as a possible mode of therapy; however, rapid refilling of the hydromyelic cavity from the ventricular system follows aspiration of fluid at the time of surgery. Moreover, a needle track seems unlikely to remain open.
Terminal ventriculostomy
The terminal ventricle is the dilated portion of the central canal that extends below the tip of the conus medullaris into the filum terminale. A laminectomy is performed over the caudal limit of the fluid sac, and the filum is opened.
This procedure is suitable only in patients with symptoms of syrinx without Chiari malformation. It is inappropriate in cases in which the hydromyelic cavity does not extend into the lumbar portion of the spinal cord or into the filum terminale.
Neuroendoscopic surgery
A fibroscope inserted through a small myelotomy allows inspection of the intramedullary cavity.
This technique is particularly useful in evaluating and treating multiple septate syrinxes.
Septa are fenestrated, either mechanically or by laser. Fluid from the cavity is then shunted into the subarachnoid space.
