eMedicine Specialties > Radiology > Brain/Spine

Syringohydromyelia

Author: Farhood Saremi, MD, Professor of Radiology, Director of Cardiothoracic Radiology, Department of Radiological Sciences, University of California-Irvine
Coauthor(s): Chi-Shing Zee, MD, Chief of Neuroradiology, Professor, Departments of Radiology and Neurosurgery, University of Southern California School of Medicine; John L Go, MD, Assistant Professor, Department of Radiology, Section of Neuroradiology, Keck School of Medicine, University of Southern California Medical Center
Contributor Information and Disclosures

Updated: Dec 10, 2008

Introduction

Background

Tubular cavitation of the spinal cord, along with associated progressive neurologic symptoms, has long attracted medical interest. An accumulation of cerebrospinal fluid (CSF) may lead to simple distention of the central canal of the spinal cord; in such cases, the cavity is lined by ependymal cells (ie, hydromyelia). Alternatively, an accumulation of CSF may dissect into the surrounding white matter to form a paracentral cavity, in which case none of the cavity is lined by ependyma (ie, syringomyelia). In many, if not most, cases, both hydromyelia and syringomyelia are present (ie, syringohydromyelia). As the syringomyelic cavity expands, the initial hydromyelic cavity compresses, and the communication between the 2 cavities may atrophy and be lost. Hydromyelia and syringomyelia may be difficult to distinguish even after a detailed histologic examination.^1,2,3,4

In 1973, Barnett et al published a classic article on the etiology of syringomyelia.⁵ The authors classified syringohydromyelic cavities into 5 types:

1. Communicating (with the subarachnoid space, usually at the level of the obex at the inferior aspect of the fourth ventricle)
2. Posttraumatic
3. Tumor-related
4. Arachnoiditis-related
5. Idiopathic

In a study by Milhorat et al, the intramedullary cavities were classified into communicating, noncommunicating, and atrophic types to conform to the classification of the ventricular enlargements of the brain.⁶

Overall, the etiologies of communicating hydrocephalus include subarachnoid hemorrhage, meningitis, neoplastic seeding of the leptomeninges, and idiopathic causes. A model of the communicating type may be produced by injecting sclerosing agents into the cisterna magna. Obstruction of the basilar subarachnoid cisterns results in symmetric enlargement of the CSF cavities proximal to the blockage, including all 4 cerebral ventricles and the central canal of the spinal cord.^7,8,9

Noncommunicating syringes are subdivided into 6 types:

1. Chiari II malformation with hydrocephalus
2. Chiari I malformation without hydrocephalus
3. Extramedullary compressive lesions at the craniocervical junction or along the length of the spinal canal
4. Spinal cord trauma
5. Intramedullary tumors and intraperimedullary infections
6. Multiple sclerosis

Adhesive spinal arachnoiditis may develop postoperatively or after trauma; following pyogenic, tuberculous, or luetic (syphilitic) meningitis; or after bleeding into the subarachnoid space. Atrophic syringes, which occur with myelomalacia (following trauma or infarction), are associated with a reduction in the transverse dimensions of the spinal cord. Atrophic syringes are limited to a discrete area of myelomalacia in a manner similar to the porencephalic cysts that occur in some cases of encephalomalacia.

Other associated findings include Klippel-Feil anomaly, basilar impression, scoliosis, craniovertebral fusion, and hydrocephalus.

Presentation

Demographics

• Males and females are equally affected.
• Syringomyelia is usually encountered in adults but occasionally occurs in infants. The youngest reported infant was 5 weeks of age.
• A direct communication between the syrinx cavity and the fourth ventricle via the obex is present in 14% of patients. Distended syringes that do not communicate with the fourth ventricle are present in 65% of patients. The syrinx-free segment between the syrinx and the obex of the fourth ventricle, as reported, has varied in length from a few centimeters to more than 50 cm.
• The Chiari I malformation is a congenital disorder defined by the caudal displacement of the cerebellar tonsils through the foramen magnum and into the cervical spinal canal. Cerebellar tonsillar ectopia is usually considered to be present when the lower border of the tonsils are more than 5 mm below the plane of the foramen magnum, although the remodeling of the inferior margins of the tonsils into a wedge shape is a more reliable observation. The presence of a small or narrowed posterior fossa may also be useful. The incidence of syringomyelia of any degree with Chiari I malformation has been reported to be 20-70%. Holocord hydromyelic cavities are seen in 30% of patients with Chiari I malformation and associated syringomyelia.¹⁰
• The incidence of syringomyelia associated with an intramedullary neoplasm has been reported to be 25-58%. Ependymomas and hemangioblastomas are the most common tumor types to be associated with syringes. Astrocytomas tend to demonstrate syringes less often. In patients with von Hippel—Lindau disease and von Recklinghausen disease, there appears to be a predilection for cyst development within the associated neoplasm.
• In cases of spinal trauma, the incidence of syringomyelia above the spinal fracture site is approximately 3-5%. With the longer survival times currently observed in paraplegic and quadriplegic patients, the incidence of posttraumatic syringomyelia is likely to increase in the future.

Williams wrote that obstructions at the level of the foramen magnum produce a dissociation of pressure between the cranial and spinal CSF compartments.¹² Fluid is "sucked" from the fourth ventricle into the central canal as a consequence of a relatively lower pressure caudal to the blockage. Other authors, while agreeing that a pressure gradient contributes to syrinx formation, have proposed that the CSF enters the central canal from the spinal subarachnoid space through the enlarged Virchow-Robin spaces as a consequence of increased intraspinal pressure. Hydrodynamic theories have been broadly applied to other types of syrinx formation. Valsalva maneuvers, such as sneezing, coughing, and straining, presumably accentuate the phenomenon by producing sudden changes in spinal venous volume and pressure.

The progression of syringomyelia associated with Chiari I malformation has also been attributed to the pulsatile action of the cerebellar tonsils¹³ ; however, the significance of this finding remains unclear, and this does not necessarily correlate with the presence or absence of symptoms. According to a theoretical model of pressure wave propagation in fluid-filled elastic tubes, the increased pulse pressure that may occur in a region of stenosis of the spinal subarachnoid space (an elastic jump) may be another contributory mechanism for the generation of syringes.

Studies using magnetic resonance imaging (MRI) flow techniques have shown that abnormal global intracranial compliance may play an important role in the generation of syringomyelia and may be a useful parameter in estimating the outcome of decompression surgery in patients with Chiari I malformations.

Basal arachnoiditis (chronic meningitis, subarachnoid hemorrhage, idiopathic origin) may be associated with communicating hydrocephalus. The restriction of CSF equilibration has been proposed as the responsible factor.

Extramedullary lesions, such as chronically herniated discs, basilar impression, and intradural masses, may be associated with syringohydromyelia. In most patients, syringes are found at the lower border of the compressed segment of the spinal cord and are separated from the fourth ventricle by a syrinx-free segment. The location of syringes immediately below an extramedullary obstruction raises the possibility that extrinsic compression of the central canal contributes to dilatation of the lumen caudal to the blockage; however, because syringes are occasionally encountered at or above the level of the extramedullary tumors, the precise mechanism of syrinx formation in these cases is unclear.

A distinctive feature of posttraumatic syringes is their tendency to extend rostrally from the level of the injury. Unless there are associated disturbances in the CSF dynamics caused by conditions such as arachnoid scarring or cord tethering, posttraumatic syringes may not be explained by conventional theories. With intramedullary tumors and infections, the most common cause of spinal cord cavitation is cystic degeneration of the primary neoplastic or infectious lesion. The necrotic process tends to begin centrally and can extend rostrally, caudally, or both ways. Factors independent of the tumor (in particular, disturbances of CSF and extracellular fluid flow) are postulated to play major roles in the pathogenesis of syrinx formation associated with intramedullary tumors. The same factors may apply in cases of intramedullary infection.^14,15

Mechanisms that have been proposed to account for cases of adhesive spinal arachnoiditis include vascular compromise, CSF blockage, and fixation of the spinal cord from meningeal scarring. Focal scarring and spinal blockage may obstruct spinal CSF circulation and force CSF into the spinal cord via perivascular spaces. Circumferential fixation of the spinal cord may create an intrinsic negative pressure within the spinal cord, a process that may further promote the accumulation of fluid in the cord.^16,17,18

Pain and neurologic complaints may be exacerbated by coughing and sneezing. Progressive scoliosis may be encountered and tends to be localized to the upper thoracic spine. Brainstem findings, including nystagmus, dysphagia, and lower nerve palsies, are present in a small number of patients. Neurogenic arthropathy (ie, Charcot joints) is an unusual event; it occurs in fewer than 5% of patients with syringomyelia.

Posttraumatic syringomyelia may develop after either severe or relatively minor spinal cord injury. Enlarging posttraumatic syringomyelia is manifested clinically by a progressive neurologic deficit that extends some distance above the initial site of injury. The clinical problem may develop from several months to many years after the initial injury.

Treatment

Because syringomyelia is a complex pathologic disorder, its treatment is multifaceted and includes a variety of surgical options. Effective syrinx decompression has the potential to reverse neurologic deficits caused by increased intramedullary pressure, but it does not affect deficits caused by the pathologic abnormalities of spinal cord cavitation.^19,20,21,22

Traditional surgical approaches are based on prevailing concepts of syringomyelia pathogenesis. Treatment of communicating syringomyelia and syringes associated with Chiari II malformation with hydrocephalus consists of placement of a ventriculoperitoneal shunt. Decompressive surgery, including limited suboccipital craniectomy and C1 laminectomy with duraplasty, is generally considered the procedure of choice in syringes associated with Chiari I malformations. A significant improvement is observed in 50% of patients.

An adjunct surgical approach to the treatment of Chiari I malformation is syrinx shunting. Shunts to the spinal subarachnoid space are less reliable than shunts to the cerebellopontine angle cistern or to the peritoneal cavity. Other forms of treatment remain controversial; these include shunting of the fourth ventricle, plugging of the obex, and excision of the cerebellar tonsils. Patients who come to surgical attention late in the disease course and who undergo a rapid loss of neurologic function tend to do poorly. Because the time course of the neurologic change is typically long, a follow-up period of less than 5-10 years after surgery is of questionable value in assessing the final response to therapy.

Initial treatment of syringes occurring with extramedullary lesions should consist of surgical excision of the primary lesion and decompression of the blockage/compression.

Posttraumatic syringes may be treated with the use of syringospinal, syringocisternal, or syringoperitoneal shunts. Posttraumatic cystic myelopathy may occur with or without the presence of the tethered cord syndrome. Detection and removal of the cause of a CSF flow abnormality, such as arachnoid scarring, cord untethering, or both, with duraplasty to expand the subarachnoid space may be, in some cases, a more physiologically sound approach. In general, patients with posttraumatic syringomyelia respond favorably to surgery.

Treatment of atrophic syringomyelia is limited to relieving symptoms related to the causal lesion. Operative findings that are associated with a more unsatisfactory result include the presence of dense basal cistern or spinal canal arachnoiditis .

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