Syringomyelia

Background

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. The following are types of syringomyelia.

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.

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 is also associated with communicating syringomyelia. Other causes include the following:

• Basal arachnoiditis (postinfectious, inflammatory, postirradiation, blood in subarachnoid space)^[1]
• Basilar impression or invagination
• Meningeal carcinomatosis
• Pathological masses (arachnoid cysts, rheumatoid arthritis pannus, occipital encephalocele, tumors)

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.

Syringomyelia and spinal dysraphism

Spinal dysraphism may cause syringomyelia through a variety of mechanisms, including those mentioned under the previous three categories. Identification and treatment of associated dysraphism has the greatest impact on arresting progression of syringomyelia.

Syringomyelia due to intramedullary tumors

Fluid accumulation is usually 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.

Idiopathic syringomyelia

Idiopathic syringomyelia has an unknown cause and cannot be classified under any of the previous categories.^[2] Surgical decompression can help in some patients with remarkable neurologic deficit.

• References

Pathophysiology

Although many mechanisms for syrinx formation have been postulated, the exact pathogenesis is still unknown. Frequently cited theories are those of Gardner, William, and Oldfield.

Gardner's hydrodynamic theory

This theory proposes that syringomyelia results from a "water hammer"-like transmission of pulsatile CSF pressure via a communication between the fourth ventricle and the central canal of the spinal cord through the obex. A blockage of the foramen of Magendie initiates this process.^[3]

William's theory

This theory proposes that syrinx development, particularly in patients with Chiari malformation, follows a differential between intracranial pressure and spinal pressure caused by a valvelike action at the foramen magnum.^[4] The increase in subarachnoid fluid pressure from increased venous pressure during coughing or Valsalva maneuvers is localized to the intracranial compartment.

The hindbrain malformation prevents the increased CSF pressure from dissipating caudally. During Valsalva, a progressive increase in cisterna magna pressure occurs simultaneously with a decrease in spinal subarachnoid pressure. This craniospinal pressure gradient draws CSF caudally into the syrinx.

Oldfield's theory

Downward movement of the cerebellar tonsils during systole can be visualized with dynamic MRI. This oscillation creates a piston effect in the spinal subarachnoid space that acts on the surface of the spinal cord and forces CSF through the perivascular and interstitial spaces into the syrinx raising intramedullary pressure. Signs and symptoms of neurological dysfunction that appear with distension of the syrinx are due to compression of long tracts, neurons, and microcirculation. Symptoms referable to raised intramedullary pressure are potentially reversible by syrinx decompression.^[5]

The intramedullary pulse pressure theory

The here-proposed intramedullary pulse pressure theory instead suggests that syringomyelia is caused by increased pulse pressure in the spinal cord and that the syrinx consists of extracellular fluid. A new principle is introduced implying that the distending force in the production of syringomyelia is a relative increase in pulse pressure in the spinal cord compared to that in the nearby subarachnoid space. The formation of a syrinx then occurs by the accumulation of extracellular fluid in the distended cord.

• References

Etiology

Etiology of syringomyelia often is associated with craniovertebral junction abnormalities.

Bony abnormalities include the following:

• Small posterior fossa
• Platybasia and basilar invagination
• Assimilation of the atlas

Soft-tissue masses of abnormal nature include the following:

• Tumors (eg, meningioma at foramen magnum)
• Inflammatory masses

Neural tissue abnormalities include the following:

• Cerebellar tonsils and vermis herniation
• Chiari malformation

Membranous abnormalities include the following:

• Arachnoid cysts^[11] , rhombic roof, or vascularized membranes
• Posthemorrhagic or postinflammatory membranes

Other etiologies not associated with craniovertebral abnormalities may include the following:

• Arachnoid scarring related to spinal trauma
• Arachnoid scarring related to meningeal inflammation
• Arachnoid scarring related to surgical trauma
• Subarachnoid space stenosis due to spinal neoplasm or vascular malformation
• Subarachnoid space stenosis, with possible scarring, related to disk and osteophytic disease
• Idiopathic

• References

Epidemiology

Estimated prevalence of the disease is about 8.4 cases per 100,000 people and occurs more frequently in men than in women. The disease usually appears in the third or fourth decade of life, with a mean age of onset of 30 years. Rarely, syringomyelia may develop in childhood or late adulthood.

• References

Prognosis

Prognosis depends on the underlying cause, the magnitude of neurological dysfunction, and the location and extension of the syrinx.

Patients presenting with moderate or severe neurological deficits fare much worse than those patients with mild deficits. Patients with central cord syndrome have poor response to treatment.

Natural history of syringomyelia still is not well understood. Although older studies had suggested that 20% of patients died at an average age of 47 years, mortality rates are likely lower in today's patients as a result of surgical interventions and better treatment of complications associated with significant paresis, such as pulmonary embolism.^[15]

• References

Complications

Myelopathy is the most serious consequence of syringomyelia. The following are the seven grade classifications of disability from myelopathy according to the Modified Nurick Classification.

• Grade 0 - No root signs or symptoms
• Grade I - Root signs or symptoms; no evidence of cord involvement
• Grade II - Signs of cord involvement; normal gait
• Grade III - Mild gait abnormality; able to be employed
• Grade IV - Gait abnormality prevents employment
• Grade V - Able to ambulate only with assistance
• Grade VI - Chairbound or bedridden

Complications due to myelopathy include the following:

• Recurrent pneumonia
• Paraplegia or quadriplegia
• Decubitus ulcers
• Bowel and urinary dysfunction

Mortality/morbidity

Assessing treatment results is difficult because of the rarity of syringomyelia, variability of presentation and natural history, and the relatively short follow-up in most studies.

In one study, half of all patients with syringomyelia were in clinically stable condition for several years.

Although an older study had suggested that 20% of patients died at an average of 47 years, mortality rates are likely lower in today's patients as a result of surgical interventions and better treatment of complications associated with significant paresis, such as pulmonary embolism.

• References

History

Syringomyelia usually progresses slowly; the course may extend over many years. The condition may have a more acute course, especially when the brain stem is affected (i.e., syringobulbia). Syringomyelia usually involves the cervical area. Symptomatic presentation depends primarily on the location of the lesion within the neuraxis. Clinical manifestations are discussed in the sections that follow.

Sensory

Syrinx interrupts the decussating spinothalamic fibers that mediate pain and temperature sensibility, resulting in loss of these sensations, while light touch, vibration, and position senses are preserved (dissociated sensory loss).

When the cavity enlarges to involve the posterior columns, position and vibration senses in the feet are lost; astereognosis may be noted in the hands.

Pain and temperature sensation may be impaired in either or both arms, or in a shawllike distribution across the shoulders and upper torso anteriorly and posteriorly.

Dysesthetic pain, a common complaint in syringomyelia, usually involves the neck and shoulders, but may follow a radicular distribution in the arms or trunk. The discomfort, which is sometimes experienced early in the course of the disease, generally is deep and aching and can be severe.

Motor

Syrinx extension into the anterior horns of the spinal cord damages motor neurons (lower motor neuron) and causes diffuse muscle atrophy that begins in the hands and progresses proximally to include the forearms and shoulder girdles. Clawhand may develop.

Respiratory insufficiency, which usually is related to changes in position, may occur.

Autonomic

Impaired bowel and bladder functions usually occur as a late manifestation.

Sexual dysfunction may develop in long-standing cases.

Horner syndrome may appear, reflecting damage to the sympathetic neurons in the intermediolateral cell column.

Extension of the syrinx

A syrinx may extend into the medulla, producing a syringobulbia.^{[6, 7]} This syndrome is characterized by dysphagia, nystagmus, pharyngeal and palatal weakness, asymmetric weakness and atrophy of the tongue, and sensory loss involving primarily pain and temperature senses in the distribution of the trigeminal nerve.

Rarely, the syrinx cavity can extend beyond the medulla in the brain stem into the centrum semiovale (syringocephalus).

Lumbar syringomyelia can occur and is characterized by atrophy of the proximal and distal leg muscles with dissociated sensory loss in the lumbar and sacral dermatomes. Lower limb reflexes are reduced or absent. Impairment of sphincter function is common.

Other manifestations

Painless ulcers of the hands are frequent. Edema and hyperhidrosis can be due to interruption of central autonomic pathways.

Neurogenic arthropathies (Charcot joints) may affect the shoulder, elbow, or wrist.^[8] Scoliosis is seen sometimes.^{[9, 10]}

Acute painful enlargement of the shoulder is associated with destruction of the head of the humerus.

• References

Physical Examination

A complete physical examination may reveal diminished arm reflexes, which are sometimes present early in the clinical course of syringomyelia.

Lower limb spasticity, which may be asymmetrical, appears with other long-tract signs such as paraparesis, hyperreflexia, and extensor plantar responses.

Rectal examination includes an evaluation of volitional sphincter control and sensory assessment of sacral dermatomes.

Dissociated sensory impairment may be noted.

The syrinx may extend into the brain stem, affecting cranial nerves or cerebellar function.

Brainstem signs are common in syringomyelia associated with Chiari malformations.

• References

Imaging Studies

The initial evaluation of patients suspected of having a spinal cord syrinx includes a comprehensive history and physical examination.

Information obtained from examinations guides the imaging studies. Essential tests include plain radiographic series with dynamic views and high-resolution CT scan to assess the bony spinal canal.

The most sensitive imaging test for soft tissue is an MRI scan. Gadolinium-enhanced images are also helpful in differentiating between tumor, scar, and disk material, especially in postoperative or posttraumatic cases.

Magnetic resonance imaging

Physicians primarily use magnetic resonance imaging (MRI) to diagnose syringomyelia.

Imaging of the entire rostrocaudal extension of the cyst or cysts is important. Gadolinium-enhanced images are indicated if a tumor is suspected. Gadolinium-enhanced images are helpful in differentiating between scar or disk material associated with a syrinx, especially in postoperative or posttraumatic cases.

MRI examination should include sagittal and transverse views in T1 and T2 images (see image below). Proton density scans also can be helpful.

View Image

Sagittal T1-weighted image showing a thoracic syrinx.

Magnetic resonance angiography can be especially helpful in cases of syringomyelia associated with vascular lesions.

Cine phase-contrast MRI is used to analyze CSF flow dynamics near the spinal cord cyst.

Myelography

Myelography is performed in special situations when MRI cannot be used. Widening of the cord and complete subarachnoid block may be observed.

Myelogram combined with immediate and delayed high-resolution CT scan also can be performed. Delayed CT scans are obtained 4-24 hours after the initial testing and can demonstrate cyst filling.

• References

Other Tests

In neurophysiological assessment by somatosensory evoked potentials (SSEPs), low-amplitude or delayed responses are present in myelopathy.

Neurophysiological assessment by motor evoked response may be more sensitive than SSEPs in the evaluation of spinal cord dysfunction.

• References

Histologic Findings

The syringomyelic cavity, or syrinx, forms most commonly in the lower cervical region, particularly at the base of the posterior horn and extending into the central gray matter and anterior commissure of the cord.

Histopathologic findings include (1) cavitation of spinal cord gray matter, (2) syrinx continuous with or adjacent to the central canal, and (3) an inner layer of gliotic tissue.

In association with the syrinx, other pathological conditions such as tumors, vascular anomalies, or infective processes also may be evident.

• References

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.

• References

Surgical Care

A variety of surgical treatments have been proposed for syringomyelia and are discussed in the sections that follow.

Suboccipital and cervical decompression

This operation includes suboccipital craniectomy; laminectomy of C1, C2, and sometimes C3; and duraplasty.^{[12, 13]}

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

The following types of shunts may be indicated:

• 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

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

This technique is particularly useful in evaluating and treating multiple septate syrinxes.

A fibroscope inserted through a small myelotomy allows inspection of the intramedullary cavity. Septa are fenestrated, either mechanically or by laser. Fluid from the cavity is then shunted into the subarachnoid space.

Surgical untethering in select cases with posttraumatic tethering associated with syringomyelia^[14]

• References

Medication Summary

No specific medication is indicated for treatment of syringomyelia. However, analgesics and muscle relaxants may be given for symptomatic treatment.

• References

Ibuprofen (Ibuprin, Advil, Motrin)

• Dosing, Interactions, etc.

Clinical Context:  One of propionic acid derivatives group. Effective inhibitor of cyclooxygenase, which is responsible for biosynthesis of prostaglandins; rapidly absorbed after PO administration; half-life in plasma is about 2 h; passes slowly into synovial spaces and may remain there in higher concentration as concentrations in plasma decline; excretion is rapid and complete, mainly in urine as metabolites or their conjugates.

• References

Aspirin (Anacin, Ascriptin, Bayer Aspirin)

• Dosing, Interactions, etc.

Clinical Context:  Treats mild to moderately severe pain and headache. Inhibits prostaglandin synthesis, which prevents formation of platelet-aggregating thromboxane A2; acts on heat-regulating center of hypothalamus and vasodilates peripheral vessels to reduce fever.

• References

Naproxen (Naprelan, Naprosyn, Aleve, Anaprox)

• Dosing, Interactions, etc.

Clinical Context:  For relief of mild to moderately severe pain; inhibits inflammatory reactions and pain by decreasing activity of cyclooxygenase, which is responsible for prostaglandin synthesis.

• References

Indomethacin (Indocin, Indochron E-R)

• Dosing, Interactions, etc.

Clinical Context:  Rapidly absorbed. Metabolism occurs in liver by demethylation, deacetylation, and glucuronide conjugation. Inhibits prostaglandin synthesis.

• References

Piroxicam (Feldene)

• Dosing, Interactions, etc.

Clinical Context:  Decreases activity of cyclooxygenase, which in turn inhibits prostaglandin synthesis. These effects decrease formation of inflammatory mediators.

• References

Mefenamic acid (Ponstel)

• Dosing, Interactions, etc.

Clinical Context:  Inhibits inflammatory reactions and pain by decreasing prostaglandin synthesis

• References

Class Summary

NSAIDs commonly are used as analgesics in patients with syringomyelia. If one class seems to be ineffective after a 2-week trial, a formulation from another class may be tried. The most commonly used drugs are ibuprofen, acetylsalicylic acid, naproxen, indomethacin, mefenamic acid, and piroxicam.

• References

Methocarbamol (Robaxin)

• Dosing, Interactions, etc.

Clinical Context:  Skeletal muscle relaxant used in conjunction with other therapeutic efforts to treat pain and discomfort associated with musculoskeletal conditions. Acts on CNS to relax certain reflexes.

• References

Class Summary

These agents treat muscle spasms to decrease the patient's level of discomfort.

• References