Posttraumatic syringomyelia (PTS) refers to the development and progression of cerebrospinal fluid (CSF)-filled cavity within the substance of the spinal cord. As the name suggests, this particular type of syringomyelia occurs after known or suspected trauma. It is distinct from syringomyelia occurring due to congenital malformations such as Arnold-Chiari, where obstruction of normal CSF flow through the cerebral ventricles can result in a syrinx occurring as a secondary phenomenon. Other terms which are found in literature or imaging reports which do not precisely define syringomyelia include cystic myelomalacia, hydromyelia, or spinal cord cysts. As the name suggests, a syrinx is tube-like, as in a "syringe."
PTS is difficult to treat, often causes chronic pain, and can result in slow, progressive and potentially devastating loss of sensory and/or motor function, respiratory function, and can result in death.
The pathophysiology of syringomyelia is not definitively known, but several theories exist. Obstruction of normal spinal CSF flow dynamics is felt to be important in the generation of spinal cord syrinxes. This can occur due to scar tissue/adhesions with adherence of the dura mater to the surface of the spinal cord. Spinal canal stenosis may or may not be present. The presence of spinal canal stenosis and bony deformity such as cervical kyphosis is known to increase the likelihood of syrinx formation.
There is no known racial, ethnic or gender-based predisposition for PTS. Around 3% to 4% of persons with spinal cord injury have been reported to develop clinically significant syringomyelia. With the advent and increased use of advanced imaging technology, a higher percentage of persons may be found to have a syrinx. A syrinx can present at any time following spinal cord injury (SCI). The median duration of post-injury diagnosis was 15 years in one study, but onset has been reported as early as 1 month and as late as 45 years after SCI.
The precise pathophysiology is not definitively known, but several theories have been proposed, and this area remains an active point of debate among relevant academic physicians. All relate to abnormalities of CSF flow dynamics. CSF may be forced into the spinal cord due to obstruction of flow by dural adhesion or scarring, and unable to exit because of a one-way valve phenomenon. During coughing and sneezing, changes in CSF pressure which are normally dissipated cannot be due to blockage of normal CSF flow. High versus lower pulse pressure regions may play a role as well. Others have proposed a "Venturi effect" whereby more rapid CSF flow in a region of dural stenosis pulls the spinal cord outward laterally.
Syrinx cavities may take a variety of forms. Some persons may have a single cavity; others may have a second cavity as well. Syrinx cavities may be multiloculated with tissue septations seen on imaging and pathologic specimens. Syrinx cavities are not pure CSF but contain varying amounts of cellular elements and debris. Chronic syrinx cavities may show surrounding gliosis.
Syrinx cavities frequently have tapered ends seen on imaging, and increased spinal cord fluid signal may be seen just beyond the end of the syrinx cavity. Syrinx cavities have traditionally been believed to dissect under pressure through intramedullary tissue.
Pain is the most commonly reported symptom and present variable as localized to the zone of injury or diffusely below the injury level. It is neuropathic and can be aching, burning, stabbing, and may be tender to light touch or pressure. An ascending sensory level may or may not be noticed by the patient.
Pain may increase with sitting up, lying down, coughing, sneezing, or bearing down (Valsalva maneuver). Persons may report a loss in previously present reflex voiding, bowel function or erections.
Tissue tenderness in the zone of injury can feel identical to bruised tissue, yet no bruising is evident. Serial neurologic examinations are critical as these can reveal increased numbness, weakness, changes in tone or spasticity or autonomic changes (hyperhidrosis, heart rate or blood pressure instability). Selective loss of pain and temperature with relative preservation of dorsal column function (touch and pressure) are classic findings. This is also known as "sensory dissociation."
Motor weakness may occur early but is more often a late finding. Some persons may retain motor function despite very large syrinx cavities.
Previously present muscle stretch reflexes may be lost. Autonomic dysreflexia, a sudden increase in blood pressure often associated with a pounding headache, sweating, and other symptoms, may occur or worsen. Worsening orthostatic hypotension may occur.
MRI is the imaging of choice for initial diagnosis of PTS. A serial examination may be done. However, MRI may not be sensitive to changes over time because there is a lack of correlation between symptoms and cavity size. CT myelography may be necessary in persons who cannot undergo MRI, and can also be useful to delineate obstruction to dye flow in CSF due to cord tethering/dural adhesions. Plain radiographs, including flexion-extension views, are used to detect spinal instability, spinal kyphosis, lordosis, fractures, and dislocations. Electromyography may include findings of various forms of abnormal spontaneous activity. However, these are nonspecific, and electrodiagnosis is best used in excluding other causes of symptoms. Motor evoked potentials (MEP) can be used to demonstrate and follow prolongation of central motor conduction time (CMCT). However, MEP technology is not widely available.
Syringomyelia is difficult to treat. Treatment of syrinx cavities is primarily surgical. No surgical treatment has proven uniformly successful, and all treatments are associated with the potential risk of neurologic worsening. Shunting of syrinx cavities (syringoperitoneal, syringopleural, or other) is often attempted initially. Shunts may become clogged with debris and require replacement. Shunt failure with cavity recurrence and shunt-related complications are very high in some series. Other drainage procedures such as needle aspiration, myelotomy are less common. More recently, favored surgical approaches include those aimed at reestablishing normal CSF flow through areas of narrowing due to dural scar, adhesions, and spinal cord tethering. These include laminectomy, intradural exploration, lysis of adhesions, and widening of the CSF space via duraplasty. Although this is a posterior surgical approach, care should be taken to evaluate imaging for anterior tethering as well. In high cervical lesions or cases with extensive multilevel scar tissue, this approach may not be possible. Recurrence of syrinx formation can occur with all procedures (see image).
Serial neurologic examinations are critical for following persons with known syringomyelia. Handheld dynamometry of key muscle grips can provide a useful objective adjunct to manual muscle testing. The person's report of changes in function, such as ambulation, wheelchair propulsion, or transfers, may be the most important, however.
Persons with cervical syringomyelia need monitoring of pulmonary function, including laboratory or bedside PFTs when indicated to assess for worsening of vital capacity.
Interdisciplinary evaluations by rehabilitation teams can assess the need for changes in mobility devices, seating, activities of daily living, to mitigate increasing risks of complications such as pressure ulcers, the decline in mobility, and falls.
Other complications which can occur in persons with syringomyelia include neuropathic arthropathies, also known as Charcot's joint, burns to insensate areas, and increased risks for pressure injuries. Evaluation of scoliosis should be done in persons with known syringomyelia, and vice versa.