Quick answer: A posttraumatic spinal cord syrinx is a fluid-filled cavity that can form inside the spinal cord months or years after a spinal cord injury. Scar tissue, which forms between the spinal cord and the canal around it, places the spinal cord on abnormal stretch and impairs the flow of spinal fluid around it. Together, these can allow spinal fluid to enter into the spinal cord tissue at first causing a softening of the spinal cord tissue, known as myelomalacia, which can further progress to fluid-filled pockets or cystic cavitation, also referred to as a syrinx.
Key takeaways
- A syrinx is a fluid-filled cavity that forms inside the spinal cord.
- It can develop months or years after a spinal cord injury.
- The spinal cord normally has mobility within the spinal canal and moves with cerebrospinal fluid flow and with flexion and extension of the spine.
- After trauma, scar tissue and tethering may reduce that normal mobility and change fluid dynamics.
- Not every person with posttraumatic tethering develops a syrinx, and not every syrinx causes symptoms.
- Progression over time matters. A syrinx can remain stable, or it can enlarge and begin to affect function.
What is a posttraumatic spinal cord syrinx?
After a spinal cord injury, most people focus on healing, rehabilitation and adapting to life after trauma. What can be harder to anticipate is that some spinal cord changes may continue to evolve over time.
One of those delayed changes is a posttraumatic syrinx, also called posttraumatic syringomyelia. A syrinx is a fluid-filled cavity that forms within the spinal cord itself. It is not a pocket of fluid outside the cord. It is a change inside the cord tissue.
A syrinx may appear months or even years after the original spinal cord injury.
How can a syrinx form after spinal cord injury?
To understand how a syrinx may form, it helps to understand how the spinal cord normally functions inside the spine.
The spinal cord is surrounded by cerebrospinal fluid, or CSF, the clear fluid that cushions the brain and spinal cord. It is also surrounded by the dura, the tough outer covering that contains the spinal cord and CSF.
Under normal conditions, the spinal cord has mobility within the spinal canal. It moves with CSF flow and also with normal flexion and extension of the spine. That normal motion matters.
After trauma, scar tissue can develop around the spinal cord and nearby structures. That scarring can restrict the cord’s normal mobility and alter how CSF moves around it. Over time, those abnormal forces may contribute to the formation of a syrinx within the cord.
Scott Falci, MD of the HCA HealthONE Falci Institute for Spinal Cord Injuries explains, “The spinal cord normally moves with cerebrospinal fluid flow and with flexion and extension of the spine. When trauma and scarring interfere with that normal motion, the cord can be exposed to abnormal mechanical and fluid forces over time, and that may lead to the development of a syrinx.”
Why does it often develop later, not right away?
A symptomatic posttraumatic syrinx is often not an immediate complication. It tends to develop gradually but can present anywhere from months to decades after the spinal cord injury.
That is because the underlying process also tends to unfold gradually:
- Scar tissue matures over time
- The cord’s normal mobility is changed
- CSF flow is disrupted
- Repeated abnormal stress on the cord may slowly lead to cavity formation or enlargement
This delayed timeline is one reason long-term follow-up after spinal cord injury can be so important.
How is tethering related to syrinx formation?
In all posttraumatic cases, syrinx formation and tethering are closely related.
A posttraumatic tethered spinal cord means the cord is abnormally attached to surrounding tissues, limiting its normal mobility within the spinal canal. If the cord cannot move normally with CSF flow and with bending or straightening of the spine, abnormal stretch of the neural elements will occur. Additionally, tethering impairs CSF flow around the spinal cord, creating a pressure change, which can be harmful.
That does not mean every person with tethering develops a syrinx. It also does not mean every syrinx causes symptoms. But tethering is a part of the overall process.
“In all patients with a traumatic spinal cord injury, we see development of spinal cord tethering at the injury site. Some will additionally develop progressive syrinx formation,” Dr. Falci says. “But recommendations for surgical intervention will depend on the significance of the patient’s symptoms.”
Does a syrinx always get worse?
No. Many syrinxes remain stable and do not cause major symptoms over long periods of time. Others, however, may enlarge and progressively interfere with spinal cord function over time.
What raises concern is progression of symptoms over time, especially when imaging changes are paired with new symptoms, worsening pain, or declining neurologic function.
When should a syrinx be suspected?
A syrinx may be considered when a person with a past spinal cord injury develops:
- Progressive weakness
- Sensory changes
- New pain
- Increasing spasticity
- Changes in bowel or bladder function
- New autonomic symptoms such as changes in sweating patterns or abnormal blood pressure swings
Still, these symptoms are not specific to syrinx alone.
Other causes should also be ruled out
People with spinal cord injury can develop new symptoms for many reasons. Before concluding that a syrinx is responsible, clinicians may also consider:
- Skeletal issues such as ruptured disc, spinal stenosis, spinal instability
- Peripheral nerve compression
- Primary neurodegenerative processes (e.g., Multiple Sclerosis, ALS, etc.)
- Other causes of neuropathic pain, autonomic dysreflexia, spasticity, abnormal sweating
- Urinary tract infections
- Skin sores
- Kidney stones, bladder stones
- Abnormal bone formation (heterotopic ossification)
That broader evaluation is important because symptoms can overlap.
FAQ
What is the difference between a syrinx and a cyst?
A syrinx is often described as a cyst, but more specifically, it is a fluid-filled cavity within the spinal cord.
Can a syrinx form years after SCI?
Yes. It may develop months or years after the original injury.
Is tethering always involved?
Tethering is part of the process, but the relationship is not always simple or identical in every patient.
Does every syrinx need treatment?
No. Treatment depends on symptoms, progression and the full clinical picture.