Cyst in Spinal Cord: Causes, Symptoms, and Treatments

A cyst inside the spinal cord, most commonly called a syrinx, is a fluid-filled cavity that forms within the cord tissue itself and can gradually damage the surrounding nerves. The condition is broadly known as syringomyelia, though several other cyst types can also develop in or around the cord. Causes range from structural abnormalities at the base of the skull to spinal injuries, and the cavity can sit silently for years or produce a creeping pattern of pain, numbness, and weakness that worsens over time. Treatment depends heavily on what is driving the cyst’s formation and whether it is growing.

What Actually Forms Inside the Cord

The spinal cord runs inside a column of vertebrae, bathed in cerebrospinal fluid (CSF). When that fluid’s normal flow is disrupted, pressure imbalances can force fluid into the cord’s interior, creating a cavity. In syringomyelia, this cavity, or syrinx, is lined by tissue that keeps it distinct from the normal central canal. It can span a few vertebral segments or stretch across most of the cord’s length. A related but less serious finding is simple dilation of the central canal, which does not always progress. Distinguishing between the two on imaging can be difficult and sometimes requires repeat scans over time.¹

Other cyst types that affect the spinal region include arachnoid cysts (fluid pockets in the membranes surrounding the cord), synovial cysts (arising from degenerated facet joints in the spine), and cystic tumors that hollow out the cord from within. Each has a different origin and behavior, but all can compress or disrupt spinal cord tissue if they grow large enough.

Why Syrinx Cavities Form

The single biggest driver of syringomyelia is anything that blocks or distorts the normal pulsing flow of CSF around the cord. When CSF cannot move freely, abnormal pressure waves push fluid into the cord tissue. Research supports what is sometimes called the pulsatile pressure hypothesis: each heartbeat sends a pressure wave down the spinal canal, and if that wave hits an obstruction, it redirects force into the cord itself, gradually inflating a cavity.² Cine MRI studies have directly visualized this process, showing fluid jetting through the syrinx in sync with the heartbeat, expanding the cavity walls with each pulse.³

The conditions that create this obstruction fall into several categories.

Chiari Malformation

Chiari type I malformation is the most common structural cause. In this condition, the lower part of the brain (the cerebellar tonsils) extends too far down through the opening at the base of the skull, crowding the area where CSF should flow freely between the brain and spinal canal. One case report describes a 42-year-old woman with tonsillar herniation of about 10 mm and a large syrinx stretching from the upper to lower cervical spine.⁴ The relationship between the malformation and the syrinx is well established: relieve the crowding, and the syrinx often shrinks.

Spinal Cord Injury

Trauma to the spine can set the stage for a syrinx months or years after the original injury. In a study of over 500 spinal cord injury patients, about 7% developed syringomyelia within five years, with an average onset around three years after the injury. The severity of the original injury and whether spinal surgery was performed did not predict who would develop a syrinx.⁵ This unpredictability is one reason clinicians monitor spinal cord injury patients with periodic imaging even after they seem stable.

Arachnoid Cysts and Adhesions

A cyst in the membranes around the cord can press on the cord and block CSF circulation, indirectly causing a syrinx to form inside the cord. One documented case involved an arachnoid cyst spanning the lower cervical and upper thoracic spine that compressed the cord and produced a syrinx within the compressed segment. After the arachnoid cyst was surgically removed, the patient’s symptoms resolved.⁶ Similarly, arachnoid adhesions, where the delicate membranes surrounding the cord become scarred and stick together, can silently obstruct CSF flow. These “arachnoid webs” are sometimes invisible on standard imaging and discovered only during surgery.⁷

Other Causes

Spinal cord tumors can generate cysts by blocking fluid flow or by producing fluid themselves. Infections like meningitis or inflammatory conditions can scar the arachnoid membranes and obstruct CSF pathways, sometimes years after the initial illness. In some cases, no clear cause is found at all, and the condition is labeled idiopathic syringomyelia. This “no known cause” category has been shrinking as imaging improves, with occult arachnoid webs now recognized as one previously hidden culprit.

How Symptoms Develop

A syrinx damages the cord from the inside out, and the pattern of symptoms depends on where the cavity sits and how large it grows. Because the syrinx typically starts near the center of the cord, it first disrupts the nerve fibers that cross through the middle, which carry pain and temperature signals. This produces a classic early symptom: you lose the ability to feel hot and cold, or sharp pain, in a band-like pattern across the shoulders, arms, or hands, while your sense of touch and vibration remain intact at first. That dissociation between what you can and cannot feel is sometimes called a “cape-like” sensory loss because it drapes across the upper body.

As the cavity expands, it can produce a wider range of problems:

Pain: headaches at the back of the skull (especially with Chiari-related syrinxes), burning or aching pain radiating down the arms, and deep neck pain. In one surgical series, headache and neck pain were the leading complaints in over 70% of patients.⁸
Weakness: progressive loss of strength, often starting in the hands and arms, which may make gripping objects or performing fine motor tasks increasingly difficult.
Stiffness and spasticity: as the cavity affects motor pathways, the legs can become stiff, spastic, and harder to control.
Bowel and bladder dysfunction: in more advanced cases or when the syrinx extends into the lower cord, bowel and bladder control can deteriorate.

In children, the presentation can be less obvious. A pediatric case series found that spinal arachnoid cysts in children presented as worsening scoliosis, progressive weakness, increasing spasticity, and recurrent urinary infections, symptoms that are easy to attribute to other causes.⁹ A child who develops unexplained scoliosis or a change in gait deserves spinal imaging to rule out an underlying cyst or syrinx.

Symptoms usually develop slowly, over months to years. Rapid worsening can happen but is unusual and should prompt urgent evaluation. The slow pace is both a curse and a blessing: people often adapt to gradual losses without realizing how much function they have surrendered, but the slow progression also means there is often time to intervene before the damage becomes irreversible.

Getting the Diagnosis Right

Standard MRI is the primary tool for detecting spinal cord cysts. A syrinx shows up as a clearly defined fluid-filled space within the cord, typically bright on T2-weighted images. MRI can also reveal the underlying cause in many cases, showing tonsillar herniation in Chiari malformation, cord compression from an arachnoid cyst, or a tumor.

Phase-contrast MRI adds a layer of information that standard scans cannot provide. This technique measures the speed and direction of fluid movement, making it possible to visualize CSF flow around and within the cord. It can detect the abnormal fluid dynamics inside a syrinx, distinguish a true fluid-filled cyst from an area of damaged cord tissue (myelomalacia) that may look similar on standard scans, and evaluate whether CSF flow has been restored after surgery.¹⁰ Patients in worse clinical condition and those with larger cysts tend to show faster fluid velocities inside the syrinx, and those velocities typically drop after successful surgery.¹¹

The distinction between a true syrinx and other spinal cord lesions matters because the treatment differs. A cystic tumor requires a completely different surgical approach than a Chiari-related syrinx, and an area of myelomalacia may not benefit from the same operations at all. When the diagnosis is unclear on a single scan, repeat imaging over several months can clarify the picture: a syrinx tends to be stable or slowly expanding, while a tumor usually grows and enhances with contrast dye.¹

When to Treat and When to Watch

Not every spinal cord cyst needs surgery. Small, stable cysts that cause minimal or no symptoms are often managed with periodic MRI surveillance and clinical monitoring. The natural history of many cyst types remains poorly understood because the medical literature has focused heavily on symptomatic cases, with very little data on how asymptomatic or mildly symptomatic cysts behave over time. That gap in knowledge means the decision to watch rather than operate relies heavily on clinical judgment and the individual patient’s trajectory.

Surgery generally becomes the recommendation when symptoms are progressing, the cyst is enlarging on serial imaging, or the neurological deficits are significant enough to threaten function. The goal of surgery is almost never to drain the cyst directly. Instead, it is to fix whatever is obstructing CSF flow so the cyst can shrink on its own once normal pressure dynamics are restored.

Surgical Approaches

The specific operation depends on the underlying cause.

Posterior Fossa Decompression for Chiari Malformation

When a Chiari malformation is driving the syrinx, the standard approach is posterior fossa decompression: removing a small piece of bone at the back of the skull and often the arch of the first cervical vertebra to create more room for CSF to flow. Many surgeons also enlarge the membrane covering the brain (the dura) with a patch to further open the pathway. Long-term follow-up data support the effectiveness of this operation, with one study documenting sustained benefit in relieving both symptoms and the CSF blockage at the skull-spine junction.¹²

A variation of this procedure preserves the arachnoid membrane (the innermost layer around the brain) rather than opening it. In one series using this arachnoid-preserving technique, 80% of patients had significant symptom improvement, and about two-thirds showed marked shrinkage or collapse of the syrinx on follow-up imaging.¹³ Another series reported pain resolution in 93% of patients, weakness improvement in 71%, and sensory improvement in 69%, with radiological shrinkage of the syrinx in over three-quarters of cases.⁸ These are encouraging numbers, though results vary by patient, and residual symptoms, particularly numbness and subtle weakness, can persist even after the syrinx shrinks.

Arachnoid Lysis for Hidden Adhesions

When the cause is scarring of the arachnoid membrane (whether from previous surgery, infection, or unknown reasons), the surgeon opens the spinal canal, identifies the adhesions under a microscope, and carefully dissects them until CSF flow is restored and the spinal cord is pulsating normally again.⁷ The challenge is that arachnoid adhesions can re-form after surgery, so follow-up imaging is critical.

Shunting

When the underlying cause cannot be addressed directly, or when a syrinx persists despite decompression surgery, a shunt may be placed to drain the fluid. Shunts can route the fluid into the subarachnoid space around the cord, into the abdominal cavity, or into the chest cavity.¹⁴ Shunting is generally considered a second-line option because shunts can clog, migrate, or fail over time, requiring reoperation. They also address the fluid buildup without fixing the root cause, which is why most surgeons prefer to restore natural CSF flow first if possible.

The underlying logic of all these surgical strategies is the same: remove the obstruction, restore normal pressure dynamics, and let the cord’s own fluid-clearance systems drain the syrinx over time. Research suggests that once normal CSF pulsation is reestablished, the cord’s tissue gradually reabsorbs the accumulated fluid, leading to the syrinx shrinkage seen on follow-up imaging.²

A Different Problem Entirely: Facet Joint Synovial Cysts

Synovial cysts are worth mentioning separately because they are sometimes confused with intrinsic spinal cord cysts despite being a completely different entity. These arise from the facet joints of the spine, typically in the lumbar region, when joint degeneration causes the joint capsule to balloon outward and fill with fluid. They press on the nerves in the spinal canal from the outside rather than forming within the cord itself. In a study of patients who underwent surgery for lumbar synovial cysts, those treated with decompression alone had a recurrence rate of about 12%, while those who also had spinal fusion had no recurrences, though both groups had significant symptom improvement.¹⁵ The average time to recurrence was about two years, so if you have had a synovial cyst removed without fusion, continued monitoring is wise.

Living with a Syrinx and the Role of Rehabilitation

Whether you are being monitored conservatively or recovering from surgery, rehabilitation plays a real role. Physiotherapy focused on maintaining strength, flexibility, and functional independence has shown measurable benefits: in one review, about 75% of patients with primary syringomyelia reported symptom improvement and better quality of life with structured physiotherapy.¹⁶ This does not mean exercise shrinks the cyst. Rather, it helps preserve the function of the nerves and muscles that remain healthy, prevents deconditioning, and manages chronic pain.

Some patients manage surprisingly well without surgery. The 42-year-old woman with Chiari malformation and a large cervical syrinx mentioned earlier was treated with three months of physiotherapy after surgery was deemed inappropriate. Over two years of follow-up, her symptoms gradually resolved and the syrinx actually shrank on imaging.⁴ Cases like this are not the norm, but they reinforce the idea that the decision to operate should weigh the trajectory carefully rather than react to the imaging alone. A stable or improving patient with a large-looking cyst on MRI may not need surgery, while a patient with a small syrinx and worsening symptoms likely does.

Stem Cell Research and Future Directions

One area of active investigation is whether transplanting neural stem cells into the damaged cord can prevent a syrinx from expanding. In a rat model of post-traumatic syringomyelia, transplanted human neural stem and progenitor cells significantly limited cyst growth compared to animals that received sham transplants.¹⁷ The transplanted cells appear to fill the damaged area, providing structural support and potentially reducing the inflow of fluid. This is far from clinical application; no human trials have been completed for syringomyelia specifically. But for the subset of patients whose post-traumatic syrinx cannot be addressed by restoring CSF flow alone, biological therapies like this represent a genuinely different approach to the problem. The gap between a promising animal study and a safe, effective human treatment is typically measured in decades, but the principle is encouraging: rather than only rerouting fluid, you might one day be able to rebuild the tissue barrier that keeps it out.

1
World Neurosurgery. How Should Syringomyelia be Defined and Diagnosed?
2
PubMed Central. Pulsatile intraspinal pressure drives post-traumatic syringomyelia: evidence supporting the CSF pulsatile pressure dynamic equilibrium hypothesis
3
American Journal of Neuroradiology. Syringomyelia Fluid Dynamics and Cord Motion Revealed by Serendipitous Null Point Artifacts during Cine MRI
4
Cureus. The Pathogenesis of Chiari Malformation and Syringomyelia: A Case Report and Systematic Review of Current Theories
5
Nature / Spinal Cord. Factors associated with early onset post-traumatic syringomyelia
6
Europe PMC. Syringomyelia associated with a spinal arachnoid cyst
7
PubMed Central. A Novel Clinical Insight Into Idiopathic Syringomyelia With Occult Arachnoid Webs: Neuropathological Features, Differential Diagnosis, and Surgical Strategy
8
Nepal Journal of Neuroscience. Outcome of Posterior Fossa Decompression for Chiari Type I Malformation with Syringomyelia
9
PubMed. Spinal arachnoid cysts in the pediatric age group: an association with neural tube defects
10
Polish Journal of Radiology. Imaging of cerebrospinal fluid flow: fundamentals, techniques, and clinical applications of phase-contrast magnetic resonance imaging – Section: Syringomyelia
11
PubMed Central. Cerebrospinal fluid flow imaging by using phase-contrast MR technique
12
PubMed. Long-term results after posterior fossa decompression in syringomyelia with adult Chiari Type I malformation
13
PubMed. Surgical results of arachnoid-preserving posterior fossa decompression for Chiari I malformation with associated syringomyelia
14
Journal of Neurosurgery: Spine. Syrinx shunts for syringomyelia: a systematic review and meta-analysis of syringosubarachnoid, syringoperitoneal, and syringopleural shunting
15
PubMed. The Variability of Lumbar Facet Joint Synovial Cyst Recurrence Requiring Revision Surgery After Decompression-only and Decompression/Fusion
16
PubMed Central. Active Conservative Management of Primary Syringomyelia: A Scoping Review and Perspectives for an Activity-Based Clinical Approach
17
Neurotherapeutics. Neural Stem/Progenitor Cell Transplantation Prevents Cyst Expansion in a Rat Model of Posttraumatic Syringomyelia