Syringomyelia is a condition in which a fluid-filled cavity, called a syrinx, forms inside the spinal cord. This cavity can expand over time, damaging nerve fibers and producing progressive neurological symptoms like pain, weakness, and sensory loss. The condition is most commonly linked to a structural brain abnormality called Chiari malformation, but it can also develop after spinal cord injuries, tumors, or inflammation.
How a Syrinx Forms
Your spinal cord is surrounded by cerebrospinal fluid (CSF), which normally flows freely around the brain and spine. Syringomyelia develops when something disrupts that flow. The blockage creates abnormal pressure differences that force fluid into the spinal cord tissue itself, where it pools and forms a cavity.
The most widely accepted explanation involves a “water-hammer” effect: with each heartbeat, blocked CSF pulses against the spinal cord, gradually driving fluid inward. Everyday actions that increase spinal pressure, like coughing or sneezing, can worsen this process by pushing fluid through tiny channels along the spinal cord’s surface. Current research suggests the fluid that fills a syrinx isn’t pure CSF but rather a filtered version of blood plasma, created by the pressure imbalance between the fluid surrounding the cord and the fluid inside it.
Common Causes
The most frequent cause is Chiari type 1 malformation, a condition where the lower part of the brain (the cerebellar tonsils) extends downward through the opening at the base of the skull. This herniation blocks CSF flow at the junction between the brain and spinal cord. The majority of people diagnosed with syringomyelia that has no other obvious explanation turn out to have a Chiari malformation on imaging.
The Chiari malformation itself appears to result from the skull’s posterior fossa (the space at the back of the skull that houses the cerebellum) being too small. Whether this stems from problems during fetal development or insufficient bone growth remains debated, but the end result is the same: overcrowding pushes brain tissue downward, obstructing CSF pathways.
Syringomyelia can also develop after spinal cord trauma, spinal tumors, infections like meningitis, or tethered spinal cord. In post-traumatic cases, scar tissue or spinal deformity creates the CSF blockage that sets the process in motion.
What Symptoms Feel Like
The hallmark of syringomyelia is a distinctive pattern of sensory loss. Because the syrinx typically forms in the center of the spinal cord, it first damages the nerve fibers that cross there, which are the ones carrying pain and temperature signals. This produces a characteristic “cape-like” distribution of lost sensation across the neck, shoulders, arms, and hands. You might burn or cut yourself without feeling it. Meanwhile, your sense of touch, vibration, and body position often remains intact early on, because those signals travel along different pathways at the cord’s edges.
As the syrinx expands, additional symptoms develop. Muscle weakness and wasting in the hands and arms are common. Chronic pain, often described as burning or aching in the neck and shoulders, affects many people. Stiffness and spasticity in the legs can appear if the cavity extends further down the cord. Some people also develop scoliosis, particularly children and adolescents, which is sometimes the first sign that leads to diagnosis.
Symptoms typically develop slowly over months to years, though post-traumatic syringomyelia can progress more quickly. The gradual onset means many people live with mild symptoms for a long time before seeking evaluation.
How It Is Diagnosed
MRI is the standard tool for diagnosing syringomyelia. On MRI, a syrinx appears as a well-defined fluid-filled cavity within the spinal cord, often spanning multiple vertebral segments. The scan also reveals the underlying cause in most cases, whether that’s a Chiari malformation, a tumor, or post-traumatic scarring. Specialized CSF flow studies using MRI can show exactly where and how fluid movement is blocked, which helps guide treatment decisions.
Surgical Treatment and What to Expect
Not every syrinx requires surgery. Small, stable cavities in people without symptoms can sometimes be monitored with periodic MRI scans. Once symptoms appear, however, surgical intervention is generally recommended to prevent further spinal cord damage.
The most common and effective surgery for Chiari-associated syringomyelia is posterior fossa decompression with duraplasty. The surgeon removes a small portion of bone at the base of the skull and opens the tough membrane (dura) surrounding the brain, then patches it with additional tissue to create more space. This restores CSF flow across the blocked area. Studies consistently show this approach resolves or significantly shrinks the syrinx in 75% to 90% of cases, with about 75% of patients experiencing meaningful symptom improvement.
When decompression alone doesn’t resolve the syrinx, a shunt procedure may follow. This involves placing a small tube directly into the syrinx to drain fluid into the surrounding spinal fluid space or the chest cavity. Shunting is generally reserved as a second-line option because it carries higher long-term risks of the tube malfunctioning or the syrinx recurring. Newer techniques, including ventral shunt placement, have improved durability and reduced malfunction rates.
Recovery Timeline
After decompression surgery, the syrinx doesn’t disappear overnight. In a prospective study tracking patients with serial MRIs, the cavity showed little change at one week. By three to six months, all syrinxes had decreased in both diameter and length. The median time for the syrinx to shrink by more than 50% was 3.6 months. On average, cavities shrank from about 7 mm across before surgery to less than 1.5 mm at last follow-up.
An encouraging finding is that clinical improvement often happens before the syrinx visibly shrinks on imaging. Relief of spinal cord pressure starts producing benefits even while the cavity is still present on MRI. However, the recovery picture is nuanced: while 94% of patients in one longitudinal study had improved symptoms after surgery, 68% had incomplete resolution. About half continued to experience abnormal sensations, and nearly 60% had some residual sensory loss. This doesn’t mean the surgery failed. It reflects the fact that a syrinx can permanently injure nerve fibers before it’s treated, and that damage doesn’t fully reverse.
In children with scoliosis caused by syringomyelia, early decompression stabilized or improved spinal curvature in roughly two-thirds of cases.
What Happens Without Treatment
Left untreated, a syrinx can continue to expand and cause progressive, irreversible spinal cord injury. The most serious complication is myelopathy, where sustained compression and damage to the cord leads to significant disability. Over time, this can progress to paralysis of the legs (paraplegia) or all four limbs (quadriplegia), loss of bladder and bowel control, and recurrent pneumonia from weakened respiratory muscles. The damage accumulates gradually, which is why early detection and treatment matter even when symptoms seem mild.