A syrinx is a fluid-filled cavity, or cyst, that develops within the spinal cord, a condition known as Syringomyelia. The syrinx can gradually enlarge, leading to compression and damage of the surrounding nerve fibers that transmit information between the brain and the rest of the body. Symptoms vary widely among individuals, depending heavily on the syrinx’s location, size, and duration.
The Anatomy of a Syrinx and Syringomyelia
The fluid within a syrinx is Cerebrospinal Fluid (CSF), which normally surrounds and protects the brain and spinal cord. The syrinx typically forms as a dilation of the central canal, a small, fluid-filled space running down the middle of the spinal cord. When the normal flow of CSF around the spinal cord or brainstem becomes obstructed, the fluid can be redirected into the spinal cord itself, leading to syrinx formation. As the syrinx expands, it places mechanical pressure on nerve tracts responsible for motor, sensory, and autonomic functions, resulting in progressive neurological deficits. The syrinx most commonly develops in the cervical (neck) or thoracic (upper back) regions of the spine.
Primary Causes of Development
The formation of a syrinx is linked to an underlying condition that disrupts the normal circulation of Cerebrospinal Fluid. The most frequent cause is Type I Chiari Malformation, a structural abnormality accounting for more than half of all cases. In this condition, the cerebellar tonsils herniate through the opening at the base of the skull (foramen magnum) into the spinal canal. This obstruction prevents CSF from flowing normally around the spinal cord, forcing fluid into the cord tissue.
Secondary causes include trauma, tumors, and inflammation. A spinal cord injury can lead to post-traumatic syringomyelia years later due to scarring and CSF blockage. Spinal cord tumors can directly obstruct the fluid pathway. Inflammation of the arachnoid membrane (arachnoiditis) can also create scar tissue that blocks CSF flow and results in syrinx development.
Identifying the Symptoms
Symptoms arise from the damage and compression exerted on the nerve fibers within the spinal cord. The onset is often gradual and progresses slowly over several years. A characteristic early sign is dissociated sensory loss, where the person loses the ability to feel pain and temperature, especially in the hands and upper body, while retaining light touch and vibration. This loss of sensation can present in a ‘cape-like’ distribution over the shoulders, neck, and back.
Motor symptoms involve progressive weakness and muscle atrophy, often beginning in the hands and arms. Patients may also experience stiffness, muscle spasms, and reduced reflexes. If the syrinx extends into lower spinal segments, it can cause difficulty walking, balance problems, and spasticity in the legs. Advanced cases may affect the autonomic nervous system, leading to chronic pain, and bowel or bladder dysfunction.
Diagnosis and Evaluation
Diagnosis begins with a detailed review of the patient’s medical history and a comprehensive neurological examination. The exam assesses motor function, sensory ability, and reflexes to identify patterns of deficit consistent with spinal cord compression. The definitive method for confirming a syrinx is Magnetic Resonance Imaging (MRI). MRI clearly visualizes the syrinx’s location, size, and extent within the spinal cord, and identifies the underlying cause, such as a Chiari Malformation or a spinal cord tumor.
Treatment Approaches
The management of a syrinx depends on the severity of symptoms and whether the condition is stable or progressing. For individuals with a small, non-symptomatic syrinx, observation and regular monitoring are recommended, involving periodic neurological exams and MRI scans. Patients should avoid activities involving straining or heavy lifting, as these can potentially worsen symptoms.
When symptoms are severe or rapidly progressing, surgical intervention is necessary. The primary goal of surgery is to halt the syrinx’s growth and prevent further neurological decline by restoring the normal flow of Cerebrospinal Fluid, not to reverse existing nerve damage.
For syrinxes associated with Chiari Malformation, the most common procedure is a posterior fossa decompression, which involves removing bone from the skull to create space for the cerebellum and relieve pressure. If decompression is ineffective or the syrinx is unrelated to Chiari, a shunting procedure may be performed. Shunting involves inserting a flexible tube to divert fluid from the syrinx to another body cavity, such as the abdomen, where it is absorbed. If the syrinx is caused by a tumor, surgically removing the obstruction can often resolve the syrinx by clearing the fluid pathway.