A syrinx is a rare neurological disorder characterized by the development of a tubular, fluid-filled cavity within the central nervous system. When this pathological cavity forms in the spinal cord, the condition is known as syringomyelia; when it affects the brainstem, it is called syringobulbia. The development of a syrinx can compress and injure the nerve fibers that transmit information between the brain and the body, causing various neurological deficits.
The Fluid-Filled Cavity: Location and Formation
A syrinx is a fluid-filled cavity that develops within the tissue of the spinal cord. The fluid inside the syrinx is cerebrospinal fluid (CSF), which normally surrounds and cushions the brain and spinal cord. Syringomyelia typically occurs in the cervical and thoracic regions, though the cavity can extend along the entire length. This cyst expands over time, leading to the compression and destruction of the surrounding spinal cord tissue.
The formation of a syrinx begins with a disruption in the normal circulation of CSF. A blockage redirects the fluid, causing excess CSF to accumulate within the spinal cord’s central canal. The resulting pressure expands this central canal, leading to the formation of the tube-like syrinx. The continual movement of this fluid within the cyst, driven by pressure differences, causes the syrinx to grow and further damage the spinal cord.
Underlying Causes of Syrinx Development
The primary mechanism leading to syrinx formation is any condition that obstructs the normal flow and pressure dynamics of cerebrospinal fluid. The most frequent underlying cause is Chiari Malformation Type I, which accounts for the majority of cases. This congenital condition involves the cerebellar tonsils extending down through the foramen magnum (the opening at the base of the skull) and into the spinal canal. This displacement impairs the movement of CSF between the skull and the spine, leading to fluid pressure buildup.
Other conditions and traumas can also initiate syrinx development by causing blockages or scarring. Scarring from previous spinal cord trauma is a significant factor in acquired syrinx cases, often leading to post-traumatic syringomyelia. Spinal cord tumors can directly obstruct the CSF pathway, and the syrinx may resolve if the tumor is surgically removed. Inflammatory conditions, such as arachnoiditis (inflammation of the membrane surrounding the spinal cord), can also cause scarring that impedes fluid flow and contributes to cyst formation.
Symptoms and Neurological Presentation
The symptoms associated with a syrinx depend on its size, location, and the extent of damage to the spinal cord’s nerve tracts. A characteristic neurological deficit is the loss of pain and temperature sensation, often starting in the hands and extending across the shoulders and upper back in a “cape-like” distribution. This sensory loss occurs because the syrinx typically begins in the center of the spinal cord, where the nerve fibers carrying these signals cross. Conversely, sensations like light touch, position, and vibration are often preserved initially because those nerve tracts are located more peripherally in the cord.
As the syrinx expands, it affects motor neurons, leading to progressive muscle weakness, atrophy, and stiffness, particularly in the hands and arms. Patients may experience muscle twitching and a loss of reflexes. Chronic pain in the neck, back, or extremities is also a common symptom. The long-term progression can lead to spastic leg weakness, balance issues, and, in advanced cases, bladder and bowel dysfunction.
If the syrinx extends upward into the brainstem (syringobulbia), the presentation involves cranial nerve functions. Symptoms in these rare cases include dizziness, involuntary rapid eye movements (nystagmus), and difficulty with speech or swallowing. The neurological deficits often progress slowly, sometimes beginning in adolescence or early adulthood. The first sign may be a painless injury, such as a burn, that goes unnoticed due to the loss of sensation.
Diagnosis and Management Approaches
The definitive method for identifying and characterizing a syrinx is Magnetic Resonance Imaging (MRI) of the entire spinal cord and brain. MRI provides detailed images that show the syrinx’s location, size, and extent, and it can also detect the underlying cause, such as a Chiari malformation or a spinal cord tumor. A specialized technique called cine-MRI may be used to visualize the flow dynamics of the cerebrospinal fluid, which helps in understanding the mechanism of syrinx formation.
The goal of treatment is to halt the syrinx’s progression and alleviate neurological symptoms by restoring the normal circulation of CSF. For asymptomatic patients, careful monitoring with periodic neurological exams and MRI scans is the initial approach. If symptoms are present or worsening, surgical intervention is recommended to address the underlying cause. In cases linked to Chiari Malformation Type I, a neurosurgeon may perform a craniocervical decompression to create more space at the base of the skull and relieve the CSF obstruction. If the syrinx has no identifiable cause or continues to grow, a shunt or stent may be surgically implanted to drain the excess fluid into another body cavity, such as the chest or abdomen.