While often confused due to their similar appearance on imaging, syringomyelia (syrinx) and hydromyelia are distinct conditions affecting the spinal cord, differing primarily in their origin, nature, and progression. The fundamental distinction lies in syringomyelia being an acquired, often progressive fluid-filled cavity associated with abnormal cerebrospinal fluid (CSF) circulation, whereas hydromyelia is a non-evolving, persistent central canal, typically present from birth.
Understanding Syringomyelia (Syrinx)
Syringomyelia, commonly referred to as a "syrinx," is a chronic and progressive neurological disorder characterized by the formation of a fluid-filled cyst, or syrinx, within the spinal cord. This cavity can expand over time, leading to damage to the spinal cord and a variety of neurological symptoms.
Key Characteristics of Syringomyelia:
- Pathogenesis: It is often associated with an intrinsic pathogeny of abnormal CSF circulation in the subarachnoid space (SAS). This disruption leads to fluid accumulating within the spinal cord tissue, forming the syrinx.
- Nature: The cavity is typically evolutive, meaning it can enlarge and extend over time, putting pressure on nerves and causing symptoms.
- Causes: Syringomyelia is primarily an acquired condition. Common underlying causes include:
- Chiari Malformations: Especially Chiari I malformation, where cerebellar tonsils extend into the spinal canal.
- Spinal Cord Trauma: Injuries can disrupt CSF flow.
- Spinal Cord Tumors: Both benign and malignant tumors can obstruct CSF pathways.
- Arachnoiditis: Inflammation of the arachnoid membrane, leading to scar tissue and CSF flow blockages.
- Symptoms: As the syrinx expands, it can cause:
- Chronic pain, often described as burning or shooting, in the neck, shoulders, arms, or back.
- Weakness and muscle atrophy in the hands and arms.
- Loss of sensation, particularly to temperature and pain, leading to frequent burns or injuries that go unnoticed.
- Stiffness in the back, neck, shoulders, and extremities.
- Bowel and bladder dysfunction in advanced cases.
For more information, you can visit the National Institute of Neurological Disorders and Stroke (NINDS) page on Syringomyelia.
Understanding Hydromyelia
Hydromyelia refers to a persistent or mildly enlarged central canal of the spinal cord. Unlike a syrinx, it is generally considered a developmental variation rather than a disease process, and it rarely causes significant neurological issues.
Key Characteristics of Hydromyelia:
- Pathogenesis: Hydromyelia is a non-evolutive thin cavity located at the central canal. It can be assimilated to a persistent central canal, which is a normal anatomical structure present during fetal development that typically closes or becomes very narrow in adulthood.
- Nature: It is almost always non-progressive and non-evolutive, meaning the dilation does not typically expand or cause damage over time.
- Causes: Hydromyelia is usually congenital, often identified incidentally during imaging for other reasons. It is generally not associated with the same intrinsic pathogeny of abnormal CSF circulation in the subarachnoid space as syringomyelia.
- Symptoms: Most individuals with hydromyelia are asymptomatic. When symptoms do occur, they are typically mild and non-specific, often related to the underlying condition if hydromyelia is secondary to another issue.
Key Differences Between Syringomyelia and Hydromyelia
There is often confusion in the denomination between syringomyelia and hydromyelia. The following table highlights their primary distinctions:
| Feature | Syringomyelia (Syrinx) | Hydromyelia |
|---|---|---|
| Nature of Cavity | Fluid-filled cyst/cavity within the spinal cord tissue. | Dilation of the central canal of the spinal cord. |
| Origin/Cause | Associated with abnormal CSF circulation in SAS; often acquired due to conditions like Chiari malformation, trauma, or tumors. | Can be assimilated to a persistent central canal; typically congenital or a developmental variation. |
| Progression | Often evolutive and progressive; the cavity can expand and cause increasing symptoms. | Non-evolutive and typically non-progressive; the dilation usually remains stable. |
| Clinical Impact | Frequently symptomatic, causing significant neurological deficits. | Usually asymptomatic and an incidental finding. |
| Underlying Pathogeny | Intrinsic pathogeny of abnormal CSF circulation in the subarachnoid space. | Generally, no intrinsic pathogeny of abnormal CSF circulation in the SAS; a persistent normal anatomical structure. |
| Treatment | May require surgical intervention to prevent progression and alleviate symptoms. | Typically requires no treatment; observation is usually sufficient. |
Clinical Significance and Diagnosis
Distinguishing between syringomyelia and hydromyelia is crucial for prognosis and treatment planning. Both conditions are primarily diagnosed using Magnetic Resonance Imaging (MRI) of the spinal cord, which can clearly visualize the fluid-filled cavities. Radiologists and neurologists use specific criteria, including the size, location, and presence of associated abnormalities, to differentiate between the two. A syrinx often appears more irregular and larger, extending beyond the confines of the central canal, while hydromyelia typically presents as a thin, uniform dilation limited to the central canal.
