Clinical meaning
Syringomyelia is a chronic progressive disorder characterized by the formation of a fluid-filled cavity (syrinx) within the spinal cord, most commonly in the cervical region. The syrinx expands over time, damaging neural tissue from the center of the cord outward. The most common cause is Chiari malformation type I (CM-I), where cerebellar tonsils herniate through the foramen magnum, obstructing normal CSF flow at the craniocervical junction. This obstruction creates abnormal CSF pressure dynamics that force fluid into the central canal of the spinal cord, forming and expanding the syrinx. Other causes include post-traumatic (spinal cord injury → arachnoiditis → syrinx formation months to years later), spinal cord tumors (intramedullary tumors obstruct CSF flow), and tethered cord. The classic clinical presentation reflects the syrinx's central location, initially damaging the anterior white commissure where pain and temperature fibers cross (spinothalamic tract decussation): 'cape-like' or 'suspended' dissociated sensory loss — loss of pain and temperature sensation in a shawl-like distribution across the shoulders, arms, and upper back, while light touch and proprioception (carried in the posterior columns) are PRESERVED. This dissociated sensory loss is pathognomonic. As the syrinx expands, it damages anterior horn cells (lower motor neuron signs: weakness, atrophy, fasciculations in the hands and arms), lateral corticospinal tracts (upper motor neuron signs: spasticity, hyperreflexia in the legs), and autonomic pathways (Horner syndrome: ptosis, miosis, anhidrosis).