The central canal of the spinal cord is the ependymal-lined cavity running through the centre of the spinal cord, a remnant of the embryonic neural tube lumen. In adults it is largely obliterated by glial tissue but remains patent in some segments. A syrinx (syringomyelia) is a pathological fluid-filled cavity within the spinal cord that may arise from central canal dilation or from intraparenchymal fluid accumulation, typically associated with Chiari malformation, spinal cord tethering, or post-traumatic or post-inflammatory scarring.
Syringomyelia most commonly presents as a cape-like bilateral loss of pain and temperature sensation in the upper limbs (from decussating spinothalamic fibres crossing in the central cord adjacent to the syrinx) with preserved touch and proprioception (dorsal column fibres are lateral to the syrinx). Progressive wasting of the intrinsic hand muscles follows from anterior horn cell involvement. Chiari I malformation (cerebellar tonsils herniating through the foramen magnum) is the most common cause, with CSF flow obstruction driving syrinx formation. Posterior fossa decompression (suboccipital craniectomy) reverses the CSF flow obstruction and allows the syrinx to collapse over months.
Chiari I malformation with tonsillar herniation below the foramen magnum obstructs CSF flow and creates a pressure differential that drives syrinx formation in the cervical and thoracic cord, producing the classic cape distribution sensory loss from crossing spinothalamic fibres; suboccipital decompression and C1 laminectomy with duraplasty restores CSF flow and allows syrinx regression in 70-80% of patients.
