A chronic and often progressive neurological condition in which a cyst (syrinx) fills with cerebrospinal fluid (CSF) inside the spinal cord, often enlarging and further compromising the spinal cord. The extent of damage done by a syrinx often depends on the size in diameter and location of the syrinx (as it tends to affect any areas at or below the syrinx).

These syrinxes are believed to form from the blockage of CSF (such as that which is consistent with a Chiari malformation, a spinal cyst, a bulging/herniated disc, a spinal cord trauma/injury, or even meningitis can cause inflammation that can obstruct the flow of CSF).

Symptoms generally include (from the syrinx down): muscle weakness, pain, and spasms in legs; pain, tingling, burning of arms; muscle wasting (atrophy); loss of reflexes; numbness, pain, and stiffness in back/shoulders/upper chest (cape-like area); neck pain; stiffness of muscles; muscle contractions (fasciculations); bowel & bladder dysfunction; scoliosis; paralysis (rare).