| Shunt | small, soft plastic tube that is used to drain fluid. |
| Sleep apnea | to stop breathing intermittently when sleeping. Symptom can be described as waking up short of breath or gasping for air. |
| Syncope | Spells of passing out, or fainting (loss of consciousness). Different from a seizure. |
| Syringomyelia | the condition of having an abnormal fluid cavity in the spinal cord |
| Syrinx | abnormal fluid cavity in the spinal cord |