| Tethered cord | When the spinal cord becomes stuck to the surrounding structures |
| Thoracic | refers to the area from the shoulder blades, through the ribs, to about the beltline. |
| Tonsillar ectopia | a small amount of hang down of the tonsil tissue of the cerebellum. |
| Tonsils | a small, often rounded mass of tissue. There are several tonsils in the body, including in the throat, in the intestine, or in the brain. In reference to Chiari, indicates the tissue tucked behind the cerebellum that protrudes downward, causing a plug effect. |