. | 1. | Pathology. a narrow passage or duct formed by disease or injury, as one leading from an abscess to a free surface, or from one cavity to another. |
| 2. | Surgery. an opening made into a hollow organ, as the bladder or eyeball, for drainage. |
| 3. | Veterinary Pathology. any of various suppurative inflammations, as in the withers of a horse (fistulous withers), characterized by the formation of passages or sinuses through the tissues and to the surface of the skin. |
| 4. | Obsolete. a pipe, as a flute. |

fistula fis·tu·la (fĭs'chə-lə)
n. pl. fis·tu·las or fis·tu·lae (-lē')
An abnormal passage from a hollow organ to the body surface, or from one organ to another.