fistula. A pathologic sinus leading from an abscess cavity to the surface.

Fistula  (pl. fistulae) is an abnormal communication between the surface and an internal part of the body, or between two natural cavities or canals. The first form is seen in a rectal fistula, the second in vesicovaginal fistula. Fistulae may result from a congenital defect and can arise from sloughing, traumatism and suppuration. Fistulae are named from their situation and communication.