An infected tract leading from a focus of infection to the skin or a hollow organ. It is sometimes also called a fistula. The tract is lined with epithelium. Although usually draining into the mouth, sinus tracts may lead from a focus of infection such as an infected tooth or periodontal disease to drain on the face or neck (cutaneous sinus tract). When a cutaneous sinus tract is present, the infected tooth is often asymptomatic, as the tract provides a pathway for inflammatory exudates, thereby relieving the pressure. Cutaneous dental sinus tracts may resemble a pimple, ulcer, or nodule.