a short tract leading from an opening in the skin in or near the cleft at the top of the buttocks and containing hairs. The sinus may be recurrently infected, leading to pain and the discharge of pus. Treatment is by surgical opening and cleaning of the sinus.
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a suppurating fistulous tract, most often in the coccygeal region (coccygeal sinus) and containing a tuft of hair; occasionally these are found in other regions of the body. It is usually the result of repeated friction that has caused hairs to penetrate the skin. Called also piliferous cyst, pilonidal cyst, and pilonidal fistula.Medical dictionary. 2011.