Caption

A pilonidal sinus, a chronic abscess that develops in a congenital opening in the skin near the cleft at the top of the buttocks. Hair shafts, from local follicles or shed body hair, are present in the abscess & act as a focus for persistent inflammation. Healing is hindered by the presence of such non-degradable material. As part of the attempt at healing, epithelium migrates from the skin surface to form a sinus (a track) through the abscess cavity. Treatment of the abscess requires surgery to open and clean the sinus.