Pilonidal cysts are fistulas caused by inflammation, they almost always occur above the gluteal cleft. The formation of pilonidal cysts is attributed to ingrown hairs. Excessive sitting is thought to predispose people to the condition because they increase pressure on the coccyx region, pressing hairs further into skin and subcutaneous tissue. This can lead to granuloma, that can become infected and lead to an abscess. A sinus tract may originate from the source of infection and open to the surface of the skin or go deep into the tissue.
The best therapy method has not yet been defined, it is mainly up to the surgeon, depends on his experience and what he deems the best treatment. Pictured here is one of the numerous methods, the marsupialization.