A pilonidal sinus is a blind-end tract lined with granulation tissue, which leads to a cystic cavity lined with epithelial tissue. As the name suggests, these hair containing abscesses are usually found in the sacrococcygeal region. However, they may also occasionally occur in the axilla, groin, interdigital web, umbilicus, nose, inter mammary areas, suprapubic area, clitoris, prepuce, penis, occiput or on the feet. The sinus is caused by the friction of the skin at the base of the spine, leading to the embedding of the hair beneath the surface. The hair forms small cavities or pits, which are in truth, enlarged hair follicles, which go on to become sinuses. Bacteria and debris enter this sterile area, producing local inflammation and formation of pus-filled abscesses. In chronic condition, the sinus becomes an open cavity, constantly draining small amounts of fluid. Occasionally malignant tumors, mostly primary, may arise in a PNS.
The frequency of PNS has been calculated to be 26 cases per 100,000 people in the US. The disease shows a male predominance, with males showing 2.2-4 times greater tendency to exhibit the disease. Affected patients are usually between the ages of 25-40 years. Treatment for symptomatic PNS involves surgery to incise and drain the abscess. The surgery can be either wide excision and healing by secondary intention (longer healing time, low chance of recurrence), excision and primary closure by sutures (quicker healing, risk of recurrence), or plastic surgery technique (for recurring and/or extensive sinus).
There has been controversy and disagreement regarding the acquired or congenital nature of the pilonidal disease. However, it is generally agreed that although the disorder per se is acquired, the formation of the pits through which the hair enters the subcutaneous tissue is congenital. A recent report has shown a significant association between mutations in the protein kinase, cAMP-dependent, regulatory, type I, alpha (PRKAR1A) gene and pilonidal disease, suggesting a hereditary predisposing abnormality.