It is also called Jeep Bottom, Pilus—hair, Nidus—nest
It is epithelium lined tract, situated short distance behind the anus, containing hairs and unhealthy diseased granulation tissue.
It is due to penetration of hairs through the skin into subcutaneous tissue. It forms granuloma/unhealthy granulation tissue in the deeper plane. It is of infective origin and occurs in sacral region between the buttocks, umbilicus, axilla.
It is common in hair dressers jeep drivers.
Types of hair, force of hair insertion into subcutaneous tissue, vulnerability of the skin are the three factors that cause pilonidal sinus.
Number of hairs collected, acuteness of root end of hairs, type of hair—tough/silky, shape of hair—straight/curled, scaliness of hair are the deciding features of hair. Cut hairs from above descend into cleft and stay there to get buried deep into pilonidal sinus.
Depth, narrowness, friction movements in the natal cleft, soft/macerated skin with erosions, splits, wide skin pores, wounds, presence of moisture and sweat are other factors.
It is common in 20–30 years of age. It is common in males and mostly affects hairy men. Congenital theory is no longer considered; it is an acquired entity. Hair follicles have never been demonstrated in the wall of the sinus.
Number, sharpness, nature, shape of hairs; depth and narrowness of the natal cleft; friction movements; nature of the skin, moisture and sweating are the factors predisposing pilonidal sinus.
Chronic pilonidal sinus can cause occasionally sacral osteomyelitis, necrotising fasciitis and rarely meningitis.