FIGURE 120.21 Large keloid that formed after ear piercing in a susceptible child Lumbosacral Lesions Pilonidal dimples , typically located in the midline of the sacrococcygeal area at the superior aspect of the intergluteal cleft, are benign lesions of no clinical significance On close inspection, there is no evidence of a central pore or opening In contrast, pilonidal sinuses , which are found in the same area, have a small surface opening to a tract lined by stratified squamous epithelium that extends toward, but not into, the spinal canal In some instances, sinuses appear to be of embryonic origin, stemming from either an abnormality of midline fusion or invagination of ectodermal elements The base of such a lesion may consist of a small cyst containing products of skin cells and epithelial appendages, including hair In other cases, the source may be a distorted hair follicle Pilonidal sinuses and cysts are asymptomatic until the sinus becomes obstructed and/or infected This phenomenon is most likely to occur during adolescence or early adulthood Males are more commonly affected than females Excess weight, hirsutism, and a sedentary lifestyle or occupation that requires prolonged sitting also appear to be predisposing factors Infecting organisms usually gain access through the external sinus tract Once infection occurs, an abscess forms and tends to enlarge rapidly Because the overlying skin is thick, expansion tends to occur deep to the skin surface, and